lib/littlefs: Add littlefs v2.1.3 source.

4 files changed, 5656 insertions, 0 deletions

diff --git a/lib/littlefs/lfs2.c b/lib/littlefs/lfs2.c
new file mode 100644
index 0000000000..dea01b1c07
--- /dev/null
+++ b/lib/littlefs/lfs2.c
@@ -0,0 +1,4742 @@
+/*
+ * The little filesystem
+ *
+ * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#include "lfs2.h"
+#include "lfs2_util.h"
+
+#define LFS2_BLOCK_NULL ((lfs2_block_t)-1)
+#define LFS2_BLOCK_INLINE ((lfs2_block_t)-2)
+
+/// Caching block device operations ///
+static inline void lfs2_cache_drop(lfs2_t *lfs2, lfs2_cache_t *rcache) {
+    // do not zero, cheaper if cache is readonly or only going to be
+    // written with identical data (during relocates)
+    (void)lfs2;
+    rcache->block = LFS2_BLOCK_NULL;
+}
+
+static inline void lfs2_cache_zero(lfs2_t *lfs2, lfs2_cache_t *pcache) {
+    // zero to avoid information leak
+    memset(pcache->buffer, 0xff, lfs2->cfg->cache_size);
+    pcache->block = LFS2_BLOCK_NULL;
+}
+
+static int lfs2_bd_read(lfs2_t *lfs2,
+        const lfs2_cache_t *pcache, lfs2_cache_t *rcache, lfs2_size_t hint,
+        lfs2_block_t block, lfs2_off_t off,
+        void *buffer, lfs2_size_t size) {
+    uint8_t *data = buffer;
+    LFS2_ASSERT(block != LFS2_BLOCK_NULL);
+    if (off+size > lfs2->cfg->block_size) {
+        return LFS2_ERR_CORRUPT;
+    }
+
+    while (size > 0) {
+        lfs2_size_t diff = size;
+
+        if (pcache && block == pcache->block &&
+                off < pcache->off + pcache->size) {
+            if (off >= pcache->off) {
+                // is already in pcache?
+                diff = lfs2_min(diff, pcache->size - (off-pcache->off));
+                memcpy(data, &pcache->buffer[off-pcache->off], diff);
+
+                data += diff;
+                off += diff;
+                size -= diff;
+                continue;
+            }
+
+            // pcache takes priority
+            diff = lfs2_min(diff, pcache->off-off);
+        }
+
+        if (block == rcache->block &&
+                off < rcache->off + rcache->size) {
+            if (off >= rcache->off) {
+                // is already in rcache?
+                diff = lfs2_min(diff, rcache->size - (off-rcache->off));
+                memcpy(data, &rcache->buffer[off-rcache->off], diff);
+
+                data += diff;
+                off += diff;
+                size -= diff;
+                continue;
+            }
+
+            // rcache takes priority
+            diff = lfs2_min(diff, rcache->off-off);
+        }
+
+        // load to cache, first condition can no longer fail
+        LFS2_ASSERT(block < lfs2->cfg->block_count);
+        rcache->block = block;
+        rcache->off = lfs2_aligndown(off, lfs2->cfg->read_size);
+        rcache->size = lfs2_min(
+                lfs2_min(
+                    lfs2_alignup(off+hint, lfs2->cfg->read_size),
+                    lfs2->cfg->block_size)
+                - rcache->off,
+                lfs2->cfg->cache_size);
+        int err = lfs2->cfg->read(lfs2->cfg, rcache->block,
+                rcache->off, rcache->buffer, rcache->size);
+        LFS2_ASSERT(err <= 0);
+        if (err) {
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+enum {
+    LFS2_CMP_EQ = 0,
+    LFS2_CMP_LT = 1,
+    LFS2_CMP_GT = 2,
+};
+
+static int lfs2_bd_cmp(lfs2_t *lfs2,
+        const lfs2_cache_t *pcache, lfs2_cache_t *rcache, lfs2_size_t hint,
+        lfs2_block_t block, lfs2_off_t off,
+        const void *buffer, lfs2_size_t size) {
+    const uint8_t *data = buffer;
+
+    for (lfs2_off_t i = 0; i < size; i++) {
+        uint8_t dat;
+        int err = lfs2_bd_read(lfs2,
+                pcache, rcache, hint-i,
+                block, off+i, &dat, 1);
+        if (err) {
+            return err;
+        }
+
+        if (dat != data[i]) {
+            return (dat < data[i]) ? LFS2_CMP_LT : LFS2_CMP_GT;
+        }
+    }
+
+    return LFS2_CMP_EQ;
+}
+
+static int lfs2_bd_flush(lfs2_t *lfs2,
+        lfs2_cache_t *pcache, lfs2_cache_t *rcache, bool validate) {
+    if (pcache->block != LFS2_BLOCK_NULL && pcache->block != LFS2_BLOCK_INLINE) {
+        LFS2_ASSERT(pcache->block < lfs2->cfg->block_count);
+        lfs2_size_t diff = lfs2_alignup(pcache->size, lfs2->cfg->prog_size);
+        int err = lfs2->cfg->prog(lfs2->cfg, pcache->block,
+                pcache->off, pcache->buffer, diff);
+        LFS2_ASSERT(err <= 0);
+        if (err) {
+            return err;
+        }
+
+        if (validate) {
+            // check data on disk
+            lfs2_cache_drop(lfs2, rcache);
+            int res = lfs2_bd_cmp(lfs2,
+                    NULL, rcache, diff,
+                    pcache->block, pcache->off, pcache->buffer, diff);
+            if (res < 0) {
+                return res;
+            }
+
+            if (res != LFS2_CMP_EQ) {
+                return LFS2_ERR_CORRUPT;
+            }
+        }
+
+        lfs2_cache_zero(lfs2, pcache);
+    }
+
+    return 0;
+}
+
+static int lfs2_bd_sync(lfs2_t *lfs2,
+        lfs2_cache_t *pcache, lfs2_cache_t *rcache, bool validate) {
+    lfs2_cache_drop(lfs2, rcache);
+
+    int err = lfs2_bd_flush(lfs2, pcache, rcache, validate);
+    if (err) {
+        return err;
+    }
+
+    err = lfs2->cfg->sync(lfs2->cfg);
+    LFS2_ASSERT(err <= 0);
+    return err;
+}
+
+static int lfs2_bd_prog(lfs2_t *lfs2,
+        lfs2_cache_t *pcache, lfs2_cache_t *rcache, bool validate,
+        lfs2_block_t block, lfs2_off_t off,
+        const void *buffer, lfs2_size_t size) {
+    const uint8_t *data = buffer;
+    LFS2_ASSERT(block != LFS2_BLOCK_NULL);
+    LFS2_ASSERT(off + size <= lfs2->cfg->block_size);
+
+    while (size > 0) {
+        if (block == pcache->block &&
+                off >= pcache->off &&
+                off < pcache->off + lfs2->cfg->cache_size) {
+            // already fits in pcache?
+            lfs2_size_t diff = lfs2_min(size,
+                    lfs2->cfg->cache_size - (off-pcache->off));
+            memcpy(&pcache->buffer[off-pcache->off], data, diff);
+
+            data += diff;
+            off += diff;
+            size -= diff;
+
+            pcache->size = lfs2_max(pcache->size, off - pcache->off);
+            if (pcache->size == lfs2->cfg->cache_size) {
+                // eagerly flush out pcache if we fill up
+                int err = lfs2_bd_flush(lfs2, pcache, rcache, validate);
+                if (err) {
+                    return err;
+                }
+            }
+
+            continue;
+        }
+
+        // pcache must have been flushed, either by programming and
+        // entire block or manually flushing the pcache
+        LFS2_ASSERT(pcache->block == LFS2_BLOCK_NULL);
+
+        // prepare pcache, first condition can no longer fail
+        pcache->block = block;
+        pcache->off = lfs2_aligndown(off, lfs2->cfg->prog_size);
+        pcache->size = 0;
+    }
+
+    return 0;
+}
+
+static int lfs2_bd_erase(lfs2_t *lfs2, lfs2_block_t block) {
+    LFS2_ASSERT(block < lfs2->cfg->block_count);
+    int err = lfs2->cfg->erase(lfs2->cfg, block);
+    LFS2_ASSERT(err <= 0);
+    return err;
+}
+
+
+/// Small type-level utilities ///
+// operations on block pairs
+static inline void lfs2_pair_swap(lfs2_block_t pair[2]) {
+    lfs2_block_t t = pair[0];
+    pair[0] = pair[1];
+    pair[1] = t;
+}
+
+static inline bool lfs2_pair_isnull(const lfs2_block_t pair[2]) {
+    return pair[0] == LFS2_BLOCK_NULL || pair[1] == LFS2_BLOCK_NULL;
+}
+
+static inline int lfs2_pair_cmp(
+        const lfs2_block_t paira[2],
+        const lfs2_block_t pairb[2]) {
+    return !(paira[0] == pairb[0] || paira[1] == pairb[1] ||
+             paira[0] == pairb[1] || paira[1] == pairb[0]);
+}
+
+static inline bool lfs2_pair_sync(
+        const lfs2_block_t paira[2],
+        const lfs2_block_t pairb[2]) {
+    return (paira[0] == pairb[0] && paira[1] == pairb[1]) ||
+           (paira[0] == pairb[1] && paira[1] == pairb[0]);
+}
+
+static inline void lfs2_pair_fromle32(lfs2_block_t pair[2]) {
+    pair[0] = lfs2_fromle32(pair[0]);
+    pair[1] = lfs2_fromle32(pair[1]);
+}
+
+static inline void lfs2_pair_tole32(lfs2_block_t pair[2]) {
+    pair[0] = lfs2_tole32(pair[0]);
+    pair[1] = lfs2_tole32(pair[1]);
+}
+
+// operations on 32-bit entry tags
+typedef uint32_t lfs2_tag_t;
+typedef int32_t lfs2_stag_t;
+
+#define LFS2_MKTAG(type, id, size) \
+    (((lfs2_tag_t)(type) << 20) | ((lfs2_tag_t)(id) << 10) | (lfs2_tag_t)(size))
+
+static inline bool lfs2_tag_isvalid(lfs2_tag_t tag) {
+    return !(tag & 0x80000000);
+}
+
+static inline bool lfs2_tag_isdelete(lfs2_tag_t tag) {
+    return ((int32_t)(tag << 22) >> 22) == -1;
+}
+
+static inline uint16_t lfs2_tag_type1(lfs2_tag_t tag) {
+    return (tag & 0x70000000) >> 20;
+}
+
+static inline uint16_t lfs2_tag_type3(lfs2_tag_t tag) {
+    return (tag & 0x7ff00000) >> 20;
+}
+
+static inline uint8_t lfs2_tag_chunk(lfs2_tag_t tag) {
+    return (tag & 0x0ff00000) >> 20;
+}
+
+static inline int8_t lfs2_tag_splice(lfs2_tag_t tag) {
+    return (int8_t)lfs2_tag_chunk(tag);
+}
+
+static inline uint16_t lfs2_tag_id(lfs2_tag_t tag) {
+    return (tag & 0x000ffc00) >> 10;
+}
+
+static inline lfs2_size_t lfs2_tag_size(lfs2_tag_t tag) {
+    return tag & 0x000003ff;
+}
+
+static inline lfs2_size_t lfs2_tag_dsize(lfs2_tag_t tag) {
+    return sizeof(tag) + lfs2_tag_size(tag + lfs2_tag_isdelete(tag));
+}
+
+// operations on attributes in attribute lists
+struct lfs2_mattr {
+    lfs2_tag_t tag;
+    const void *buffer;
+};
+
+struct lfs2_diskoff {
+    lfs2_block_t block;
+    lfs2_off_t off;
+};
+
+#define LFS2_MKATTRS(...) \
+    (struct lfs2_mattr[]){__VA_ARGS__}, \
+    sizeof((struct lfs2_mattr[]){__VA_ARGS__}) / sizeof(struct lfs2_mattr)
+
+// operations on global state
+static inline void lfs2_gstate_xor(struct lfs2_gstate *a,
+        const struct lfs2_gstate *b) {
+    for (int i = 0; i < 3; i++) {
+        ((uint32_t*)a)[i] ^= ((const uint32_t*)b)[i];
+    }
+}
+
+static inline bool lfs2_gstate_iszero(const struct lfs2_gstate *a) {
+    for (int i = 0; i < 3; i++) {
+        if (((uint32_t*)a)[i] != 0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+static inline bool lfs2_gstate_hasorphans(const struct lfs2_gstate *a) {
+    return lfs2_tag_size(a->tag);
+}
+
+static inline uint8_t lfs2_gstate_getorphans(const struct lfs2_gstate *a) {
+    return lfs2_tag_size(a->tag);
+}
+
+static inline bool lfs2_gstate_hasmove(const struct lfs2_gstate *a) {
+    return lfs2_tag_type1(a->tag);
+}
+
+static inline bool lfs2_gstate_hasmovehere(const struct lfs2_gstate *a,
+        const lfs2_block_t *pair) {
+    return lfs2_tag_type1(a->tag) && lfs2_pair_cmp(a->pair, pair) == 0;
+}
+
+static inline void lfs2_gstate_xororphans(struct lfs2_gstate *a,
+        const struct lfs2_gstate *b, bool orphans) {
+    a->tag ^= LFS2_MKTAG(0x800, 0, 0) & (b->tag ^ ((uint32_t)orphans << 31));
+}
+
+static inline void lfs2_gstate_xormove(struct lfs2_gstate *a,
+        const struct lfs2_gstate *b, uint16_t id, const lfs2_block_t pair[2]) {
+    a->tag ^= LFS2_MKTAG(0x7ff, 0x3ff, 0) & (b->tag ^ (
+            (id != 0x3ff) ? LFS2_MKTAG(LFS2_TYPE_DELETE, id, 0) : 0));
+    a->pair[0] ^= b->pair[0] ^ ((id != 0x3ff) ? pair[0] : 0);
+    a->pair[1] ^= b->pair[1] ^ ((id != 0x3ff) ? pair[1] : 0);
+}
+
+static inline void lfs2_gstate_fromle32(struct lfs2_gstate *a) {
+    a->tag     = lfs2_fromle32(a->tag);
+    a->pair[0] = lfs2_fromle32(a->pair[0]);
+    a->pair[1] = lfs2_fromle32(a->pair[1]);
+}
+
+static inline void lfs2_gstate_tole32(struct lfs2_gstate *a) {
+    a->tag     = lfs2_tole32(a->tag);
+    a->pair[0] = lfs2_tole32(a->pair[0]);
+    a->pair[1] = lfs2_tole32(a->pair[1]);
+}
+
+// other endianness operations
+static void lfs2_ctz_fromle32(struct lfs2_ctz *ctz) {
+    ctz->head = lfs2_fromle32(ctz->head);
+    ctz->size = lfs2_fromle32(ctz->size);
+}
+
+static void lfs2_ctz_tole32(struct lfs2_ctz *ctz) {
+    ctz->head = lfs2_tole32(ctz->head);
+    ctz->size = lfs2_tole32(ctz->size);
+}
+
+static inline void lfs2_superblock_fromle32(lfs2_superblock_t *superblock) {
+    superblock->version     = lfs2_fromle32(superblock->version);
+    superblock->block_size  = lfs2_fromle32(superblock->block_size);
+    superblock->block_count = lfs2_fromle32(superblock->block_count);
+    superblock->name_max    = lfs2_fromle32(superblock->name_max);
+    superblock->file_max    = lfs2_fromle32(superblock->file_max);
+    superblock->attr_max    = lfs2_fromle32(superblock->attr_max);
+}
+
+static inline void lfs2_superblock_tole32(lfs2_superblock_t *superblock) {
+    superblock->version     = lfs2_tole32(superblock->version);
+    superblock->block_size  = lfs2_tole32(superblock->block_size);
+    superblock->block_count = lfs2_tole32(superblock->block_count);
+    superblock->name_max    = lfs2_tole32(superblock->name_max);
+    superblock->file_max    = lfs2_tole32(superblock->file_max);
+    superblock->attr_max    = lfs2_tole32(superblock->attr_max);
+}
+
+
+/// Internal operations predeclared here ///
+static int lfs2_dir_commit(lfs2_t *lfs2, lfs2_mdir_t *dir,
+        const struct lfs2_mattr *attrs, int attrcount);
+static int lfs2_dir_compact(lfs2_t *lfs2,
+        lfs2_mdir_t *dir, const struct lfs2_mattr *attrs, int attrcount,
+        lfs2_mdir_t *source, uint16_t begin, uint16_t end);
+static int lfs2_file_outline(lfs2_t *lfs2, lfs2_file_t *file);
+static int lfs2_file_flush(lfs2_t *lfs2, lfs2_file_t *file);
+static void lfs2_fs_preporphans(lfs2_t *lfs2, int8_t orphans);
+static void lfs2_fs_prepmove(lfs2_t *lfs2,
+        uint16_t id, const lfs2_block_t pair[2]);
+static int lfs2_fs_pred(lfs2_t *lfs2, const lfs2_block_t dir[2],
+        lfs2_mdir_t *pdir);
+static lfs2_stag_t lfs2_fs_parent(lfs2_t *lfs2, const lfs2_block_t dir[2],
+        lfs2_mdir_t *parent);
+static int lfs2_fs_relocate(lfs2_t *lfs2,
+        const lfs2_block_t oldpair[2], lfs2_block_t newpair[2]);
+static int lfs2_fs_forceconsistency(lfs2_t *lfs2);
+static int lfs2_deinit(lfs2_t *lfs2);
+#ifdef LFS2_MIGRATE
+static int lfs21_traverse(lfs2_t *lfs2,
+        int (*cb)(void*, lfs2_block_t), void *data);
+#endif
+
+/// Block allocator ///
+static int lfs2_alloc_lookahead(void *p, lfs2_block_t block) {
+    lfs2_t *lfs2 = (lfs2_t*)p;
+    lfs2_block_t off = ((block - lfs2->free.off)
+            + lfs2->cfg->block_count) % lfs2->cfg->block_count;
+
+    if (off < lfs2->free.size) {
+        lfs2->free.buffer[off / 32] |= 1U << (off % 32);
+    }
+
+    return 0;
+}
+
+static int lfs2_alloc(lfs2_t *lfs2, lfs2_block_t *block) {
+    while (true) {
+        while (lfs2->free.i != lfs2->free.size) {
+            lfs2_block_t off = lfs2->free.i;
+            lfs2->free.i += 1;
+            lfs2->free.ack -= 1;
+
+            if (!(lfs2->free.buffer[off / 32] & (1U << (off % 32)))) {
+                // found a free block
+                *block = (lfs2->free.off + off) % lfs2->cfg->block_count;
+
+                // eagerly find next off so an alloc ack can
+                // discredit old lookahead blocks
+                while (lfs2->free.i != lfs2->free.size &&
+                        (lfs2->free.buffer[lfs2->free.i / 32]
+                            & (1U << (lfs2->free.i % 32)))) {
+                    lfs2->free.i += 1;
+                    lfs2->free.ack -= 1;
+                }
+
+                return 0;
+            }
+        }
+
+        // check if we have looked at all blocks since last ack
+        if (lfs2->free.ack == 0) {
+            LFS2_ERROR("No more free space %"PRIu32,
+                    lfs2->free.i + lfs2->free.off);
+            return LFS2_ERR_NOSPC;
+        }
+
+        lfs2->free.off = (lfs2->free.off + lfs2->free.size)
+                % lfs2->cfg->block_count;
+        lfs2->free.size = lfs2_min(8*lfs2->cfg->lookahead_size, lfs2->free.ack);
+        lfs2->free.i = 0;
+
+        // find mask of free blocks from tree
+        memset(lfs2->free.buffer, 0, lfs2->cfg->lookahead_size);
+        int err = lfs2_fs_traverse(lfs2, lfs2_alloc_lookahead, lfs2);
+        if (err) {
+            return err;
+        }
+    }
+}
+
+static void lfs2_alloc_ack(lfs2_t *lfs2) {
+    lfs2->free.ack = lfs2->cfg->block_count;
+}
+
+
+/// Metadata pair and directory operations ///
+static lfs2_stag_t lfs2_dir_getslice(lfs2_t *lfs2, const lfs2_mdir_t *dir,
+        lfs2_tag_t gmask, lfs2_tag_t gtag,
+        lfs2_off_t goff, void *gbuffer, lfs2_size_t gsize) {
+    lfs2_off_t off = dir->off;
+    lfs2_tag_t ntag = dir->etag;
+    lfs2_stag_t gdiff = 0;
+
+    if (lfs2_gstate_hasmovehere(&lfs2->gstate, dir->pair) &&
+            lfs2_tag_id(gtag) <= lfs2_tag_id(lfs2->gstate.tag)) {
+        // synthetic moves
+        gdiff -= LFS2_MKTAG(0, 1, 0);
+    }
+
+    // iterate over dir block backwards (for faster lookups)
+    while (off >= sizeof(lfs2_tag_t) + lfs2_tag_dsize(ntag)) {
+        off -= lfs2_tag_dsize(ntag);
+        lfs2_tag_t tag = ntag;
+        int err = lfs2_bd_read(lfs2,
+                NULL, &lfs2->rcache, sizeof(ntag),
+                dir->pair[0], off, &ntag, sizeof(ntag));
+        if (err) {
+            return err;
+        }
+
+        ntag = (lfs2_frombe32(ntag) ^ tag) & 0x7fffffff;
+
+        if (lfs2_tag_id(gmask) != 0 &&
+                lfs2_tag_type1(tag) == LFS2_TYPE_SPLICE &&
+                lfs2_tag_id(tag) <= lfs2_tag_id(gtag - gdiff)) {
+            if (tag == (LFS2_MKTAG(LFS2_TYPE_CREATE, 0, 0) |
+                    (LFS2_MKTAG(0, 0x3ff, 0) & (gtag - gdiff)))) {
+                // found where we were created
+                return LFS2_ERR_NOENT;
+            }
+
+            // move around splices
+            gdiff += LFS2_MKTAG(0, lfs2_tag_splice(tag), 0);
+        }
+
+        if ((gmask & tag) == (gmask & (gtag - gdiff))) {
+            if (lfs2_tag_isdelete(tag)) {
+                return LFS2_ERR_NOENT;
+            }
+
+            lfs2_size_t diff = lfs2_min(lfs2_tag_size(tag), gsize);
+            err = lfs2_bd_read(lfs2,
+                    NULL, &lfs2->rcache, diff,
+                    dir->pair[0], off+sizeof(tag)+goff, gbuffer, diff);
+            if (err) {
+                return err;
+            }
+
+            memset((uint8_t*)gbuffer + diff, 0, gsize - diff);
+
+            return tag + gdiff;
+        }
+    }
+
+    return LFS2_ERR_NOENT;
+}
+
+static lfs2_stag_t lfs2_dir_get(lfs2_t *lfs2, const lfs2_mdir_t *dir,
+        lfs2_tag_t gmask, lfs2_tag_t gtag, void *buffer) {
+    return lfs2_dir_getslice(lfs2, dir,
+            gmask, gtag,
+            0, buffer, lfs2_tag_size(gtag));
+}
+
+static int lfs2_dir_getread(lfs2_t *lfs2, const lfs2_mdir_t *dir,
+        const lfs2_cache_t *pcache, lfs2_cache_t *rcache, lfs2_size_t hint,
+        lfs2_tag_t gmask, lfs2_tag_t gtag,
+        lfs2_off_t off, void *buffer, lfs2_size_t size) {
+    uint8_t *data = buffer;
+    if (off+size > lfs2->cfg->block_size) {
+        return LFS2_ERR_CORRUPT;
+    }
+
+    while (size > 0) {
+        lfs2_size_t diff = size;
+
+        if (pcache && pcache->block == LFS2_BLOCK_INLINE &&
+                off < pcache->off + pcache->size) {
+            if (off >= pcache->off) {
+                // is already in pcache?
+                diff = lfs2_min(diff, pcache->size - (off-pcache->off));
+                memcpy(data, &pcache->buffer[off-pcache->off], diff);
+
+                data += diff;
+                off += diff;
+                size -= diff;
+                continue;
+            }
+
+            // pcache takes priority
+            diff = lfs2_min(diff, pcache->off-off);
+        }
+
+        if (rcache->block == LFS2_BLOCK_INLINE &&
+                off < rcache->off + rcache->size) {
+            if (off >= rcache->off) {
+                // is already in rcache?
+                diff = lfs2_min(diff, rcache->size - (off-rcache->off));
+                memcpy(data, &rcache->buffer[off-rcache->off], diff);
+
+                data += diff;
+                off += diff;
+                size -= diff;
+                continue;
+            }
+
+            // rcache takes priority
+            diff = lfs2_min(diff, rcache->off-off);
+        }
+
+        // load to cache, first condition can no longer fail
+        rcache->block = LFS2_BLOCK_INLINE;
+        rcache->off = lfs2_aligndown(off, lfs2->cfg->read_size);
+        rcache->size = lfs2_min(lfs2_alignup(off+hint, lfs2->cfg->read_size),
+                lfs2->cfg->cache_size);
+        int err = lfs2_dir_getslice(lfs2, dir, gmask, gtag,
+                rcache->off, rcache->buffer, rcache->size);
+        if (err < 0) {
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_traverse_filter(void *p,
+        lfs2_tag_t tag, const void *buffer) {
+    lfs2_tag_t *filtertag = p;
+    (void)buffer;
+
+    // which mask depends on unique bit in tag structure
+    uint32_t mask = (tag & LFS2_MKTAG(0x100, 0, 0))
+            ? LFS2_MKTAG(0x7ff, 0x3ff, 0)
+            : LFS2_MKTAG(0x700, 0x3ff, 0);
+
+    // check for redundancy
+    if ((mask & tag) == (mask & *filtertag) ||
+            lfs2_tag_isdelete(*filtertag) ||
+            (LFS2_MKTAG(0x7ff, 0x3ff, 0) & tag) == (
+                LFS2_MKTAG(LFS2_TYPE_DELETE, 0, 0) |
+                    (LFS2_MKTAG(0, 0x3ff, 0) & *filtertag))) {
+        return true;
+    }
+
+    // check if we need to adjust for created/deleted tags
+    if (lfs2_tag_type1(tag) == LFS2_TYPE_SPLICE &&
+            lfs2_tag_id(tag) <= lfs2_tag_id(*filtertag)) {
+        *filtertag += LFS2_MKTAG(0, lfs2_tag_splice(tag), 0);
+    }
+
+    return false;
+}
+
+static int lfs2_dir_traverse(lfs2_t *lfs2,
+        const lfs2_mdir_t *dir, lfs2_off_t off, lfs2_tag_t ptag,
+        const struct lfs2_mattr *attrs, int attrcount, bool hasseenmove,
+        lfs2_tag_t tmask, lfs2_tag_t ttag,
+        uint16_t begin, uint16_t end, int16_t diff,
+        int (*cb)(void *data, lfs2_tag_t tag, const void *buffer), void *data) {
+    // iterate over directory and attrs
+    while (true) {
+        lfs2_tag_t tag;
+        const void *buffer;
+        struct lfs2_diskoff disk;
+        if (off+lfs2_tag_dsize(ptag) < dir->off) {
+            off += lfs2_tag_dsize(ptag);
+            int err = lfs2_bd_read(lfs2,
+                    NULL, &lfs2->rcache, sizeof(tag),
+                    dir->pair[0], off, &tag, sizeof(tag));
+            if (err) {
+                return err;
+            }
+
+            tag = (lfs2_frombe32(tag) ^ ptag) | 0x80000000;
+            disk.block = dir->pair[0];
+            disk.off = off+sizeof(lfs2_tag_t);
+            buffer = &disk;
+            ptag = tag;
+        } else if (attrcount > 0) {
+            tag = attrs[0].tag;
+            buffer = attrs[0].buffer;
+            attrs += 1;
+            attrcount -= 1;
+        } else if (!hasseenmove &&
+                lfs2_gstate_hasmovehere(&lfs2->gpending, dir->pair)) {
+            // Wait, we have pending move? Handle this here (we need to
+            // or else we risk letting moves fall out of date)
+            tag = lfs2->gpending.tag & LFS2_MKTAG(0x7ff, 0x3ff, 0);
+            buffer = NULL;
+            hasseenmove = true;
+        } else {
+            return 0;
+        }
+
+        lfs2_tag_t mask = LFS2_MKTAG(0x7ff, 0, 0);
+        if ((mask & tmask & tag) != (mask & tmask & ttag)) {
+            continue;
+        }
+
+        // do we need to filter? inlining the filtering logic here allows
+        // for some minor optimizations
+        if (lfs2_tag_id(tmask) != 0) {
+            // scan for duplicates and update tag based on creates/deletes
+            int filter = lfs2_dir_traverse(lfs2,
+                    dir, off, ptag, attrs, attrcount, hasseenmove,
+                    0, 0, 0, 0, 0,
+                    lfs2_dir_traverse_filter, &tag);
+            if (filter < 0) {
+                return filter;
+            }
+
+            if (filter) {
+                continue;
+            }
+
+            // in filter range?
+            if (!(lfs2_tag_id(tag) >= begin && lfs2_tag_id(tag) < end)) {
+                continue;
+            }
+        }
+
+        // handle special cases for mcu-side operations
+        if (lfs2_tag_type3(tag) == LFS2_FROM_NOOP) {
+            // do nothing
+        } else if (lfs2_tag_type3(tag) == LFS2_FROM_MOVE) {
+            uint16_t fromid = lfs2_tag_size(tag);
+            uint16_t toid = lfs2_tag_id(tag);
+            int err = lfs2_dir_traverse(lfs2,
+                    buffer, 0, LFS2_BLOCK_NULL, NULL, 0, true,
+                    LFS2_MKTAG(0x600, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_STRUCT, 0, 0),
+                    fromid, fromid+1, toid-fromid+diff,
+                    cb, data);
+            if (err) {
+                return err;
+            }
+        } else if (lfs2_tag_type3(tag) == LFS2_FROM_USERATTRS) {
+            for (unsigned i = 0; i < lfs2_tag_size(tag); i++) {
+                const struct lfs2_attr *a = buffer;
+                int err = cb(data, LFS2_MKTAG(LFS2_TYPE_USERATTR + a[i].type,
+                        lfs2_tag_id(tag) + diff, a[i].size), a[i].buffer);
+                if (err) {
+                    return err;
+                }
+            }
+        } else {
+            int err = cb(data, tag + LFS2_MKTAG(0, diff, 0), buffer);
+            if (err) {
+                return err;
+            }
+        }
+    }
+}
+
+static lfs2_stag_t lfs2_dir_fetchmatch(lfs2_t *lfs2,
+        lfs2_mdir_t *dir, const lfs2_block_t pair[2],
+        lfs2_tag_t fmask, lfs2_tag_t ftag, uint16_t *id,
+        int (*cb)(void *data, lfs2_tag_t tag, const void *buffer), void *data) {
+    // we can find tag very efficiently during a fetch, since we're already
+    // scanning the entire directory
+    lfs2_stag_t besttag = -1;
+
+    // find the block with the most recent revision
+    uint32_t revs[2] = {0, 0};
+    int r = 0;
+    for (int i = 0; i < 2; i++) {
+        int err = lfs2_bd_read(lfs2,
+                NULL, &lfs2->rcache, sizeof(revs[i]),
+                pair[i], 0, &revs[i], sizeof(revs[i]));
+        revs[i] = lfs2_fromle32(revs[i]);
+        if (err && err != LFS2_ERR_CORRUPT) {
+            return err;
+        }
+
+        if (err != LFS2_ERR_CORRUPT &&
+                lfs2_scmp(revs[i], revs[(i+1)%2]) > 0) {
+            r = i;
+        }
+    }
+
+    dir->pair[0] = pair[(r+0)%2];
+    dir->pair[1] = pair[(r+1)%2];
+    dir->rev = revs[(r+0)%2];
+    dir->off = 0; // nonzero = found some commits
+
+    // now scan tags to fetch the actual dir and find possible match
+    for (int i = 0; i < 2; i++) {
+        lfs2_off_t off = 0;
+        lfs2_tag_t ptag = LFS2_BLOCK_NULL;
+
+        uint16_t tempcount = 0;
+        lfs2_block_t temptail[2] = {LFS2_BLOCK_NULL, LFS2_BLOCK_NULL};
+        bool tempsplit = false;
+        lfs2_stag_t tempbesttag = besttag;
+
+        dir->rev = lfs2_tole32(dir->rev);
+        uint32_t crc = lfs2_crc(LFS2_BLOCK_NULL, &dir->rev, sizeof(dir->rev));
+        dir->rev = lfs2_fromle32(dir->rev);
+
+        while (true) {
+            // extract next tag
+            lfs2_tag_t tag;
+            off += lfs2_tag_dsize(ptag);
+            int err = lfs2_bd_read(lfs2,
+                    NULL, &lfs2->rcache, lfs2->cfg->block_size,
+                    dir->pair[0], off, &tag, sizeof(tag));
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    // can't continue?
+                    dir->erased = false;
+                    break;
+                }
+                return err;
+            }
+
+            crc = lfs2_crc(crc, &tag, sizeof(tag));
+            tag = lfs2_frombe32(tag) ^ ptag;
+
+            // next commit not yet programmed or we're not in valid range
+            if (!lfs2_tag_isvalid(tag) ||
+                    off + lfs2_tag_dsize(tag) > lfs2->cfg->block_size) {
+                dir->erased = (lfs2_tag_type1(ptag) == LFS2_TYPE_CRC &&
+                        dir->off % lfs2->cfg->prog_size == 0);
+                break;
+            }
+
+            ptag = tag;
+
+            if (lfs2_tag_type1(tag) == LFS2_TYPE_CRC) {
+                // check the crc attr
+                uint32_t dcrc;
+                err = lfs2_bd_read(lfs2,
+                        NULL, &lfs2->rcache, lfs2->cfg->block_size,
+                        dir->pair[0], off+sizeof(tag), &dcrc, sizeof(dcrc));
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        dir->erased = false;
+                        break;
+                    }
+                    return err;
+                }
+                dcrc = lfs2_fromle32(dcrc);
+
+                if (crc != dcrc) {
+                    dir->erased = false;
+                    break;
+                }
+
+                // reset the next bit if we need to
+                ptag ^= (lfs2_tag_t)(lfs2_tag_chunk(tag) & 1U) << 31;
+
+                // toss our crc into the filesystem seed for
+                // pseudorandom numbers
+                lfs2->seed ^= crc;
+
+                // update with what's found so far
+                besttag = tempbesttag;
+                dir->off = off + lfs2_tag_dsize(tag);
+                dir->etag = ptag;
+                dir->count = tempcount;
+                dir->tail[0] = temptail[0];
+                dir->tail[1] = temptail[1];
+                dir->split = tempsplit;
+
+                // reset crc
+                crc = LFS2_BLOCK_NULL;
+                continue;
+            }
+
+            // crc the entry first, hopefully leaving it in the cache
+            for (lfs2_off_t j = sizeof(tag); j < lfs2_tag_dsize(tag); j++) {
+                uint8_t dat;
+                err = lfs2_bd_read(lfs2,
+                        NULL, &lfs2->rcache, lfs2->cfg->block_size,
+                        dir->pair[0], off+j, &dat, 1);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        dir->erased = false;
+                        break;
+                    }
+                    return err;
+                }
+
+                crc = lfs2_crc(crc, &dat, 1);
+            }
+
+            // directory modification tags?
+            if (lfs2_tag_type1(tag) == LFS2_TYPE_NAME) {
+                // increase count of files if necessary
+                if (lfs2_tag_id(tag) >= tempcount) {
+                    tempcount = lfs2_tag_id(tag) + 1;
+                }
+            } else if (lfs2_tag_type1(tag) == LFS2_TYPE_SPLICE) {
+                tempcount += lfs2_tag_splice(tag);
+
+                if (tag == (LFS2_MKTAG(LFS2_TYPE_DELETE, 0, 0) |
+                        (LFS2_MKTAG(0, 0x3ff, 0) & tempbesttag))) {
+                    tempbesttag |= 0x80000000;
+                } else if (tempbesttag != -1 &&
+                        lfs2_tag_id(tag) <= lfs2_tag_id(tempbesttag)) {
+                    tempbesttag += LFS2_MKTAG(0, lfs2_tag_splice(tag), 0);
+                }
+            } else if (lfs2_tag_type1(tag) == LFS2_TYPE_TAIL) {
+                tempsplit = (lfs2_tag_chunk(tag) & 1);
+
+                err = lfs2_bd_read(lfs2,
+                        NULL, &lfs2->rcache, lfs2->cfg->block_size,
+                        dir->pair[0], off+sizeof(tag), &temptail, 8);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        dir->erased = false;
+                        break;
+                    }
+                }
+                lfs2_pair_fromle32(temptail);
+            }
+
+            // found a match for our fetcher?
+            if ((fmask & tag) == (fmask & ftag)) {
+                int res = cb(data, tag, &(struct lfs2_diskoff){
+                        dir->pair[0], off+sizeof(tag)});
+                if (res < 0) {
+                    if (res == LFS2_ERR_CORRUPT) {
+                        dir->erased = false;
+                        break;
+                    }
+                    return res;
+                }
+
+                if (res == LFS2_CMP_EQ) {
+                    // found a match
+                    tempbesttag = tag;
+                } else if (res == LFS2_CMP_GT &&
+                        lfs2_tag_id(tag) <= lfs2_tag_id(tempbesttag)) {
+                    // found a greater match, keep track to keep things sorted
+                    tempbesttag = tag | 0x80000000;
+                }
+            }
+        }
+
+        // consider what we have good enough
+        if (dir->off > 0) {
+            // synthetic move
+            if (lfs2_gstate_hasmovehere(&lfs2->gstate, dir->pair)) {
+                if (lfs2_tag_id(lfs2->gstate.tag) == lfs2_tag_id(besttag)) {
+                    besttag |= 0x80000000;
+                } else if (besttag != -1 &&
+                        lfs2_tag_id(lfs2->gstate.tag) < lfs2_tag_id(besttag)) {
+                    besttag -= LFS2_MKTAG(0, 1, 0);
+                }
+            }
+
+            // found tag? or found best id?
+            if (id) {
+                *id = lfs2_min(lfs2_tag_id(besttag), dir->count);
+            }
+
+            if (lfs2_tag_isvalid(besttag)) {
+                return besttag;
+            } else if (lfs2_tag_id(besttag) < dir->count) {
+                return LFS2_ERR_NOENT;
+            } else {
+                return 0;
+            }
+        }
+
+        // failed, try the other block?
+        lfs2_pair_swap(dir->pair);
+        dir->rev = revs[(r+1)%2];
+    }
+
+    LFS2_ERROR("Corrupted dir pair at %"PRIx32" %"PRIx32,
+            dir->pair[0], dir->pair[1]);
+    return LFS2_ERR_CORRUPT;
+}
+
+static int lfs2_dir_fetch(lfs2_t *lfs2,
+        lfs2_mdir_t *dir, const lfs2_block_t pair[2]) {
+    // note, mask=-1, tag=0 can never match a tag since this
+    // pattern has the invalid bit set
+    return (int)lfs2_dir_fetchmatch(lfs2, dir, pair, -1, 0, NULL, NULL, NULL);
+}
+
+static int lfs2_dir_getgstate(lfs2_t *lfs2, const lfs2_mdir_t *dir,
+        struct lfs2_gstate *gstate) {
+    struct lfs2_gstate temp;
+    lfs2_stag_t res = lfs2_dir_get(lfs2, dir, LFS2_MKTAG(0x7ff, 0, 0),
+            LFS2_MKTAG(LFS2_TYPE_MOVESTATE, 0, sizeof(temp)), &temp);
+    if (res < 0 && res != LFS2_ERR_NOENT) {
+        return res;
+    }
+
+    if (res != LFS2_ERR_NOENT) {
+        // xor together to find resulting gstate
+        lfs2_gstate_fromle32(&temp);
+        lfs2_gstate_xor(gstate, &temp);
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_getinfo(lfs2_t *lfs2, lfs2_mdir_t *dir,
+        uint16_t id, struct lfs2_info *info) {
+    if (id == 0x3ff) {
+        // special case for root
+        strcpy(info->name, "/");
+        info->type = LFS2_TYPE_DIR;
+        return 0;
+    }
+
+    lfs2_stag_t tag = lfs2_dir_get(lfs2, dir, LFS2_MKTAG(0x780, 0x3ff, 0),
+            LFS2_MKTAG(LFS2_TYPE_NAME, id, lfs2->name_max+1), info->name);
+    if (tag < 0) {
+        return (int)tag;
+    }
+
+    info->type = lfs2_tag_type3(tag);
+
+    struct lfs2_ctz ctz;
+    tag = lfs2_dir_get(lfs2, dir, LFS2_MKTAG(0x700, 0x3ff, 0),
+            LFS2_MKTAG(LFS2_TYPE_STRUCT, id, sizeof(ctz)), &ctz);
+    if (tag < 0) {
+        return (int)tag;
+    }
+    lfs2_ctz_fromle32(&ctz);
+
+    if (lfs2_tag_type3(tag) == LFS2_TYPE_CTZSTRUCT) {
+        info->size = ctz.size;
+    } else if (lfs2_tag_type3(tag) == LFS2_TYPE_INLINESTRUCT) {
+        info->size = lfs2_tag_size(tag);
+    }
+
+    return 0;
+}
+
+struct lfs2_dir_find_match {
+    lfs2_t *lfs2;
+    const void *name;
+    lfs2_size_t size;
+};
+
+static int lfs2_dir_find_match(void *data,
+        lfs2_tag_t tag, const void *buffer) {
+    struct lfs2_dir_find_match *name = data;
+    lfs2_t *lfs2 = name->lfs2;
+    const struct lfs2_diskoff *disk = buffer;
+
+    // compare with disk
+    lfs2_size_t diff = lfs2_min(name->size, lfs2_tag_size(tag));
+    int res = lfs2_bd_cmp(lfs2,
+            NULL, &lfs2->rcache, diff,
+            disk->block, disk->off, name->name, diff);
+    if (res != LFS2_CMP_EQ) {
+        return res;
+    }
+
+    // only equal if our size is still the same
+    if (name->size != lfs2_tag_size(tag)) {
+        return (name->size < lfs2_tag_size(tag)) ? LFS2_CMP_LT : LFS2_CMP_GT;
+    }
+
+    // found a match!
+    return LFS2_CMP_EQ;
+}
+
+static lfs2_stag_t lfs2_dir_find(lfs2_t *lfs2, lfs2_mdir_t *dir,
+        const char **path, uint16_t *id) {
+    // we reduce path to a single name if we can find it
+    const char *name = *path;
+    if (id) {
+        *id = 0x3ff;
+    }
+
+    // default to root dir
+    lfs2_stag_t tag = LFS2_MKTAG(LFS2_TYPE_DIR, 0x3ff, 0);
+    dir->tail[0] = lfs2->root[0];
+    dir->tail[1] = lfs2->root[1];
+
+    while (true) {
+nextname:
+        // skip slashes
+        name += strspn(name, "/");
+        lfs2_size_t namelen = strcspn(name, "/");
+
+        // skip '.' and root '..'
+        if ((namelen == 1 && memcmp(name, ".", 1) == 0) ||
+            (namelen == 2 && memcmp(name, "..", 2) == 0)) {
+            name += namelen;
+            goto nextname;
+        }
+
+        // skip if matched by '..' in name
+        const char *suffix = name + namelen;
+        lfs2_size_t sufflen;
+        int depth = 1;
+        while (true) {
+            suffix += strspn(suffix, "/");
+            sufflen = strcspn(suffix, "/");
+            if (sufflen == 0) {
+                break;
+            }
+
+            if (sufflen == 2 && memcmp(suffix, "..", 2) == 0) {
+                depth -= 1;
+                if (depth == 0) {
+                    name = suffix + sufflen;
+                    goto nextname;
+                }
+            } else {
+                depth += 1;
+            }
+
+            suffix += sufflen;
+        }
+
+        // found path
+        if (name[0] == '\0') {
+            return tag;
+        }
+
+        // update what we've found so far
+        *path = name;
+
+        // only continue if we hit a directory
+        if (lfs2_tag_type3(tag) != LFS2_TYPE_DIR) {
+            return LFS2_ERR_NOTDIR;
+        }
+
+        // grab the entry data
+        if (lfs2_tag_id(tag) != 0x3ff) {
+            lfs2_stag_t res = lfs2_dir_get(lfs2, dir, LFS2_MKTAG(0x700, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_STRUCT, lfs2_tag_id(tag), 8), dir->tail);
+            if (res < 0) {
+                return res;
+            }
+            lfs2_pair_fromle32(dir->tail);
+        }
+
+        // find entry matching name
+        while (true) {
+            tag = lfs2_dir_fetchmatch(lfs2, dir, dir->tail,
+                    LFS2_MKTAG(0x780, 0, 0),
+                    LFS2_MKTAG(LFS2_TYPE_NAME, 0, namelen),
+                     // are we last name?
+                    (strchr(name, '/') == NULL) ? id : NULL,
+                    lfs2_dir_find_match, &(struct lfs2_dir_find_match){
+                        lfs2, name, namelen});
+            if (tag < 0) {
+                return tag;
+            }
+
+            if (tag) {
+                break;
+            }
+
+            if (!dir->split) {
+                return LFS2_ERR_NOENT;
+            }
+        }
+
+        // to next name
+        name += namelen;
+    }
+}
+
+// commit logic
+struct lfs2_commit {
+    lfs2_block_t block;
+    lfs2_off_t off;
+    lfs2_tag_t ptag;
+    uint32_t crc;
+
+    lfs2_off_t begin;
+    lfs2_off_t end;
+};
+
+static int lfs2_dir_commitprog(lfs2_t *lfs2, struct lfs2_commit *commit,
+        const void *buffer, lfs2_size_t size) {
+    int err = lfs2_bd_prog(lfs2,
+            &lfs2->pcache, &lfs2->rcache, false,
+            commit->block, commit->off ,
+            (const uint8_t*)buffer, size);
+    if (err) {
+        return err;
+    }
+
+    commit->crc = lfs2_crc(commit->crc, buffer, size);
+    commit->off += size;
+    return 0;
+}
+
+static int lfs2_dir_commitattr(lfs2_t *lfs2, struct lfs2_commit *commit,
+        lfs2_tag_t tag, const void *buffer) {
+    // check if we fit
+    lfs2_size_t dsize = lfs2_tag_dsize(tag);
+    if (commit->off + dsize > commit->end) {
+        return LFS2_ERR_NOSPC;
+    }
+
+    // write out tag
+    lfs2_tag_t ntag = lfs2_tobe32((tag & 0x7fffffff) ^ commit->ptag);
+    int err = lfs2_dir_commitprog(lfs2, commit, &ntag, sizeof(ntag));
+    if (err) {
+        return err;
+    }
+
+    if (!(tag & 0x80000000)) {
+        // from memory
+        err = lfs2_dir_commitprog(lfs2, commit, buffer, dsize-sizeof(tag));
+        if (err) {
+            return err;
+        }
+    } else {
+        // from disk
+        const struct lfs2_diskoff *disk = buffer;
+        for (lfs2_off_t i = 0; i < dsize-sizeof(tag); i++) {
+            // rely on caching to make this efficient
+            uint8_t dat;
+            err = lfs2_bd_read(lfs2,
+                    NULL, &lfs2->rcache, dsize-sizeof(tag)-i,
+                    disk->block, disk->off+i, &dat, 1);
+            if (err) {
+                return err;
+            }
+
+            err = lfs2_dir_commitprog(lfs2, commit, &dat, 1);
+            if (err) {
+                return err;
+            }
+        }
+    }
+
+    commit->ptag = tag & 0x7fffffff;
+    return 0;
+}
+
+static int lfs2_dir_commitcrc(lfs2_t *lfs2, struct lfs2_commit *commit) {
+    // align to program units
+    const lfs2_off_t off1 = commit->off + sizeof(lfs2_tag_t);
+    const lfs2_off_t end = lfs2_alignup(off1 + sizeof(uint32_t),
+            lfs2->cfg->prog_size);
+
+    // create crc tags to fill up remainder of commit, note that
+    // padding is not crcd, which lets fetches skip padding but
+    // makes committing a bit more complicated
+    while (commit->off < end) {
+        lfs2_off_t off = commit->off + sizeof(lfs2_tag_t);
+        lfs2_off_t noff = lfs2_min(end - off, 0x3fe) + off;
+        if (noff < end) {
+            noff = lfs2_min(noff, end - 2*sizeof(uint32_t));
+        }
+
+        // read erased state from next program unit
+        lfs2_tag_t tag = LFS2_BLOCK_NULL;
+        int err = lfs2_bd_read(lfs2,
+                NULL, &lfs2->rcache, sizeof(tag),
+                commit->block, noff, &tag, sizeof(tag));
+        if (err && err != LFS2_ERR_CORRUPT) {
+            return err;
+        }
+
+        // build crc tag
+        bool reset = ~lfs2_frombe32(tag) >> 31;
+        tag = LFS2_MKTAG(LFS2_TYPE_CRC + reset, 0x3ff, noff - off);
+
+        // write out crc
+        uint32_t footer[2];
+        footer[0] = lfs2_tobe32(tag ^ commit->ptag);
+        commit->crc = lfs2_crc(commit->crc, &footer[0], sizeof(footer[0]));
+        footer[1] = lfs2_tole32(commit->crc);
+        err = lfs2_bd_prog(lfs2,
+                &lfs2->pcache, &lfs2->rcache, false,
+                commit->block, commit->off, &footer, sizeof(footer));
+        if (err) {
+            return err;
+        }
+
+        commit->off += sizeof(tag)+lfs2_tag_size(tag);
+        commit->ptag = tag ^ ((lfs2_tag_t)reset << 31);
+        commit->crc = LFS2_BLOCK_NULL; // reset crc for next "commit"
+    }
+
+    // flush buffers
+    int err = lfs2_bd_sync(lfs2, &lfs2->pcache, &lfs2->rcache, false);
+    if (err) {
+        return err;
+    }
+
+    // successful commit, check checksums to make sure
+    lfs2_off_t off = commit->begin;
+    lfs2_off_t noff = off1;
+    while (off < end) {
+        uint32_t crc = LFS2_BLOCK_NULL;
+        for (lfs2_off_t i = off; i < noff+sizeof(uint32_t); i++) {
+            // leave it up to caching to make this efficient
+            uint8_t dat;
+            err = lfs2_bd_read(lfs2,
+                    NULL, &lfs2->rcache, noff+sizeof(uint32_t)-i,
+                    commit->block, i, &dat, 1);
+            if (err) {
+                return err;
+            }
+
+            crc = lfs2_crc(crc, &dat, 1);
+        }
+
+        // detected write error?
+        if (crc != 0) {
+            return LFS2_ERR_CORRUPT;
+        }
+
+        // skip padding
+        off = lfs2_min(end - noff, 0x3fe) + noff;
+        if (off < end) {
+            off = lfs2_min(off, end - 2*sizeof(uint32_t));
+        }
+        noff = off + sizeof(uint32_t);
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_alloc(lfs2_t *lfs2, lfs2_mdir_t *dir) {
+    // allocate pair of dir blocks (backwards, so we write block 1 first)
+    for (int i = 0; i < 2; i++) {
+        int err = lfs2_alloc(lfs2, &dir->pair[(i+1)%2]);
+        if (err) {
+            return err;
+        }
+    }
+
+    // rather than clobbering one of the blocks we just pretend
+    // the revision may be valid
+    int err = lfs2_bd_read(lfs2,
+            NULL, &lfs2->rcache, sizeof(dir->rev),
+            dir->pair[0], 0, &dir->rev, sizeof(dir->rev));
+    dir->rev = lfs2_fromle32(dir->rev);
+    if (err && err != LFS2_ERR_CORRUPT) {
+        return err;
+    }
+
+    // make sure we don't immediately evict
+    dir->rev += dir->rev & 1;
+
+    // set defaults
+    dir->off = sizeof(dir->rev);
+    dir->etag = LFS2_BLOCK_NULL;
+    dir->count = 0;
+    dir->tail[0] = LFS2_BLOCK_NULL;
+    dir->tail[1] = LFS2_BLOCK_NULL;
+    dir->erased = false;
+    dir->split = false;
+
+    // don't write out yet, let caller take care of that
+    return 0;
+}
+
+static int lfs2_dir_drop(lfs2_t *lfs2, lfs2_mdir_t *dir, lfs2_mdir_t *tail) {
+    // steal state
+    int err = lfs2_dir_getgstate(lfs2, tail, &lfs2->gdelta);
+    if (err) {
+        return err;
+    }
+
+    // steal tail
+    lfs2_pair_tole32(tail->tail);
+    err = lfs2_dir_commit(lfs2, dir, LFS2_MKATTRS(
+            {LFS2_MKTAG(LFS2_TYPE_TAIL + tail->split, 0x3ff, 8), tail->tail}));
+    lfs2_pair_fromle32(tail->tail);
+    if (err) {
+        return err;
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_split(lfs2_t *lfs2,
+        lfs2_mdir_t *dir, const struct lfs2_mattr *attrs, int attrcount,
+        lfs2_mdir_t *source, uint16_t split, uint16_t end) {
+    // create tail directory
+    lfs2_mdir_t tail;
+    int err = lfs2_dir_alloc(lfs2, &tail);
+    if (err) {
+        return err;
+    }
+
+    tail.split = dir->split;
+    tail.tail[0] = dir->tail[0];
+    tail.tail[1] = dir->tail[1];
+
+    err = lfs2_dir_compact(lfs2, &tail, attrs, attrcount, source, split, end);
+    if (err) {
+        return err;
+    }
+
+    dir->tail[0] = tail.pair[0];
+    dir->tail[1] = tail.pair[1];
+    dir->split = true;
+
+    // update root if needed
+    if (lfs2_pair_cmp(dir->pair, lfs2->root) == 0 && split == 0) {
+        lfs2->root[0] = tail.pair[0];
+        lfs2->root[1] = tail.pair[1];
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_commit_size(void *p, lfs2_tag_t tag, const void *buffer) {
+    lfs2_size_t *size = p;
+    (void)buffer;
+
+    *size += lfs2_tag_dsize(tag);
+    return 0;
+}
+
+struct lfs2_dir_commit_commit {
+    lfs2_t *lfs2;
+    struct lfs2_commit *commit;
+};
+
+static int lfs2_dir_commit_commit(void *p, lfs2_tag_t tag, const void *buffer) {
+    struct lfs2_dir_commit_commit *commit = p;
+    return lfs2_dir_commitattr(commit->lfs2, commit->commit, tag, buffer);
+}
+
+static int lfs2_dir_compact(lfs2_t *lfs2,
+        lfs2_mdir_t *dir, const struct lfs2_mattr *attrs, int attrcount,
+        lfs2_mdir_t *source, uint16_t begin, uint16_t end) {
+    // save some state in case block is bad
+    const lfs2_block_t oldpair[2] = {dir->pair[1], dir->pair[0]};
+    bool relocated = false;
+    bool exhausted = false;
+
+    // should we split?
+    while (end - begin > 1) {
+        // find size
+        lfs2_size_t size = 0;
+        int err = lfs2_dir_traverse(lfs2,
+                source, 0, LFS2_BLOCK_NULL, attrs, attrcount, false,
+                LFS2_MKTAG(0x400, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_NAME, 0, 0),
+                begin, end, -begin,
+                lfs2_dir_commit_size, &size);
+        if (err) {
+            return err;
+        }
+
+        // space is complicated, we need room for tail, crc, gstate,
+        // cleanup delete, and we cap at half a block to give room
+        // for metadata updates.
+        if (end - begin < 0xff &&
+                size <= lfs2_min(lfs2->cfg->block_size - 36,
+                    lfs2_alignup(lfs2->cfg->block_size/2,
+                        lfs2->cfg->prog_size))) {
+            break;
+        }
+
+        // can't fit, need to split, we should really be finding the
+        // largest size that fits with a small binary search, but right now
+        // it's not worth the code size
+        uint16_t split = (end - begin) / 2;
+        err = lfs2_dir_split(lfs2, dir, attrs, attrcount,
+                source, begin+split, end);
+        if (err) {
+            // if we fail to split, we may be able to overcompact, unless
+            // we're too big for even the full block, in which case our
+            // only option is to error
+            if (err == LFS2_ERR_NOSPC && size <= lfs2->cfg->block_size - 36) {
+                break;
+            }
+            return err;
+        }
+
+        end = begin + split;
+    }
+
+    // increment revision count
+    dir->rev += 1;
+    if (lfs2->cfg->block_cycles > 0 &&
+            (dir->rev % (lfs2->cfg->block_cycles+1) == 0)) {
+        if (lfs2_pair_cmp(dir->pair, (const lfs2_block_t[2]){0, 1}) == 0) {
+            // oh no! we're writing too much to the superblock,
+            // should we expand?
+            lfs2_ssize_t res = lfs2_fs_size(lfs2);
+            if (res < 0) {
+                return res;
+            }
+
+            // do we have extra space? littlefs can't reclaim this space
+            // by itself, so expand cautiously
+            if ((lfs2_size_t)res < lfs2->cfg->block_count/2) {
+                LFS2_DEBUG("Expanding superblock at rev %"PRIu32, dir->rev);
+                int err = lfs2_dir_split(lfs2, dir, attrs, attrcount,
+                        source, begin, end);
+                if (err && err != LFS2_ERR_NOSPC) {
+                    return err;
+                }
+
+                // welp, we tried, if we ran out of space there's not much
+                // we can do, we'll error later if we've become frozen
+                if (!err) {
+                    end = begin;
+                }
+            }
+#ifdef LFS2_MIGRATE
+        } else if (lfs2_pair_cmp(dir->pair, lfs2->root) == 0 && lfs2->lfs21) {
+            // we can't relocate our root during migrations, as this would
+            // cause the superblock to get updated, which would clobber v1
+#endif
+        } else {
+            // we're writing too much, time to relocate
+            exhausted = true;
+            goto relocate;
+        }
+    }
+
+    // begin loop to commit compaction to blocks until a compact sticks
+    while (true) {
+        {
+            // There's nothing special about our global delta, so feed it into
+            // our local global delta
+            int err = lfs2_dir_getgstate(lfs2, dir, &lfs2->gdelta);
+            if (err) {
+                return err;
+            }
+
+            // setup commit state
+            struct lfs2_commit commit = {
+                .block = dir->pair[1],
+                .off = 0,
+                .ptag = LFS2_BLOCK_NULL,
+                .crc = LFS2_BLOCK_NULL,
+
+                .begin = 0,
+                .end = lfs2->cfg->block_size - 8,
+            };
+
+            // erase block to write to
+            err = lfs2_bd_erase(lfs2, dir->pair[1]);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+
+            // write out header
+            dir->rev = lfs2_tole32(dir->rev);
+            err = lfs2_dir_commitprog(lfs2, &commit,
+                    &dir->rev, sizeof(dir->rev));
+            dir->rev = lfs2_fromle32(dir->rev);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+
+            // traverse the directory, this time writing out all unique tags
+            err = lfs2_dir_traverse(lfs2,
+                    source, 0, LFS2_BLOCK_NULL, attrs, attrcount, false,
+                    LFS2_MKTAG(0x400, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_NAME, 0, 0),
+                    begin, end, -begin,
+                    lfs2_dir_commit_commit, &(struct lfs2_dir_commit_commit){
+                        lfs2, &commit});
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+
+            // commit tail, which may be new after last size check
+            if (!lfs2_pair_isnull(dir->tail)) {
+                lfs2_pair_tole32(dir->tail);
+                err = lfs2_dir_commitattr(lfs2, &commit,
+                        LFS2_MKTAG(LFS2_TYPE_TAIL + dir->split, 0x3ff, 8),
+                        dir->tail);
+                lfs2_pair_fromle32(dir->tail);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        goto relocate;
+                    }
+                    return err;
+                }
+            }
+
+            if (!relocated && !lfs2_gstate_iszero(&lfs2->gdelta)) {
+                // commit any globals, unless we're relocating,
+                // in which case our parent will steal our globals
+                lfs2_gstate_tole32(&lfs2->gdelta);
+                err = lfs2_dir_commitattr(lfs2, &commit,
+                        LFS2_MKTAG(LFS2_TYPE_MOVESTATE, 0x3ff,
+                            sizeof(lfs2->gdelta)), &lfs2->gdelta);
+                lfs2_gstate_fromle32(&lfs2->gdelta);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        goto relocate;
+                    }
+                    return err;
+                }
+            }
+
+            err = lfs2_dir_commitcrc(lfs2, &commit);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+
+            // successful compaction, swap dir pair to indicate most recent
+            LFS2_ASSERT(commit.off % lfs2->cfg->prog_size == 0);
+            lfs2_pair_swap(dir->pair);
+            dir->count = end - begin;
+            dir->off = commit.off;
+            dir->etag = commit.ptag;
+            // note we able to have already handled move here
+            if (lfs2_gstate_hasmovehere(&lfs2->gpending, dir->pair)) {
+                lfs2_gstate_xormove(&lfs2->gpending,
+                    &lfs2->gpending, 0x3ff, NULL);
+            }
+        }
+        break;
+
+relocate:
+        // commit was corrupted, drop caches and prepare to relocate block
+        relocated = true;
+        lfs2_cache_drop(lfs2, &lfs2->pcache);
+        if (!exhausted) {
+            LFS2_DEBUG("Bad block at %"PRIx32, dir->pair[1]);
+        }
+
+        // can't relocate superblock, filesystem is now frozen
+        if (lfs2_pair_cmp(oldpair, (const lfs2_block_t[2]){0, 1}) == 0) {
+            LFS2_WARN("Superblock %"PRIx32" has become unwritable", oldpair[1]);
+            return LFS2_ERR_NOSPC;
+        }
+
+        // relocate half of pair
+        int err = lfs2_alloc(lfs2, &dir->pair[1]);
+        if (err && (err != LFS2_ERR_NOSPC && !exhausted)) {
+            return err;
+        }
+
+        continue;
+    }
+
+    if (!relocated) {
+        lfs2->gstate = lfs2->gpending;
+        lfs2->gdelta = (struct lfs2_gstate){0};
+    } else {
+        // update references if we relocated
+        LFS2_DEBUG("Relocating %"PRIx32" %"PRIx32" -> %"PRIx32" %"PRIx32,
+                oldpair[0], oldpair[1], dir->pair[0], dir->pair[1]);
+        int err = lfs2_fs_relocate(lfs2, oldpair, dir->pair);
+        if (err) {
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+static int lfs2_dir_commit(lfs2_t *lfs2, lfs2_mdir_t *dir,
+        const struct lfs2_mattr *attrs, int attrcount) {
+    // check for any inline files that aren't RAM backed and
+    // forcefully evict them, needed for filesystem consistency
+    for (lfs2_file_t *f = (lfs2_file_t*)lfs2->mlist; f; f = f->next) {
+        if (dir != &f->m && lfs2_pair_cmp(f->m.pair, dir->pair) == 0 &&
+                f->type == LFS2_TYPE_REG && (f->flags & LFS2_F_INLINE) &&
+                f->ctz.size > lfs2->cfg->cache_size) {
+            int err = lfs2_file_outline(lfs2, f);
+            if (err) {
+                return err;
+            }
+
+            err = lfs2_file_flush(lfs2, f);
+            if (err) {
+                return err;
+            }
+        }
+    }
+
+    // calculate changes to the directory
+    lfs2_tag_t deletetag = LFS2_BLOCK_NULL;
+    lfs2_tag_t createtag = LFS2_BLOCK_NULL;
+    for (int i = 0; i < attrcount; i++) {
+        if (lfs2_tag_type3(attrs[i].tag) == LFS2_TYPE_CREATE) {
+            createtag = attrs[i].tag;
+            dir->count += 1;
+        } else if (lfs2_tag_type3(attrs[i].tag) == LFS2_TYPE_DELETE) {
+            deletetag = attrs[i].tag;
+            LFS2_ASSERT(dir->count > 0);
+            dir->count -= 1;
+        } else if (lfs2_tag_type1(attrs[i].tag) == LFS2_TYPE_TAIL) {
+            dir->tail[0] = ((lfs2_block_t*)attrs[i].buffer)[0];
+            dir->tail[1] = ((lfs2_block_t*)attrs[i].buffer)[1];
+            dir->split = (lfs2_tag_chunk(attrs[i].tag) & 1);
+            lfs2_pair_fromle32(dir->tail);
+        }
+    }
+
+    // do we have a pending move?
+    if (lfs2_gstate_hasmovehere(&lfs2->gpending, dir->pair)) {
+        deletetag = lfs2->gpending.tag & LFS2_MKTAG(0x7ff, 0x3ff, 0);
+        LFS2_ASSERT(dir->count > 0);
+        dir->count -= 1;
+
+        // mark gdelta so we reflect the move we will fix
+        lfs2_gstate_xormove(&lfs2->gdelta, &lfs2->gpending, 0x3ff, NULL);
+    }
+
+    // should we actually drop the directory block?
+    if (lfs2_tag_isvalid(deletetag) && dir->count == 0) {
+        lfs2_mdir_t pdir;
+        int err = lfs2_fs_pred(lfs2, dir->pair, &pdir);
+        if (err && err != LFS2_ERR_NOENT) {
+            return err;
+        }
+
+        if (err != LFS2_ERR_NOENT && pdir.split) {
+            return lfs2_dir_drop(lfs2, &pdir, dir);
+        }
+    }
+
+    if (dir->erased || dir->count >= 0xff) {
+        // try to commit
+        struct lfs2_commit commit = {
+            .block = dir->pair[0],
+            .off = dir->off,
+            .ptag = dir->etag,
+            .crc = LFS2_BLOCK_NULL,
+
+            .begin = dir->off,
+            .end = lfs2->cfg->block_size - 8,
+        };
+
+        // traverse attrs that need to be written out
+        lfs2_pair_tole32(dir->tail);
+        int err = lfs2_dir_traverse(lfs2,
+                dir, dir->off, dir->etag, attrs, attrcount, false,
+                0, 0, 0, 0, 0,
+                lfs2_dir_commit_commit, &(struct lfs2_dir_commit_commit){
+                    lfs2, &commit});
+        lfs2_pair_fromle32(dir->tail);
+        if (err) {
+            if (err == LFS2_ERR_NOSPC || err == LFS2_ERR_CORRUPT) {
+                goto compact;
+            }
+            return err;
+        }
+
+        // commit any global diffs if we have any
+        if (!lfs2_gstate_iszero(&lfs2->gdelta)) {
+            err = lfs2_dir_getgstate(lfs2, dir, &lfs2->gdelta);
+            if (err) {
+                return err;
+            }
+
+            lfs2_gstate_tole32(&lfs2->gdelta);
+            err = lfs2_dir_commitattr(lfs2, &commit,
+                    LFS2_MKTAG(LFS2_TYPE_MOVESTATE, 0x3ff,
+                        sizeof(lfs2->gdelta)), &lfs2->gdelta);
+            lfs2_gstate_fromle32(&lfs2->gdelta);
+            if (err) {
+                if (err == LFS2_ERR_NOSPC || err == LFS2_ERR_CORRUPT) {
+                    goto compact;
+                }
+                return err;
+            }
+        }
+
+        // finalize commit with the crc
+        err = lfs2_dir_commitcrc(lfs2, &commit);
+        if (err) {
+            if (err == LFS2_ERR_NOSPC || err == LFS2_ERR_CORRUPT) {
+                goto compact;
+            }
+            return err;
+        }
+
+        // successful commit, update dir
+        LFS2_ASSERT(commit.off % lfs2->cfg->prog_size == 0);
+        dir->off = commit.off;
+        dir->etag = commit.ptag;
+
+        // note we able to have already handled move here
+        if (lfs2_gstate_hasmovehere(&lfs2->gpending, dir->pair)) {
+            lfs2_gstate_xormove(&lfs2->gpending, &lfs2->gpending, 0x3ff, NULL);
+        }
+
+        // update gstate
+        lfs2->gstate = lfs2->gpending;
+        lfs2->gdelta = (struct lfs2_gstate){0};
+    } else {
+compact:
+        // fall back to compaction
+        lfs2_cache_drop(lfs2, &lfs2->pcache);
+
+        int err = lfs2_dir_compact(lfs2, dir, attrs, attrcount,
+                dir, 0, dir->count);
+        if (err) {
+            return err;
+        }
+    }
+
+    // update any directories that are affected
+    lfs2_mdir_t copy = *dir;
+
+    // two passes, once for things that aren't us, and one
+    // for things that are
+    for (struct lfs2_mlist *d = lfs2->mlist; d; d = d->next) {
+        if (lfs2_pair_cmp(d->m.pair, copy.pair) == 0) {
+            d->m = *dir;
+            if (d->id == lfs2_tag_id(deletetag)) {
+                d->m.pair[0] = LFS2_BLOCK_NULL;
+                d->m.pair[1] = LFS2_BLOCK_NULL;
+            } else if (d->id > lfs2_tag_id(deletetag)) {
+                d->id -= 1;
+                if (d->type == LFS2_TYPE_DIR) {
+                    ((lfs2_dir_t*)d)->pos -= 1;
+                }
+            } else if (&d->m != dir && d->id >= lfs2_tag_id(createtag)) {
+                d->id += 1;
+                if (d->type == LFS2_TYPE_DIR) {
+                    ((lfs2_dir_t*)d)->pos += 1;
+                }
+            }
+
+            while (d->id >= d->m.count && d->m.split) {
+                // we split and id is on tail now
+                d->id -= d->m.count;
+                int err = lfs2_dir_fetch(lfs2, &d->m, d->m.tail);
+                if (err) {
+                    return err;
+                }
+            }
+        }
+    }
+
+    return 0;
+}
+
+
+/// Top level directory operations ///
+int lfs2_mkdir(lfs2_t *lfs2, const char *path) {
+    LFS2_TRACE("lfs2_mkdir(%p, \"%s\")", (void*)lfs2, path);
+    // deorphan if we haven't yet, needed at most once after poweron
+    int err = lfs2_fs_forceconsistency(lfs2);
+    if (err) {
+        LFS2_TRACE("lfs2_mkdir -> %d", err);
+        return err;
+    }
+
+    lfs2_mdir_t cwd;
+    uint16_t id;
+    err = lfs2_dir_find(lfs2, &cwd, &path, &id);
+    if (!(err == LFS2_ERR_NOENT && id != 0x3ff)) {
+        LFS2_TRACE("lfs2_mkdir -> %d", (err < 0) ? err : LFS2_ERR_EXIST);
+        return (err < 0) ? err : LFS2_ERR_EXIST;
+    }
+
+    // check that name fits
+    lfs2_size_t nlen = strlen(path);
+    if (nlen > lfs2->name_max) {
+        LFS2_TRACE("lfs2_mkdir -> %d", LFS2_ERR_NAMETOOLONG);
+        return LFS2_ERR_NAMETOOLONG;
+    }
+
+    // build up new directory
+    lfs2_alloc_ack(lfs2);
+    lfs2_mdir_t dir;
+    err = lfs2_dir_alloc(lfs2, &dir);
+    if (err) {
+        LFS2_TRACE("lfs2_mkdir -> %d", err);
+        return err;
+    }
+
+    // find end of list
+    lfs2_mdir_t pred = cwd;
+    while (pred.split) {
+        err = lfs2_dir_fetch(lfs2, &pred, pred.tail);
+        if (err) {
+            LFS2_TRACE("lfs2_mkdir -> %d", err);
+            return err;
+        }
+    }
+
+    // setup dir
+    lfs2_pair_tole32(pred.tail);
+    err = lfs2_dir_commit(lfs2, &dir, LFS2_MKATTRS(
+            {LFS2_MKTAG(LFS2_TYPE_SOFTTAIL, 0x3ff, 8), pred.tail}));
+    lfs2_pair_fromle32(pred.tail);
+    if (err) {
+        LFS2_TRACE("lfs2_mkdir -> %d", err);
+        return err;
+    }
+
+    // current block end of list?
+    if (cwd.split) {
+        // update tails, this creates a desync
+        lfs2_fs_preporphans(lfs2, +1);
+        lfs2_pair_tole32(dir.pair);
+        err = lfs2_dir_commit(lfs2, &pred, LFS2_MKATTRS(
+                {LFS2_MKTAG(LFS2_TYPE_SOFTTAIL, 0x3ff, 8), dir.pair}));
+        lfs2_pair_fromle32(dir.pair);
+        if (err) {
+            LFS2_TRACE("lfs2_mkdir -> %d", err);
+            return err;
+        }
+        lfs2_fs_preporphans(lfs2, -1);
+    }
+
+    // now insert into our parent block
+    lfs2_pair_tole32(dir.pair);
+    err = lfs2_dir_commit(lfs2, &cwd, LFS2_MKATTRS(
+            {LFS2_MKTAG(LFS2_TYPE_CREATE, id, 0), NULL},
+            {LFS2_MKTAG(LFS2_TYPE_DIR, id, nlen), path},
+            {LFS2_MKTAG(LFS2_TYPE_DIRSTRUCT, id, 8), dir.pair},
+            {!cwd.split
+                ? LFS2_MKTAG(LFS2_TYPE_SOFTTAIL, 0x3ff, 8)
+                : LFS2_MKTAG(LFS2_FROM_NOOP, 0, 0), dir.pair}));
+    lfs2_pair_fromle32(dir.pair);
+    if (err) {
+        LFS2_TRACE("lfs2_mkdir -> %d", err);
+        return err;
+    }
+
+    LFS2_TRACE("lfs2_mkdir -> %d", 0);
+    return 0;
+}
+
+int lfs2_dir_open(lfs2_t *lfs2, lfs2_dir_t *dir, const char *path) {
+    LFS2_TRACE("lfs2_dir_open(%p, %p, \"%s\")", (void*)lfs2, (void*)dir, path);
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &dir->m, &path, NULL);
+    if (tag < 0) {
+        LFS2_TRACE("lfs2_dir_open -> %d", tag);
+        return tag;
+    }
+
+    if (lfs2_tag_type3(tag) != LFS2_TYPE_DIR) {
+        LFS2_TRACE("lfs2_dir_open -> %d", LFS2_ERR_NOTDIR);
+        return LFS2_ERR_NOTDIR;
+    }
+
+    lfs2_block_t pair[2];
+    if (lfs2_tag_id(tag) == 0x3ff) {
+        // handle root dir separately
+        pair[0] = lfs2->root[0];
+        pair[1] = lfs2->root[1];
+    } else {
+        // get dir pair from parent
+        lfs2_stag_t res = lfs2_dir_get(lfs2, &dir->m, LFS2_MKTAG(0x700, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_STRUCT, lfs2_tag_id(tag), 8), pair);
+        if (res < 0) {
+            LFS2_TRACE("lfs2_dir_open -> %d", res);
+            return res;
+        }
+        lfs2_pair_fromle32(pair);
+    }
+
+    // fetch first pair
+    int err = lfs2_dir_fetch(lfs2, &dir->m, pair);
+    if (err) {
+        LFS2_TRACE("lfs2_dir_open -> %d", err);
+        return err;
+    }
+
+    // setup entry
+    dir->head[0] = dir->m.pair[0];
+    dir->head[1] = dir->m.pair[1];
+    dir->id = 0;
+    dir->pos = 0;
+
+    // add to list of mdirs
+    dir->type = LFS2_TYPE_DIR;
+    dir->next = (lfs2_dir_t*)lfs2->mlist;
+    lfs2->mlist = (struct lfs2_mlist*)dir;
+
+    LFS2_TRACE("lfs2_dir_open -> %d", 0);
+    return 0;
+}
+
+int lfs2_dir_close(lfs2_t *lfs2, lfs2_dir_t *dir) {
+    LFS2_TRACE("lfs2_dir_close(%p, %p)", (void*)lfs2, (void*)dir);
+    // remove from list of mdirs
+    for (struct lfs2_mlist **p = &lfs2->mlist; *p; p = &(*p)->next) {
+        if (*p == (struct lfs2_mlist*)dir) {
+            *p = (*p)->next;
+            break;
+        }
+    }
+
+    LFS2_TRACE("lfs2_dir_close -> %d", 0);
+    return 0;
+}
+
+int lfs2_dir_read(lfs2_t *lfs2, lfs2_dir_t *dir, struct lfs2_info *info) {
+    LFS2_TRACE("lfs2_dir_read(%p, %p, %p)",
+            (void*)lfs2, (void*)dir, (void*)info);
+    memset(info, 0, sizeof(*info));
+
+    // special offset for '.' and '..'
+    if (dir->pos == 0) {
+        info->type = LFS2_TYPE_DIR;
+        strcpy(info->name, ".");
+        dir->pos += 1;
+        LFS2_TRACE("lfs2_dir_read -> %d", true);
+        return true;
+    } else if (dir->pos == 1) {
+        info->type = LFS2_TYPE_DIR;
+        strcpy(info->name, "..");
+        dir->pos += 1;
+        LFS2_TRACE("lfs2_dir_read -> %d", true);
+        return true;
+    }
+
+    while (true) {
+        if (dir->id == dir->m.count) {
+            if (!dir->m.split) {
+                LFS2_TRACE("lfs2_dir_read -> %d", false);
+                return false;
+            }
+
+            int err = lfs2_dir_fetch(lfs2, &dir->m, dir->m.tail);
+            if (err) {
+                LFS2_TRACE("lfs2_dir_read -> %d", err);
+                return err;
+            }
+
+            dir->id = 0;
+        }
+
+        int err = lfs2_dir_getinfo(lfs2, &dir->m, dir->id, info);
+        if (err && err != LFS2_ERR_NOENT) {
+            LFS2_TRACE("lfs2_dir_read -> %d", err);
+            return err;
+        }
+
+        dir->id += 1;
+        if (err != LFS2_ERR_NOENT) {
+            break;
+        }
+    }
+
+    dir->pos += 1;
+    LFS2_TRACE("lfs2_dir_read -> %d", true);
+    return true;
+}
+
+int lfs2_dir_seek(lfs2_t *lfs2, lfs2_dir_t *dir, lfs2_off_t off) {
+    LFS2_TRACE("lfs2_dir_seek(%p, %p, %"PRIu32")",
+            (void*)lfs2, (void*)dir, off);
+    // simply walk from head dir
+    int err = lfs2_dir_rewind(lfs2, dir);
+    if (err) {
+        LFS2_TRACE("lfs2_dir_seek -> %d", err);
+        return err;
+    }
+
+    // first two for ./..
+    dir->pos = lfs2_min(2, off);
+    off -= dir->pos;
+
+    while (off != 0) {
+        dir->id = lfs2_min(dir->m.count, off);
+        dir->pos += dir->id;
+        off -= dir->id;
+
+        if (dir->id == dir->m.count) {
+            if (!dir->m.split) {
+                LFS2_TRACE("lfs2_dir_seek -> %d", LFS2_ERR_INVAL);
+                return LFS2_ERR_INVAL;
+            }
+
+            err = lfs2_dir_fetch(lfs2, &dir->m, dir->m.tail);
+            if (err) {
+                LFS2_TRACE("lfs2_dir_seek -> %d", err);
+                return err;
+            }
+        }
+    }
+
+    LFS2_TRACE("lfs2_dir_seek -> %d", 0);
+    return 0;
+}
+
+lfs2_soff_t lfs2_dir_tell(lfs2_t *lfs2, lfs2_dir_t *dir) {
+    LFS2_TRACE("lfs2_dir_tell(%p, %p)", (void*)lfs2, (void*)dir);
+    (void)lfs2;
+    LFS2_TRACE("lfs2_dir_tell -> %"PRId32, dir->pos);
+    return dir->pos;
+}
+
+int lfs2_dir_rewind(lfs2_t *lfs2, lfs2_dir_t *dir) {
+    LFS2_TRACE("lfs2_dir_rewind(%p, %p)", (void*)lfs2, (void*)dir);
+    // reload the head dir
+    int err = lfs2_dir_fetch(lfs2, &dir->m, dir->head);
+    if (err) {
+        LFS2_TRACE("lfs2_dir_rewind -> %d", err);
+        return err;
+    }
+
+    dir->m.pair[0] = dir->head[0];
+    dir->m.pair[1] = dir->head[1];
+    dir->id = 0;
+    dir->pos = 0;
+    LFS2_TRACE("lfs2_dir_rewind -> %d", 0);
+    return 0;
+}
+
+
+/// File index list operations ///
+static int lfs2_ctz_index(lfs2_t *lfs2, lfs2_off_t *off) {
+    lfs2_off_t size = *off;
+    lfs2_off_t b = lfs2->cfg->block_size - 2*4;
+    lfs2_off_t i = size / b;
+    if (i == 0) {
+        return 0;
+    }
+
+    i = (size - 4*(lfs2_popc(i-1)+2)) / b;
+    *off = size - b*i - 4*lfs2_popc(i);
+    return i;
+}
+
+static int lfs2_ctz_find(lfs2_t *lfs2,
+        const lfs2_cache_t *pcache, lfs2_cache_t *rcache,
+        lfs2_block_t head, lfs2_size_t size,
+        lfs2_size_t pos, lfs2_block_t *block, lfs2_off_t *off) {
+    if (size == 0) {
+        *block = LFS2_BLOCK_NULL;
+        *off = 0;
+        return 0;
+    }
+
+    lfs2_off_t current = lfs2_ctz_index(lfs2, &(lfs2_off_t){size-1});
+    lfs2_off_t target = lfs2_ctz_index(lfs2, &pos);
+
+    while (current > target) {
+        lfs2_size_t skip = lfs2_min(
+                lfs2_npw2(current-target+1) - 1,
+                lfs2_ctz(current));
+
+        int err = lfs2_bd_read(lfs2,
+                pcache, rcache, sizeof(head),
+                head, 4*skip, &head, sizeof(head));
+        head = lfs2_fromle32(head);
+        if (err) {
+            return err;
+        }
+
+        LFS2_ASSERT(head >= 2 && head <= lfs2->cfg->block_count);
+        current -= 1 << skip;
+    }
+
+    *block = head;
+    *off = pos;
+    return 0;
+}
+
+static int lfs2_ctz_extend(lfs2_t *lfs2,
+        lfs2_cache_t *pcache, lfs2_cache_t *rcache,
+        lfs2_block_t head, lfs2_size_t size,
+        lfs2_block_t *block, lfs2_off_t *off) {
+    while (true) {
+        // go ahead and grab a block
+        lfs2_block_t nblock;
+        int err = lfs2_alloc(lfs2, &nblock);
+        if (err) {
+            return err;
+        }
+        LFS2_ASSERT(nblock >= 2 && nblock <= lfs2->cfg->block_count);
+
+        {
+            err = lfs2_bd_erase(lfs2, nblock);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+
+            if (size == 0) {
+                *block = nblock;
+                *off = 0;
+                return 0;
+            }
+
+            size -= 1;
+            lfs2_off_t index = lfs2_ctz_index(lfs2, &size);
+            size += 1;
+
+            // just copy out the last block if it is incomplete
+            if (size != lfs2->cfg->block_size) {
+                for (lfs2_off_t i = 0; i < size; i++) {
+                    uint8_t data;
+                    err = lfs2_bd_read(lfs2,
+                            NULL, rcache, size-i,
+                            head, i, &data, 1);
+                    if (err) {
+                        return err;
+                    }
+
+                    err = lfs2_bd_prog(lfs2,
+                            pcache, rcache, true,
+                            nblock, i, &data, 1);
+                    if (err) {
+                        if (err == LFS2_ERR_CORRUPT) {
+                            goto relocate;
+                        }
+                        return err;
+                    }
+                }
+
+                *block = nblock;
+                *off = size;
+                return 0;
+            }
+
+            // append block
+            index += 1;
+            lfs2_size_t skips = lfs2_ctz(index) + 1;
+
+            for (lfs2_off_t i = 0; i < skips; i++) {
+                head = lfs2_tole32(head);
+                err = lfs2_bd_prog(lfs2, pcache, rcache, true,
+                        nblock, 4*i, &head, 4);
+                head = lfs2_fromle32(head);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        goto relocate;
+                    }
+                    return err;
+                }
+
+                if (i != skips-1) {
+                    err = lfs2_bd_read(lfs2,
+                            NULL, rcache, sizeof(head),
+                            head, 4*i, &head, sizeof(head));
+                    head = lfs2_fromle32(head);
+                    if (err) {
+                        return err;
+                    }
+                }
+
+                LFS2_ASSERT(head >= 2 && head <= lfs2->cfg->block_count);
+            }
+
+            *block = nblock;
+            *off = 4*skips;
+            return 0;
+        }
+
+relocate:
+        LFS2_DEBUG("Bad block at %"PRIx32, nblock);
+
+        // just clear cache and try a new block
+        lfs2_cache_drop(lfs2, pcache);
+    }
+}
+
+static int lfs2_ctz_traverse(lfs2_t *lfs2,
+        const lfs2_cache_t *pcache, lfs2_cache_t *rcache,
+        lfs2_block_t head, lfs2_size_t size,
+        int (*cb)(void*, lfs2_block_t), void *data) {
+    if (size == 0) {
+        return 0;
+    }
+
+    lfs2_off_t index = lfs2_ctz_index(lfs2, &(lfs2_off_t){size-1});
+
+    while (true) {
+        int err = cb(data, head);
+        if (err) {
+            return err;
+        }
+
+        if (index == 0) {
+            return 0;
+        }
+
+        lfs2_block_t heads[2];
+        int count = 2 - (index & 1);
+        err = lfs2_bd_read(lfs2,
+                pcache, rcache, count*sizeof(head),
+                head, 0, &heads, count*sizeof(head));
+        heads[0] = lfs2_fromle32(heads[0]);
+        heads[1] = lfs2_fromle32(heads[1]);
+        if (err) {
+            return err;
+        }
+
+        for (int i = 0; i < count-1; i++) {
+            err = cb(data, heads[i]);
+            if (err) {
+                return err;
+            }
+        }
+
+        head = heads[count-1];
+        index -= count;
+    }
+}
+
+
+/// Top level file operations ///
+int lfs2_file_opencfg(lfs2_t *lfs2, lfs2_file_t *file,
+        const char *path, int flags,
+        const struct lfs2_file_config *cfg) {
+    LFS2_TRACE("lfs2_file_opencfg(%p, %p, \"%s\", %x, %p {"
+                 ".buffer=%p, .attrs=%p, .attr_count=%"PRIu32"})",
+            (void*)lfs2, (void*)file, path, flags,
+            (void*)cfg, cfg->buffer, (void*)cfg->attrs, cfg->attr_count);
+
+    // deorphan if we haven't yet, needed at most once after poweron
+    if ((flags & 3) != LFS2_O_RDONLY) {
+        int err = lfs2_fs_forceconsistency(lfs2);
+        if (err) {
+            LFS2_TRACE("lfs2_file_opencfg -> %d", err);
+            return err;
+        }
+    }
+
+    // setup simple file details
+    int err;
+    file->cfg = cfg;
+    file->flags = flags | LFS2_F_OPENED;
+    file->pos = 0;
+    file->off = 0;
+    file->cache.buffer = NULL;
+
+    // allocate entry for file if it doesn't exist
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &file->m, &path, &file->id);
+    if (tag < 0 && !(tag == LFS2_ERR_NOENT && file->id != 0x3ff)) {
+        err = tag;
+        goto cleanup;
+    }
+
+    // get id, add to list of mdirs to catch update changes
+    file->type = LFS2_TYPE_REG;
+    file->next = (lfs2_file_t*)lfs2->mlist;
+    lfs2->mlist = (struct lfs2_mlist*)file;
+
+    if (tag == LFS2_ERR_NOENT) {
+        if (!(flags & LFS2_O_CREAT)) {
+            err = LFS2_ERR_NOENT;
+            goto cleanup;
+        }
+
+        // check that name fits
+        lfs2_size_t nlen = strlen(path);
+        if (nlen > lfs2->name_max) {
+            err = LFS2_ERR_NAMETOOLONG;
+            goto cleanup;
+        }
+
+        // get next slot and create entry to remember name
+        err = lfs2_dir_commit(lfs2, &file->m, LFS2_MKATTRS(
+                {LFS2_MKTAG(LFS2_TYPE_CREATE, file->id, 0), NULL},
+                {LFS2_MKTAG(LFS2_TYPE_REG, file->id, nlen), path},
+                {LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, file->id, 0), NULL}));
+        if (err) {
+            err = LFS2_ERR_NAMETOOLONG;
+            goto cleanup;
+        }
+
+        tag = LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, 0, 0);
+    } else if (flags & LFS2_O_EXCL) {
+        err = LFS2_ERR_EXIST;
+        goto cleanup;
+    } else if (lfs2_tag_type3(tag) != LFS2_TYPE_REG) {
+        err = LFS2_ERR_ISDIR;
+        goto cleanup;
+    } else if (flags & LFS2_O_TRUNC) {
+        // truncate if requested
+        tag = LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, file->id, 0);
+        file->flags |= LFS2_F_DIRTY;
+    } else {
+        // try to load what's on disk, if it's inlined we'll fix it later
+        tag = lfs2_dir_get(lfs2, &file->m, LFS2_MKTAG(0x700, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_STRUCT, file->id, 8), &file->ctz);
+        if (tag < 0) {
+            err = tag;
+            goto cleanup;
+        }
+        lfs2_ctz_fromle32(&file->ctz);
+    }
+
+    // fetch attrs
+    for (unsigned i = 0; i < file->cfg->attr_count; i++) {
+        if ((file->flags & 3) != LFS2_O_WRONLY) {
+            lfs2_stag_t res = lfs2_dir_get(lfs2, &file->m,
+                    LFS2_MKTAG(0x7ff, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_USERATTR + file->cfg->attrs[i].type,
+                        file->id, file->cfg->attrs[i].size),
+                        file->cfg->attrs[i].buffer);
+            if (res < 0 && res != LFS2_ERR_NOENT) {
+                err = res;
+                goto cleanup;
+            }
+        }
+
+        if ((file->flags & 3) != LFS2_O_RDONLY) {
+            if (file->cfg->attrs[i].size > lfs2->attr_max) {
+                err = LFS2_ERR_NOSPC;
+                goto cleanup;
+            }
+
+            file->flags |= LFS2_F_DIRTY;
+        }
+    }
+
+    // allocate buffer if needed
+    if (file->cfg->buffer) {
+        file->cache.buffer = file->cfg->buffer;
+    } else {
+        file->cache.buffer = lfs2_malloc(lfs2->cfg->cache_size);
+        if (!file->cache.buffer) {
+            err = LFS2_ERR_NOMEM;
+            goto cleanup;
+        }
+    }
+
+    // zero to avoid information leak
+    lfs2_cache_zero(lfs2, &file->cache);
+
+    if (lfs2_tag_type3(tag) == LFS2_TYPE_INLINESTRUCT) {
+        // load inline files
+        file->ctz.head = LFS2_BLOCK_INLINE;
+        file->ctz.size = lfs2_tag_size(tag);
+        file->flags |= LFS2_F_INLINE;
+        file->cache.block = file->ctz.head;
+        file->cache.off = 0;
+        file->cache.size = lfs2->cfg->cache_size;
+
+        // don't always read (may be new/trunc file)
+        if (file->ctz.size > 0) {
+            lfs2_stag_t res = lfs2_dir_get(lfs2, &file->m,
+                    LFS2_MKTAG(0x700, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_STRUCT, file->id,
+                        lfs2_min(file->cache.size, 0x3fe)),
+                    file->cache.buffer);
+            if (res < 0) {
+                err = res;
+                goto cleanup;
+            }
+        }
+    }
+
+    LFS2_TRACE("lfs2_file_opencfg -> %d", 0);
+    return 0;
+
+cleanup:
+    // clean up lingering resources
+    file->flags |= LFS2_F_ERRED;
+    lfs2_file_close(lfs2, file);
+    LFS2_TRACE("lfs2_file_opencfg -> %d", err);
+    return err;
+}
+
+int lfs2_file_open(lfs2_t *lfs2, lfs2_file_t *file,
+        const char *path, int flags) {
+    LFS2_TRACE("lfs2_file_open(%p, %p, \"%s\", %x)",
+            (void*)lfs2, (void*)file, path, flags);
+    static const struct lfs2_file_config defaults = {0};
+    int err = lfs2_file_opencfg(lfs2, file, path, flags, &defaults);
+    LFS2_TRACE("lfs2_file_open -> %d", err);
+    return err;
+}
+
+int lfs2_file_close(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_TRACE("lfs2_file_close(%p, %p)", (void*)lfs2, (void*)file);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+
+    int err = lfs2_file_sync(lfs2, file);
+
+    // remove from list of mdirs
+    for (struct lfs2_mlist **p = &lfs2->mlist; *p; p = &(*p)->next) {
+        if (*p == (struct lfs2_mlist*)file) {
+            *p = (*p)->next;
+            break;
+        }
+    }
+
+    // clean up memory
+    if (!file->cfg->buffer) {
+        lfs2_free(file->cache.buffer);
+    }
+
+    file->flags &= ~LFS2_F_OPENED;
+    LFS2_TRACE("lfs2_file_close -> %d", err);
+    return err;
+}
+
+static int lfs2_file_relocate(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+
+    while (true) {
+        // just relocate what exists into new block
+        lfs2_block_t nblock;
+        int err = lfs2_alloc(lfs2, &nblock);
+        if (err) {
+            return err;
+        }
+
+        err = lfs2_bd_erase(lfs2, nblock);
+        if (err) {
+            if (err == LFS2_ERR_CORRUPT) {
+                goto relocate;
+            }
+            return err;
+        }
+
+        // either read from dirty cache or disk
+        for (lfs2_off_t i = 0; i < file->off; i++) {
+            uint8_t data;
+            if (file->flags & LFS2_F_INLINE) {
+                err = lfs2_dir_getread(lfs2, &file->m,
+                        // note we evict inline files before they can be dirty
+                        NULL, &file->cache, file->off-i,
+                        LFS2_MKTAG(0xfff, 0x1ff, 0),
+                        LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, file->id, 0),
+                        i, &data, 1);
+                if (err) {
+                    return err;
+                }
+            } else {
+                err = lfs2_bd_read(lfs2,
+                        &file->cache, &lfs2->rcache, file->off-i,
+                        file->block, i, &data, 1);
+                if (err) {
+                    return err;
+                }
+            }
+
+            err = lfs2_bd_prog(lfs2,
+                    &lfs2->pcache, &lfs2->rcache, true,
+                    nblock, i, &data, 1);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                return err;
+            }
+        }
+
+        // copy over new state of file
+        memcpy(file->cache.buffer, lfs2->pcache.buffer, lfs2->cfg->cache_size);
+        file->cache.block = lfs2->pcache.block;
+        file->cache.off = lfs2->pcache.off;
+        file->cache.size = lfs2->pcache.size;
+        lfs2_cache_zero(lfs2, &lfs2->pcache);
+
+        file->block = nblock;
+        file->flags |= LFS2_F_WRITING;
+        return 0;
+
+relocate:
+        LFS2_DEBUG("Bad block at %"PRIx32, nblock);
+
+        // just clear cache and try a new block
+        lfs2_cache_drop(lfs2, &lfs2->pcache);
+    }
+}
+
+static int lfs2_file_outline(lfs2_t *lfs2, lfs2_file_t *file) {
+    file->off = file->pos;
+    lfs2_alloc_ack(lfs2);
+    int err = lfs2_file_relocate(lfs2, file);
+    if (err) {
+        return err;
+    }
+
+    file->flags &= ~LFS2_F_INLINE;
+    return 0;
+}
+
+static int lfs2_file_flush(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+
+    if (file->flags & LFS2_F_READING) {
+        if (!(file->flags & LFS2_F_INLINE)) {
+            lfs2_cache_drop(lfs2, &file->cache);
+        }
+        file->flags &= ~LFS2_F_READING;
+    }
+
+    if (file->flags & LFS2_F_WRITING) {
+        lfs2_off_t pos = file->pos;
+
+        if (!(file->flags & LFS2_F_INLINE)) {
+            // copy over anything after current branch
+            lfs2_file_t orig = {
+                .ctz.head = file->ctz.head,
+                .ctz.size = file->ctz.size,
+                .flags = LFS2_O_RDONLY | LFS2_F_OPENED,
+                .pos = file->pos,
+                .cache = lfs2->rcache,
+            };
+            lfs2_cache_drop(lfs2, &lfs2->rcache);
+
+            while (file->pos < file->ctz.size) {
+                // copy over a byte at a time, leave it up to caching
+                // to make this efficient
+                uint8_t data;
+                lfs2_ssize_t res = lfs2_file_read(lfs2, &orig, &data, 1);
+                if (res < 0) {
+                    return res;
+                }
+
+                res = lfs2_file_write(lfs2, file, &data, 1);
+                if (res < 0) {
+                    return res;
+                }
+
+                // keep our reference to the rcache in sync
+                if (lfs2->rcache.block != LFS2_BLOCK_NULL) {
+                    lfs2_cache_drop(lfs2, &orig.cache);
+                    lfs2_cache_drop(lfs2, &lfs2->rcache);
+                }
+            }
+
+            // write out what we have
+            while (true) {
+                int err = lfs2_bd_flush(lfs2, &file->cache, &lfs2->rcache, true);
+                if (err) {
+                    if (err == LFS2_ERR_CORRUPT) {
+                        goto relocate;
+                    }
+                    return err;
+                }
+
+                break;
+
+relocate:
+                LFS2_DEBUG("Bad block at %"PRIx32, file->block);
+                err = lfs2_file_relocate(lfs2, file);
+                if (err) {
+                    return err;
+                }
+            }
+        } else {
+            file->pos = lfs2_max(file->pos, file->ctz.size);
+        }
+
+        // actual file updates
+        file->ctz.head = file->block;
+        file->ctz.size = file->pos;
+        file->flags &= ~LFS2_F_WRITING;
+        file->flags |= LFS2_F_DIRTY;
+
+        file->pos = pos;
+    }
+
+    return 0;
+}
+
+int lfs2_file_sync(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_TRACE("lfs2_file_sync(%p, %p)", (void*)lfs2, (void*)file);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+
+    while (true) {
+        int err = lfs2_file_flush(lfs2, file);
+        if (err) {
+            file->flags |= LFS2_F_ERRED;
+            LFS2_TRACE("lfs2_file_sync -> %d", err);
+            return err;
+        }
+
+        if ((file->flags & LFS2_F_DIRTY) &&
+                !(file->flags & LFS2_F_ERRED) &&
+                !lfs2_pair_isnull(file->m.pair)) {
+            // update dir entry
+            uint16_t type;
+            const void *buffer;
+            lfs2_size_t size;
+            struct lfs2_ctz ctz;
+            if (file->flags & LFS2_F_INLINE) {
+                // inline the whole file
+                type = LFS2_TYPE_INLINESTRUCT;
+                buffer = file->cache.buffer;
+                size = file->ctz.size;
+            } else {
+                // update the ctz reference
+                type = LFS2_TYPE_CTZSTRUCT;
+                // copy ctz so alloc will work during a relocate
+                ctz = file->ctz;
+                lfs2_ctz_tole32(&ctz);
+                buffer = &ctz;
+                size = sizeof(ctz);
+            }
+
+            // commit file data and attributes
+            err = lfs2_dir_commit(lfs2, &file->m, LFS2_MKATTRS(
+                    {LFS2_MKTAG(type, file->id, size), buffer},
+                    {LFS2_MKTAG(LFS2_FROM_USERATTRS, file->id,
+                        file->cfg->attr_count), file->cfg->attrs}));
+            if (err) {
+                if (err == LFS2_ERR_NOSPC && (file->flags & LFS2_F_INLINE)) {
+                    goto relocate;
+                }
+                file->flags |= LFS2_F_ERRED;
+                LFS2_TRACE("lfs2_file_sync -> %d", err);
+                return err;
+            }
+
+            file->flags &= ~LFS2_F_DIRTY;
+        }
+
+        LFS2_TRACE("lfs2_file_sync -> %d", 0);
+        return 0;
+
+relocate:
+        // inline file doesn't fit anymore
+        err = lfs2_file_outline(lfs2, file);
+        if (err) {
+            file->flags |= LFS2_F_ERRED;
+            LFS2_TRACE("lfs2_file_sync -> %d", err);
+            return err;
+        }
+    }
+}
+
+lfs2_ssize_t lfs2_file_read(lfs2_t *lfs2, lfs2_file_t *file,
+        void *buffer, lfs2_size_t size) {
+    LFS2_TRACE("lfs2_file_read(%p, %p, %p, %"PRIu32")",
+            (void*)lfs2, (void*)file, buffer, size);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+    LFS2_ASSERT((file->flags & 3) != LFS2_O_WRONLY);
+
+    uint8_t *data = buffer;
+    lfs2_size_t nsize = size;
+
+    if (file->flags & LFS2_F_WRITING) {
+        // flush out any writes
+        int err = lfs2_file_flush(lfs2, file);
+        if (err) {
+            LFS2_TRACE("lfs2_file_read -> %"PRId32, err);
+            return err;
+        }
+    }
+
+    if (file->pos >= file->ctz.size) {
+        // eof if past end
+        LFS2_TRACE("lfs2_file_read -> %"PRId32, 0);
+        return 0;
+    }
+
+    size = lfs2_min(size, file->ctz.size - file->pos);
+    nsize = size;
+
+    while (nsize > 0) {
+        // check if we need a new block
+        if (!(file->flags & LFS2_F_READING) ||
+                file->off == lfs2->cfg->block_size) {
+            if (!(file->flags & LFS2_F_INLINE)) {
+                int err = lfs2_ctz_find(lfs2, NULL, &file->cache,
+                        file->ctz.head, file->ctz.size,
+                        file->pos, &file->block, &file->off);
+                if (err) {
+                    LFS2_TRACE("lfs2_file_read -> %"PRId32, err);
+                    return err;
+                }
+            } else {
+                file->block = LFS2_BLOCK_INLINE;
+                file->off = file->pos;
+            }
+
+            file->flags |= LFS2_F_READING;
+        }
+
+        // read as much as we can in current block
+        lfs2_size_t diff = lfs2_min(nsize, lfs2->cfg->block_size - file->off);
+        if (file->flags & LFS2_F_INLINE) {
+            int err = lfs2_dir_getread(lfs2, &file->m,
+                    NULL, &file->cache, lfs2->cfg->block_size,
+                    LFS2_MKTAG(0xfff, 0x1ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, file->id, 0),
+                    file->off, data, diff);
+            if (err) {
+                LFS2_TRACE("lfs2_file_read -> %"PRId32, err);
+                return err;
+            }
+        } else {
+            int err = lfs2_bd_read(lfs2,
+                    NULL, &file->cache, lfs2->cfg->block_size,
+                    file->block, file->off, data, diff);
+            if (err) {
+                LFS2_TRACE("lfs2_file_read -> %"PRId32, err);
+                return err;
+            }
+        }
+
+        file->pos += diff;
+        file->off += diff;
+        data += diff;
+        nsize -= diff;
+    }
+
+    LFS2_TRACE("lfs2_file_read -> %"PRId32, size);
+    return size;
+}
+
+lfs2_ssize_t lfs2_file_write(lfs2_t *lfs2, lfs2_file_t *file,
+        const void *buffer, lfs2_size_t size) {
+    LFS2_TRACE("lfs2_file_write(%p, %p, %p, %"PRIu32")",
+            (void*)lfs2, (void*)file, buffer, size);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+    LFS2_ASSERT((file->flags & 3) != LFS2_O_RDONLY);
+
+    const uint8_t *data = buffer;
+    lfs2_size_t nsize = size;
+
+    if (file->flags & LFS2_F_READING) {
+        // drop any reads
+        int err = lfs2_file_flush(lfs2, file);
+        if (err) {
+            LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+            return err;
+        }
+    }
+
+    if ((file->flags & LFS2_O_APPEND) && file->pos < file->ctz.size) {
+        file->pos = file->ctz.size;
+    }
+
+    if (file->pos + size > lfs2->file_max) {
+        // Larger than file limit?
+        LFS2_TRACE("lfs2_file_write -> %"PRId32, LFS2_ERR_FBIG);
+        return LFS2_ERR_FBIG;
+    }
+
+    if (!(file->flags & LFS2_F_WRITING) && file->pos > file->ctz.size) {
+        // fill with zeros
+        lfs2_off_t pos = file->pos;
+        file->pos = file->ctz.size;
+
+        while (file->pos < pos) {
+            lfs2_ssize_t res = lfs2_file_write(lfs2, file, &(uint8_t){0}, 1);
+            if (res < 0) {
+                LFS2_TRACE("lfs2_file_write -> %"PRId32, res);
+                return res;
+            }
+        }
+    }
+
+    if ((file->flags & LFS2_F_INLINE) &&
+            lfs2_max(file->pos+nsize, file->ctz.size) >
+            lfs2_min(0x3fe, lfs2_min(
+                lfs2->cfg->cache_size, lfs2->cfg->block_size/8))) {
+        // inline file doesn't fit anymore
+        int err = lfs2_file_outline(lfs2, file);
+        if (err) {
+            file->flags |= LFS2_F_ERRED;
+            LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+            return err;
+        }
+    }
+
+    while (nsize > 0) {
+        // check if we need a new block
+        if (!(file->flags & LFS2_F_WRITING) ||
+                file->off == lfs2->cfg->block_size) {
+            if (!(file->flags & LFS2_F_INLINE)) {
+                if (!(file->flags & LFS2_F_WRITING) && file->pos > 0) {
+                    // find out which block we're extending from
+                    int err = lfs2_ctz_find(lfs2, NULL, &file->cache,
+                            file->ctz.head, file->ctz.size,
+                            file->pos-1, &file->block, &file->off);
+                    if (err) {
+                        file->flags |= LFS2_F_ERRED;
+                        LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+                        return err;
+                    }
+
+                    // mark cache as dirty since we may have read data into it
+                    lfs2_cache_zero(lfs2, &file->cache);
+                }
+
+                // extend file with new blocks
+                lfs2_alloc_ack(lfs2);
+                int err = lfs2_ctz_extend(lfs2, &file->cache, &lfs2->rcache,
+                        file->block, file->pos,
+                        &file->block, &file->off);
+                if (err) {
+                    file->flags |= LFS2_F_ERRED;
+                    LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+                    return err;
+                }
+            } else {
+                file->block = LFS2_BLOCK_INLINE;
+                file->off = file->pos;
+            }
+
+            file->flags |= LFS2_F_WRITING;
+        }
+
+        // program as much as we can in current block
+        lfs2_size_t diff = lfs2_min(nsize, lfs2->cfg->block_size - file->off);
+        while (true) {
+            int err = lfs2_bd_prog(lfs2, &file->cache, &lfs2->rcache, true,
+                    file->block, file->off, data, diff);
+            if (err) {
+                if (err == LFS2_ERR_CORRUPT) {
+                    goto relocate;
+                }
+                file->flags |= LFS2_F_ERRED;
+                LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+                return err;
+            }
+
+            break;
+relocate:
+            err = lfs2_file_relocate(lfs2, file);
+            if (err) {
+                file->flags |= LFS2_F_ERRED;
+                LFS2_TRACE("lfs2_file_write -> %"PRId32, err);
+                return err;
+            }
+        }
+
+        file->pos += diff;
+        file->off += diff;
+        data += diff;
+        nsize -= diff;
+
+        lfs2_alloc_ack(lfs2);
+    }
+
+    file->flags &= ~LFS2_F_ERRED;
+    LFS2_TRACE("lfs2_file_write -> %"PRId32, size);
+    return size;
+}
+
+lfs2_soff_t lfs2_file_seek(lfs2_t *lfs2, lfs2_file_t *file,
+        lfs2_soff_t off, int whence) {
+    LFS2_TRACE("lfs2_file_seek(%p, %p, %"PRId32", %d)",
+            (void*)lfs2, (void*)file, off, whence);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+
+    // write out everything beforehand, may be noop if rdonly
+    int err = lfs2_file_flush(lfs2, file);
+    if (err) {
+        LFS2_TRACE("lfs2_file_seek -> %"PRId32, err);
+        return err;
+    }
+
+    // find new pos
+    lfs2_off_t npos = file->pos;
+    if (whence == LFS2_SEEK_SET) {
+        npos = off;
+    } else if (whence == LFS2_SEEK_CUR) {
+        npos = file->pos + off;
+    } else if (whence == LFS2_SEEK_END) {
+        npos = file->ctz.size + off;
+    }
+
+    if (npos > lfs2->file_max) {
+        // file position out of range
+        LFS2_TRACE("lfs2_file_seek -> %"PRId32, LFS2_ERR_INVAL);
+        return LFS2_ERR_INVAL;
+    }
+
+    // update pos
+    file->pos = npos;
+    LFS2_TRACE("lfs2_file_seek -> %"PRId32, npos);
+    return npos;
+}
+
+int lfs2_file_truncate(lfs2_t *lfs2, lfs2_file_t *file, lfs2_off_t size) {
+    LFS2_TRACE("lfs2_file_truncate(%p, %p, %"PRIu32")",
+            (void*)lfs2, (void*)file, size);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+    LFS2_ASSERT((file->flags & 3) != LFS2_O_RDONLY);
+
+    if (size > LFS2_FILE_MAX) {
+        LFS2_TRACE("lfs2_file_truncate -> %d", LFS2_ERR_INVAL);
+        return LFS2_ERR_INVAL;
+    }
+
+    lfs2_off_t pos = file->pos;
+    lfs2_off_t oldsize = lfs2_file_size(lfs2, file);
+    if (size < oldsize) {
+        // need to flush since directly changing metadata
+        int err = lfs2_file_flush(lfs2, file);
+        if (err) {
+            LFS2_TRACE("lfs2_file_truncate -> %d", err);
+            return err;
+        }
+
+        // lookup new head in ctz skip list
+        err = lfs2_ctz_find(lfs2, NULL, &file->cache,
+                file->ctz.head, file->ctz.size,
+                size, &file->block, &file->off);
+        if (err) {
+            LFS2_TRACE("lfs2_file_truncate -> %d", err);
+            return err;
+        }
+
+        file->ctz.head = file->block;
+        file->ctz.size = size;
+        file->flags |= LFS2_F_DIRTY | LFS2_F_READING;
+    } else if (size > oldsize) {
+        // flush+seek if not already at end
+        if (file->pos != oldsize) {
+            lfs2_soff_t res = lfs2_file_seek(lfs2, file, 0, LFS2_SEEK_END);
+            if (res < 0) {
+                LFS2_TRACE("lfs2_file_truncate -> %d", res);
+                return (int)res;
+            }
+        }
+
+        // fill with zeros
+        while (file->pos < size) {
+            lfs2_ssize_t res = lfs2_file_write(lfs2, file, &(uint8_t){0}, 1);
+            if (res < 0) {
+                LFS2_TRACE("lfs2_file_truncate -> %d", res);
+                return (int)res;
+            }
+        }
+    }
+
+    // restore pos
+    lfs2_soff_t res = lfs2_file_seek(lfs2, file, pos, LFS2_SEEK_SET);
+    if (res < 0) {
+      LFS2_TRACE("lfs2_file_truncate -> %d", res);
+      return (int)res;
+    }
+
+    LFS2_TRACE("lfs2_file_truncate -> %d", 0);
+    return 0;
+}
+
+lfs2_soff_t lfs2_file_tell(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_TRACE("lfs2_file_tell(%p, %p)", (void*)lfs2, (void*)file);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+    (void)lfs2;
+    LFS2_TRACE("lfs2_file_tell -> %"PRId32, file->pos);
+    return file->pos;
+}
+
+int lfs2_file_rewind(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_TRACE("lfs2_file_rewind(%p, %p)", (void*)lfs2, (void*)file);
+    lfs2_soff_t res = lfs2_file_seek(lfs2, file, 0, LFS2_SEEK_SET);
+    if (res < 0) {
+        LFS2_TRACE("lfs2_file_rewind -> %d", res);
+        return (int)res;
+    }
+
+    LFS2_TRACE("lfs2_file_rewind -> %d", 0);
+    return 0;
+}
+
+lfs2_soff_t lfs2_file_size(lfs2_t *lfs2, lfs2_file_t *file) {
+    LFS2_TRACE("lfs2_file_size(%p, %p)", (void*)lfs2, (void*)file);
+    LFS2_ASSERT(file->flags & LFS2_F_OPENED);
+    (void)lfs2;
+    if (file->flags & LFS2_F_WRITING) {
+        LFS2_TRACE("lfs2_file_size -> %"PRId32,
+                lfs2_max(file->pos, file->ctz.size));
+        return lfs2_max(file->pos, file->ctz.size);
+    } else {
+        LFS2_TRACE("lfs2_file_size -> %"PRId32, file->ctz.size);
+        return file->ctz.size;
+    }
+}
+
+
+/// General fs operations ///
+int lfs2_stat(lfs2_t *lfs2, const char *path, struct lfs2_info *info) {
+    LFS2_TRACE("lfs2_stat(%p, \"%s\", %p)", (void*)lfs2, path, (void*)info);
+    lfs2_mdir_t cwd;
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &cwd, &path, NULL);
+    if (tag < 0) {
+        LFS2_TRACE("lfs2_stat -> %d", tag);
+        return (int)tag;
+    }
+
+    int err = lfs2_dir_getinfo(lfs2, &cwd, lfs2_tag_id(tag), info);
+    LFS2_TRACE("lfs2_stat -> %d", err);
+    return err;
+}
+
+int lfs2_remove(lfs2_t *lfs2, const char *path) {
+    LFS2_TRACE("lfs2_remove(%p, \"%s\")", (void*)lfs2, path);
+    // deorphan if we haven't yet, needed at most once after poweron
+    int err = lfs2_fs_forceconsistency(lfs2);
+    if (err) {
+        LFS2_TRACE("lfs2_remove -> %d", err);
+        return err;
+    }
+
+    lfs2_mdir_t cwd;
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &cwd, &path, NULL);
+    if (tag < 0 || lfs2_tag_id(tag) == 0x3ff) {
+        LFS2_TRACE("lfs2_remove -> %d", (tag < 0) ? tag : LFS2_ERR_INVAL);
+        return (tag < 0) ? (int)tag : LFS2_ERR_INVAL;
+    }
+
+    lfs2_mdir_t dir;
+    if (lfs2_tag_type3(tag) == LFS2_TYPE_DIR) {
+        // must be empty before removal
+        lfs2_block_t pair[2];
+        lfs2_stag_t res = lfs2_dir_get(lfs2, &cwd, LFS2_MKTAG(0x700, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_STRUCT, lfs2_tag_id(tag), 8), pair);
+        if (res < 0) {
+            LFS2_TRACE("lfs2_remove -> %d", res);
+            return (int)res;
+        }
+        lfs2_pair_fromle32(pair);
+
+        err = lfs2_dir_fetch(lfs2, &dir, pair);
+        if (err) {
+            LFS2_TRACE("lfs2_remove -> %d", err);
+            return err;
+        }
+
+        if (dir.count > 0 || dir.split) {
+            LFS2_TRACE("lfs2_remove -> %d", LFS2_ERR_NOTEMPTY);
+            return LFS2_ERR_NOTEMPTY;
+        }
+
+        // mark fs as orphaned
+        lfs2_fs_preporphans(lfs2, +1);
+    }
+
+    // delete the entry
+    err = lfs2_dir_commit(lfs2, &cwd, LFS2_MKATTRS(
+            {LFS2_MKTAG(LFS2_TYPE_DELETE, lfs2_tag_id(tag), 0), NULL}));
+    if (err) {
+        LFS2_TRACE("lfs2_remove -> %d", err);
+        return err;
+    }
+
+    if (lfs2_tag_type3(tag) == LFS2_TYPE_DIR) {
+        // fix orphan
+        lfs2_fs_preporphans(lfs2, -1);
+
+        err = lfs2_fs_pred(lfs2, dir.pair, &cwd);
+        if (err) {
+            LFS2_TRACE("lfs2_remove -> %d", err);
+            return err;
+        }
+
+        err = lfs2_dir_drop(lfs2, &cwd, &dir);
+        if (err) {
+            LFS2_TRACE("lfs2_remove -> %d", err);
+            return err;
+        }
+    }
+
+    LFS2_TRACE("lfs2_remove -> %d", 0);
+    return 0;
+}
+
+int lfs2_rename(lfs2_t *lfs2, const char *oldpath, const char *newpath) {
+    LFS2_TRACE("lfs2_rename(%p, \"%s\", \"%s\")", (void*)lfs2, oldpath, newpath);
+
+    // deorphan if we haven't yet, needed at most once after poweron
+    int err = lfs2_fs_forceconsistency(lfs2);
+    if (err) {
+        LFS2_TRACE("lfs2_rename -> %d", err);
+        return err;
+    }
+
+    // find old entry
+    lfs2_mdir_t oldcwd;
+    lfs2_stag_t oldtag = lfs2_dir_find(lfs2, &oldcwd, &oldpath, NULL);
+    if (oldtag < 0 || lfs2_tag_id(oldtag) == 0x3ff) {
+        LFS2_TRACE("lfs2_rename -> %d", (oldtag < 0) ? oldtag : LFS2_ERR_INVAL);
+        return (oldtag < 0) ? (int)oldtag : LFS2_ERR_INVAL;
+    }
+
+    // find new entry
+    lfs2_mdir_t newcwd;
+    uint16_t newid;
+    lfs2_stag_t prevtag = lfs2_dir_find(lfs2, &newcwd, &newpath, &newid);
+    if ((prevtag < 0 || lfs2_tag_id(prevtag) == 0x3ff) &&
+            !(prevtag == LFS2_ERR_NOENT && newid != 0x3ff)) {
+        LFS2_TRACE("lfs2_rename -> %d", (prevtag < 0) ? prevtag : LFS2_ERR_INVAL);
+        return (prevtag < 0) ? (int)prevtag : LFS2_ERR_INVAL;
+    }
+
+    lfs2_mdir_t prevdir;
+    if (prevtag == LFS2_ERR_NOENT) {
+        // check that name fits
+        lfs2_size_t nlen = strlen(newpath);
+        if (nlen > lfs2->name_max) {
+            LFS2_TRACE("lfs2_rename -> %d", LFS2_ERR_NAMETOOLONG);
+            return LFS2_ERR_NAMETOOLONG;
+        }
+    } else if (lfs2_tag_type3(prevtag) != lfs2_tag_type3(oldtag)) {
+        LFS2_TRACE("lfs2_rename -> %d", LFS2_ERR_ISDIR);
+        return LFS2_ERR_ISDIR;
+    } else if (lfs2_tag_type3(prevtag) == LFS2_TYPE_DIR) {
+        // must be empty before removal
+        lfs2_block_t prevpair[2];
+        lfs2_stag_t res = lfs2_dir_get(lfs2, &newcwd, LFS2_MKTAG(0x700, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_STRUCT, newid, 8), prevpair);
+        if (res < 0) {
+            LFS2_TRACE("lfs2_rename -> %d", res);
+            return (int)res;
+        }
+        lfs2_pair_fromle32(prevpair);
+
+        // must be empty before removal
+        err = lfs2_dir_fetch(lfs2, &prevdir, prevpair);
+        if (err) {
+            LFS2_TRACE("lfs2_rename -> %d", err);
+            return err;
+        }
+
+        if (prevdir.count > 0 || prevdir.split) {
+            LFS2_TRACE("lfs2_rename -> %d", LFS2_ERR_NOTEMPTY);
+            return LFS2_ERR_NOTEMPTY;
+        }
+
+        // mark fs as orphaned
+        lfs2_fs_preporphans(lfs2, +1);
+    }
+
+    // create move to fix later
+    uint16_t newoldtagid = lfs2_tag_id(oldtag);
+    if (lfs2_pair_cmp(oldcwd.pair, newcwd.pair) == 0 &&
+            prevtag == LFS2_ERR_NOENT && newid <= newoldtagid) {
+        // there is a small chance we are being renamed in the same directory
+        // to an id less than our old id, the global update to handle this
+        // is a bit messy
+        newoldtagid += 1;
+    }
+
+    lfs2_fs_prepmove(lfs2, newoldtagid, oldcwd.pair);
+
+    // move over all attributes
+    err = lfs2_dir_commit(lfs2, &newcwd, LFS2_MKATTRS(
+            {prevtag != LFS2_ERR_NOENT
+                ? LFS2_MKTAG(LFS2_TYPE_DELETE, newid, 0)
+                : LFS2_MKTAG(LFS2_FROM_NOOP, 0, 0), NULL},
+            {LFS2_MKTAG(LFS2_TYPE_CREATE, newid, 0), NULL},
+            {LFS2_MKTAG(lfs2_tag_type3(oldtag), newid, strlen(newpath)),
+                newpath},
+            {LFS2_MKTAG(LFS2_FROM_MOVE, newid, lfs2_tag_id(oldtag)), &oldcwd}));
+    if (err) {
+        LFS2_TRACE("lfs2_rename -> %d", err);
+        return err;
+    }
+
+    // let commit clean up after move (if we're different! otherwise move
+    // logic already fixed it for us)
+    if (lfs2_pair_cmp(oldcwd.pair, newcwd.pair) != 0) {
+        err = lfs2_dir_commit(lfs2, &oldcwd, NULL, 0);
+        if (err) {
+            LFS2_TRACE("lfs2_rename -> %d", err);
+            return err;
+        }
+    }
+
+    if (prevtag != LFS2_ERR_NOENT && lfs2_tag_type3(prevtag) == LFS2_TYPE_DIR) {
+        // fix orphan
+        lfs2_fs_preporphans(lfs2, -1);
+
+        err = lfs2_fs_pred(lfs2, prevdir.pair, &newcwd);
+        if (err) {
+            LFS2_TRACE("lfs2_rename -> %d", err);
+            return err;
+        }
+
+        err = lfs2_dir_drop(lfs2, &newcwd, &prevdir);
+        if (err) {
+            LFS2_TRACE("lfs2_rename -> %d", err);
+            return err;
+        }
+    }
+
+    LFS2_TRACE("lfs2_rename -> %d", 0);
+    return 0;
+}
+
+lfs2_ssize_t lfs2_getattr(lfs2_t *lfs2, const char *path,
+        uint8_t type, void *buffer, lfs2_size_t size) {
+    LFS2_TRACE("lfs2_getattr(%p, \"%s\", %"PRIu8", %p, %"PRIu32")",
+            (void*)lfs2, path, type, buffer, size);
+    lfs2_mdir_t cwd;
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &cwd, &path, NULL);
+    if (tag < 0) {
+        LFS2_TRACE("lfs2_getattr -> %"PRId32, tag);
+        return tag;
+    }
+
+    uint16_t id = lfs2_tag_id(tag);
+    if (id == 0x3ff) {
+        // special case for root
+        id = 0;
+        int err = lfs2_dir_fetch(lfs2, &cwd, lfs2->root);
+        if (err) {
+            LFS2_TRACE("lfs2_getattr -> %"PRId32, err);
+            return err;
+        }
+    }
+
+    tag = lfs2_dir_get(lfs2, &cwd, LFS2_MKTAG(0x7ff, 0x3ff, 0),
+            LFS2_MKTAG(LFS2_TYPE_USERATTR + type,
+                id, lfs2_min(size, lfs2->attr_max)),
+            buffer);
+    if (tag < 0) {
+        if (tag == LFS2_ERR_NOENT) {
+            LFS2_TRACE("lfs2_getattr -> %"PRId32, LFS2_ERR_NOATTR);
+            return LFS2_ERR_NOATTR;
+        }
+
+        LFS2_TRACE("lfs2_getattr -> %"PRId32, tag);
+        return tag;
+    }
+
+    size = lfs2_tag_size(tag);
+    LFS2_TRACE("lfs2_getattr -> %"PRId32, size);
+    return size;
+}
+
+static int lfs2_commitattr(lfs2_t *lfs2, const char *path,
+        uint8_t type, const void *buffer, lfs2_size_t size) {
+    lfs2_mdir_t cwd;
+    lfs2_stag_t tag = lfs2_dir_find(lfs2, &cwd, &path, NULL);
+    if (tag < 0) {
+        return tag;
+    }
+
+    uint16_t id = lfs2_tag_id(tag);
+    if (id == 0x3ff) {
+        // special case for root
+        id = 0;
+        int err = lfs2_dir_fetch(lfs2, &cwd, lfs2->root);
+        if (err) {
+            return err;
+        }
+    }
+
+    return lfs2_dir_commit(lfs2, &cwd, LFS2_MKATTRS(
+            {LFS2_MKTAG(LFS2_TYPE_USERATTR + type, id, size), buffer}));
+}
+
+int lfs2_setattr(lfs2_t *lfs2, const char *path,
+        uint8_t type, const void *buffer, lfs2_size_t size) {
+    LFS2_TRACE("lfs2_setattr(%p, \"%s\", %"PRIu8", %p, %"PRIu32")",
+            (void*)lfs2, path, type, buffer, size);
+    if (size > lfs2->attr_max) {
+        LFS2_TRACE("lfs2_setattr -> %d", LFS2_ERR_NOSPC);
+        return LFS2_ERR_NOSPC;
+    }
+
+    int err = lfs2_commitattr(lfs2, path, type, buffer, size);
+    LFS2_TRACE("lfs2_setattr -> %d", err);
+    return err;
+}
+
+int lfs2_removeattr(lfs2_t *lfs2, const char *path, uint8_t type) {
+    LFS2_TRACE("lfs2_removeattr(%p, \"%s\", %"PRIu8")", (void*)lfs2, path, type);
+    int err = lfs2_commitattr(lfs2, path, type, NULL, 0x3ff);
+    LFS2_TRACE("lfs2_removeattr -> %d", err);
+    return err;
+}
+
+
+/// Filesystem operations ///
+static int lfs2_init(lfs2_t *lfs2, const struct lfs2_config *cfg) {
+    lfs2->cfg = cfg;
+    int err = 0;
+
+    // validate that the lfs2-cfg sizes were initiated properly before
+    // performing any arithmetic logics with them
+    LFS2_ASSERT(lfs2->cfg->read_size != 0);
+    LFS2_ASSERT(lfs2->cfg->prog_size != 0);
+    LFS2_ASSERT(lfs2->cfg->cache_size != 0);
+
+    // check that block size is a multiple of cache size is a multiple
+    // of prog and read sizes
+    LFS2_ASSERT(lfs2->cfg->cache_size % lfs2->cfg->read_size == 0);
+    LFS2_ASSERT(lfs2->cfg->cache_size % lfs2->cfg->prog_size == 0);
+    LFS2_ASSERT(lfs2->cfg->block_size % lfs2->cfg->cache_size == 0);
+
+    // check that the block size is large enough to fit ctz pointers
+    LFS2_ASSERT(4*lfs2_npw2(LFS2_BLOCK_NULL / (lfs2->cfg->block_size-2*4))
+            <= lfs2->cfg->block_size);
+
+    // block_cycles = 0 is no longer supported.
+    //
+    // block_cycles is the number of erase cycles before littlefs evicts
+    // metadata logs as a part of wear leveling. Suggested values are in the
+    // range of 100-1000, or set block_cycles to -1 to disable block-level
+    // wear-leveling.
+    LFS2_ASSERT(lfs2->cfg->block_cycles != 0);
+
+
+    // setup read cache
+    if (lfs2->cfg->read_buffer) {
+        lfs2->rcache.buffer = lfs2->cfg->read_buffer;
+    } else {
+        lfs2->rcache.buffer = lfs2_malloc(lfs2->cfg->cache_size);
+        if (!lfs2->rcache.buffer) {
+            err = LFS2_ERR_NOMEM;
+            goto cleanup;
+        }
+    }
+
+    // setup program cache
+    if (lfs2->cfg->prog_buffer) {
+        lfs2->pcache.buffer = lfs2->cfg->prog_buffer;
+    } else {
+        lfs2->pcache.buffer = lfs2_malloc(lfs2->cfg->cache_size);
+        if (!lfs2->pcache.buffer) {
+            err = LFS2_ERR_NOMEM;
+            goto cleanup;
+        }
+    }
+
+    // zero to avoid information leaks
+    lfs2_cache_zero(lfs2, &lfs2->rcache);
+    lfs2_cache_zero(lfs2, &lfs2->pcache);
+
+    // setup lookahead, must be multiple of 64-bits, 32-bit aligned
+    LFS2_ASSERT(lfs2->cfg->lookahead_size > 0);
+    LFS2_ASSERT(lfs2->cfg->lookahead_size % 8 == 0 &&
+            (uintptr_t)lfs2->cfg->lookahead_buffer % 4 == 0);
+    if (lfs2->cfg->lookahead_buffer) {
+        lfs2->free.buffer = lfs2->cfg->lookahead_buffer;
+    } else {
+        lfs2->free.buffer = lfs2_malloc(lfs2->cfg->lookahead_size);
+        if (!lfs2->free.buffer) {
+            err = LFS2_ERR_NOMEM;
+            goto cleanup;
+        }
+    }
+
+    // check that the size limits are sane
+    LFS2_ASSERT(lfs2->cfg->name_max <= LFS2_NAME_MAX);
+    lfs2->name_max = lfs2->cfg->name_max;
+    if (!lfs2->name_max) {
+        lfs2->name_max = LFS2_NAME_MAX;
+    }
+
+    LFS2_ASSERT(lfs2->cfg->file_max <= LFS2_FILE_MAX);
+    lfs2->file_max = lfs2->cfg->file_max;
+    if (!lfs2->file_max) {
+        lfs2->file_max = LFS2_FILE_MAX;
+    }
+
+    LFS2_ASSERT(lfs2->cfg->attr_max <= LFS2_ATTR_MAX);
+    lfs2->attr_max = lfs2->cfg->attr_max;
+    if (!lfs2->attr_max) {
+        lfs2->attr_max = LFS2_ATTR_MAX;
+    }
+
+    // setup default state
+    lfs2->root[0] = LFS2_BLOCK_NULL;
+    lfs2->root[1] = LFS2_BLOCK_NULL;
+    lfs2->mlist = NULL;
+    lfs2->seed = 0;
+    lfs2->gstate = (struct lfs2_gstate){0};
+    lfs2->gpending = (struct lfs2_gstate){0};
+    lfs2->gdelta = (struct lfs2_gstate){0};
+#ifdef LFS2_MIGRATE
+    lfs2->lfs21 = NULL;
+#endif
+
+    return 0;
+
+cleanup:
+    lfs2_deinit(lfs2);
+    return err;
+}
+
+static int lfs2_deinit(lfs2_t *lfs2) {
+    // free allocated memory
+    if (!lfs2->cfg->read_buffer) {
+        lfs2_free(lfs2->rcache.buffer);
+    }
+
+    if (!lfs2->cfg->prog_buffer) {
+        lfs2_free(lfs2->pcache.buffer);
+    }
+
+    if (!lfs2->cfg->lookahead_buffer) {
+        lfs2_free(lfs2->free.buffer);
+    }
+
+    return 0;
+}
+
+int lfs2_format(lfs2_t *lfs2, const struct lfs2_config *cfg) {
+    LFS2_TRACE("lfs2_format(%p, %p {.context=%p, "
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
+                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".block_size=%"PRIu32", .block_count=%"PRIu32", "
+                ".block_cycles=%"PRIu32", .cache_size=%"PRIu32", "
+                ".lookahead_size=%"PRIu32", .read_buffer=%p, "
+                ".prog_buffer=%p, .lookahead_buffer=%p, "
+                ".name_max=%"PRIu32", .file_max=%"PRIu32", "
+                ".attr_max=%"PRIu32"})",
+            (void*)lfs2, (void*)cfg, cfg->context,
+            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
+            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
+            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
+            cfg->block_cycles, cfg->cache_size, cfg->lookahead_size,
+            cfg->read_buffer, cfg->prog_buffer, cfg->lookahead_buffer,
+            cfg->name_max, cfg->file_max, cfg->attr_max);
+    int err = 0;
+    {
+        err = lfs2_init(lfs2, cfg);
+        if (err) {
+            LFS2_TRACE("lfs2_format -> %d", err);
+            return err;
+        }
+
+        // create free lookahead
+        memset(lfs2->free.buffer, 0, lfs2->cfg->lookahead_size);
+        lfs2->free.off = 0;
+        lfs2->free.size = lfs2_min(8*lfs2->cfg->lookahead_size,
+                lfs2->cfg->block_count);
+        lfs2->free.i = 0;
+        lfs2_alloc_ack(lfs2);
+
+        // create root dir
+        lfs2_mdir_t root;
+        err = lfs2_dir_alloc(lfs2, &root);
+        if (err) {
+            goto cleanup;
+        }
+
+        // write one superblock
+        lfs2_superblock_t superblock = {
+            .version     = LFS2_DISK_VERSION,
+            .block_size  = lfs2->cfg->block_size,
+            .block_count = lfs2->cfg->block_count,
+            .name_max    = lfs2->name_max,
+            .file_max    = lfs2->file_max,
+            .attr_max    = lfs2->attr_max,
+        };
+
+        lfs2_superblock_tole32(&superblock);
+        err = lfs2_dir_commit(lfs2, &root, LFS2_MKATTRS(
+                {LFS2_MKTAG(LFS2_TYPE_CREATE, 0, 0), NULL},
+                {LFS2_MKTAG(LFS2_TYPE_SUPERBLOCK, 0, 8), "littlefs"},
+                {LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
+                    &superblock}));
+        if (err) {
+            goto cleanup;
+        }
+
+        // sanity check that fetch works
+        err = lfs2_dir_fetch(lfs2, &root, (const lfs2_block_t[2]){0, 1});
+        if (err) {
+            goto cleanup;
+        }
+
+        // force compaction to prevent accidentally mounting any
+        // older version of littlefs that may live on disk
+        root.erased = false;
+        err = lfs2_dir_commit(lfs2, &root, NULL, 0);
+        if (err) {
+            goto cleanup;
+        }
+    }
+
+cleanup:
+    lfs2_deinit(lfs2);
+    LFS2_TRACE("lfs2_format -> %d", err);
+    return err;
+}
+
+int lfs2_mount(lfs2_t *lfs2, const struct lfs2_config *cfg) {
+    LFS2_TRACE("lfs2_mount(%p, %p {.context=%p, "
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
+                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".block_size=%"PRIu32", .block_count=%"PRIu32", "
+                ".block_cycles=%"PRIu32", .cache_size=%"PRIu32", "
+                ".lookahead_size=%"PRIu32", .read_buffer=%p, "
+                ".prog_buffer=%p, .lookahead_buffer=%p, "
+                ".name_max=%"PRIu32", .file_max=%"PRIu32", "
+                ".attr_max=%"PRIu32"})",
+            (void*)lfs2, (void*)cfg, cfg->context,
+            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
+            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
+            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
+            cfg->block_cycles, cfg->cache_size, cfg->lookahead_size,
+            cfg->read_buffer, cfg->prog_buffer, cfg->lookahead_buffer,
+            cfg->name_max, cfg->file_max, cfg->attr_max);
+    int err = lfs2_init(lfs2, cfg);
+    if (err) {
+        LFS2_TRACE("lfs2_mount -> %d", err);
+        return err;
+    }
+
+    // scan directory blocks for superblock and any global updates
+    lfs2_mdir_t dir = {.tail = {0, 1}};
+    while (!lfs2_pair_isnull(dir.tail)) {
+        // fetch next block in tail list
+        lfs2_stag_t tag = lfs2_dir_fetchmatch(lfs2, &dir, dir.tail,
+                LFS2_MKTAG(0x7ff, 0x3ff, 0),
+                LFS2_MKTAG(LFS2_TYPE_SUPERBLOCK, 0, 8),
+                NULL,
+                lfs2_dir_find_match, &(struct lfs2_dir_find_match){
+                    lfs2, "littlefs", 8});
+        if (tag < 0) {
+            err = tag;
+            goto cleanup;
+        }
+
+        // has superblock?
+        if (tag && !lfs2_tag_isdelete(tag)) {
+            // update root
+            lfs2->root[0] = dir.pair[0];
+            lfs2->root[1] = dir.pair[1];
+
+            // grab superblock
+            lfs2_superblock_t superblock;
+            tag = lfs2_dir_get(lfs2, &dir, LFS2_MKTAG(0x7ff, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
+                    &superblock);
+            if (tag < 0) {
+                err = tag;
+                goto cleanup;
+            }
+            lfs2_superblock_fromle32(&superblock);
+
+            // check version
+            uint16_t major_version = (0xffff & (superblock.version >> 16));
+            uint16_t minor_version = (0xffff & (superblock.version >>  0));
+            if ((major_version != LFS2_DISK_VERSION_MAJOR ||
+                 minor_version > LFS2_DISK_VERSION_MINOR)) {
+                LFS2_ERROR("Invalid version %"PRIu16".%"PRIu16,
+                        major_version, minor_version);
+                err = LFS2_ERR_INVAL;
+                goto cleanup;
+            }
+
+            // check superblock configuration
+            if (superblock.name_max) {
+                if (superblock.name_max > lfs2->name_max) {
+                    LFS2_ERROR("Unsupported name_max (%"PRIu32" > %"PRIu32")",
+                            superblock.name_max, lfs2->name_max);
+                    err = LFS2_ERR_INVAL;
+                    goto cleanup;
+                }
+
+                lfs2->name_max = superblock.name_max;
+            }
+
+            if (superblock.file_max) {
+                if (superblock.file_max > lfs2->file_max) {
+                    LFS2_ERROR("Unsupported file_max (%"PRIu32" > %"PRIu32")",
+                            superblock.file_max, lfs2->file_max);
+                    err = LFS2_ERR_INVAL;
+                    goto cleanup;
+                }
+
+                lfs2->file_max = superblock.file_max;
+            }
+
+            if (superblock.attr_max) {
+                if (superblock.attr_max > lfs2->attr_max) {
+                    LFS2_ERROR("Unsupported attr_max (%"PRIu32" > %"PRIu32")",
+                            superblock.attr_max, lfs2->attr_max);
+                    err = LFS2_ERR_INVAL;
+                    goto cleanup;
+                }
+
+                lfs2->attr_max = superblock.attr_max;
+            }
+        }
+
+        // has gstate?
+        err = lfs2_dir_getgstate(lfs2, &dir, &lfs2->gpending);
+        if (err) {
+            goto cleanup;
+        }
+    }
+
+    // found superblock?
+    if (lfs2_pair_isnull(lfs2->root)) {
+        err = LFS2_ERR_INVAL;
+        goto cleanup;
+    }
+
+    // update littlefs with gstate
+    lfs2->gpending.tag += !lfs2_tag_isvalid(lfs2->gpending.tag);
+    lfs2->gstate = lfs2->gpending;
+    if (lfs2_gstate_hasmove(&lfs2->gstate)) {
+        LFS2_DEBUG("Found move %"PRIx32" %"PRIx32" %"PRIx16,
+                lfs2->gstate.pair[0],
+                lfs2->gstate.pair[1],
+                lfs2_tag_id(lfs2->gstate.tag));
+    }
+
+    // setup free lookahead
+    lfs2->free.off = lfs2->seed % lfs2->cfg->block_size;
+    lfs2->free.size = 0;
+    lfs2->free.i = 0;
+    lfs2_alloc_ack(lfs2);
+
+    LFS2_TRACE("lfs2_mount -> %d", 0);
+    return 0;
+
+cleanup:
+    lfs2_unmount(lfs2);
+    LFS2_TRACE("lfs2_mount -> %d", err);
+    return err;
+}
+
+int lfs2_unmount(lfs2_t *lfs2) {
+    LFS2_TRACE("lfs2_unmount(%p)", (void*)lfs2);
+    int err = lfs2_deinit(lfs2);
+    LFS2_TRACE("lfs2_unmount -> %d", err);
+    return err;
+}
+
+
+/// Filesystem filesystem operations ///
+int lfs2_fs_traverse(lfs2_t *lfs2,
+        int (*cb)(void *data, lfs2_block_t block), void *data) {
+    LFS2_TRACE("lfs2_fs_traverse(%p, %p, %p)",
+            (void*)lfs2, (void*)(uintptr_t)cb, data);
+    // iterate over metadata pairs
+    lfs2_mdir_t dir = {.tail = {0, 1}};
+
+#ifdef LFS2_MIGRATE
+    // also consider v1 blocks during migration
+    if (lfs2->lfs21) {
+        int err = lfs21_traverse(lfs2, cb, data);
+        if (err) {
+            LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+            return err;
+        }
+
+        dir.tail[0] = lfs2->root[0];
+        dir.tail[1] = lfs2->root[1];
+    }
+#endif
+
+    while (!lfs2_pair_isnull(dir.tail)) {
+        for (int i = 0; i < 2; i++) {
+            int err = cb(data, dir.tail[i]);
+            if (err) {
+                LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+                return err;
+            }
+        }
+
+        // iterate through ids in directory
+        int err = lfs2_dir_fetch(lfs2, &dir, dir.tail);
+        if (err) {
+            LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+            return err;
+        }
+
+        for (uint16_t id = 0; id < dir.count; id++) {
+            struct lfs2_ctz ctz;
+            lfs2_stag_t tag = lfs2_dir_get(lfs2, &dir, LFS2_MKTAG(0x700, 0x3ff, 0),
+                    LFS2_MKTAG(LFS2_TYPE_STRUCT, id, sizeof(ctz)), &ctz);
+            if (tag < 0) {
+                if (tag == LFS2_ERR_NOENT) {
+                    continue;
+                }
+                LFS2_TRACE("lfs2_fs_traverse -> %d", tag);
+                return tag;
+            }
+            lfs2_ctz_fromle32(&ctz);
+
+            if (lfs2_tag_type3(tag) == LFS2_TYPE_CTZSTRUCT) {
+                err = lfs2_ctz_traverse(lfs2, NULL, &lfs2->rcache,
+                        ctz.head, ctz.size, cb, data);
+                if (err) {
+                    LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+                    return err;
+                }
+            }
+        }
+    }
+
+    // iterate over any open files
+    for (lfs2_file_t *f = (lfs2_file_t*)lfs2->mlist; f; f = f->next) {
+        if (f->type != LFS2_TYPE_REG) {
+            continue;
+        }
+
+        if ((f->flags & LFS2_F_DIRTY) && !(f->flags & LFS2_F_INLINE)) {
+            int err = lfs2_ctz_traverse(lfs2, &f->cache, &lfs2->rcache,
+                    f->ctz.head, f->ctz.size, cb, data);
+            if (err) {
+                LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+                return err;
+            }
+        }
+
+        if ((f->flags & LFS2_F_WRITING) && !(f->flags & LFS2_F_INLINE)) {
+            int err = lfs2_ctz_traverse(lfs2, &f->cache, &lfs2->rcache,
+                    f->block, f->pos, cb, data);
+            if (err) {
+                LFS2_TRACE("lfs2_fs_traverse -> %d", err);
+                return err;
+            }
+        }
+    }
+
+    LFS2_TRACE("lfs2_fs_traverse -> %d", 0);
+    return 0;
+}
+
+static int lfs2_fs_pred(lfs2_t *lfs2,
+        const lfs2_block_t pair[2], lfs2_mdir_t *pdir) {
+    // iterate over all directory directory entries
+    pdir->tail[0] = 0;
+    pdir->tail[1] = 1;
+    while (!lfs2_pair_isnull(pdir->tail)) {
+        if (lfs2_pair_cmp(pdir->tail, pair) == 0) {
+            return 0;
+        }
+
+        int err = lfs2_dir_fetch(lfs2, pdir, pdir->tail);
+        if (err) {
+            return err;
+        }
+    }
+
+    return LFS2_ERR_NOENT;
+}
+
+struct lfs2_fs_parent_match {
+    lfs2_t *lfs2;
+    const lfs2_block_t pair[2];
+};
+
+static int lfs2_fs_parent_match(void *data,
+        lfs2_tag_t tag, const void *buffer) {
+    struct lfs2_fs_parent_match *find = data;
+    lfs2_t *lfs2 = find->lfs2;
+    const struct lfs2_diskoff *disk = buffer;
+    (void)tag;
+
+    lfs2_block_t child[2];
+    int err = lfs2_bd_read(lfs2,
+            &lfs2->pcache, &lfs2->rcache, lfs2->cfg->block_size,
+            disk->block, disk->off, &child, sizeof(child));
+    if (err) {
+        return err;
+    }
+
+    lfs2_pair_fromle32(child);
+    return (lfs2_pair_cmp(child, find->pair) == 0) ? LFS2_CMP_EQ : LFS2_CMP_LT;
+}
+
+static lfs2_stag_t lfs2_fs_parent(lfs2_t *lfs2, const lfs2_block_t pair[2],
+        lfs2_mdir_t *parent) {
+    // use fetchmatch with callback to find pairs
+    parent->tail[0] = 0;
+    parent->tail[1] = 1;
+    while (!lfs2_pair_isnull(parent->tail)) {
+        lfs2_stag_t tag = lfs2_dir_fetchmatch(lfs2, parent, parent->tail,
+                LFS2_MKTAG(0x7ff, 0, 0x3ff),
+                LFS2_MKTAG(LFS2_TYPE_DIRSTRUCT, 0, 8),
+                NULL,
+                lfs2_fs_parent_match, &(struct lfs2_fs_parent_match){
+                    lfs2, {pair[0], pair[1]}});
+        if (tag && tag != LFS2_ERR_NOENT) {
+            return tag;
+        }
+    }
+
+    return LFS2_ERR_NOENT;
+}
+
+static int lfs2_fs_relocate(lfs2_t *lfs2,
+        const lfs2_block_t oldpair[2], lfs2_block_t newpair[2]) {
+    // update internal root
+    if (lfs2_pair_cmp(oldpair, lfs2->root) == 0) {
+        LFS2_DEBUG("Relocating root %"PRIx32" %"PRIx32,
+                newpair[0], newpair[1]);
+        lfs2->root[0] = newpair[0];
+        lfs2->root[1] = newpair[1];
+    }
+
+    // update internally tracked dirs
+    for (struct lfs2_mlist *d = lfs2->mlist; d; d = d->next) {
+        if (lfs2_pair_cmp(oldpair, d->m.pair) == 0) {
+            d->m.pair[0] = newpair[0];
+            d->m.pair[1] = newpair[1];
+        }
+    }
+
+    // find parent
+    lfs2_mdir_t parent;
+    lfs2_stag_t tag = lfs2_fs_parent(lfs2, oldpair, &parent);
+    if (tag < 0 && tag != LFS2_ERR_NOENT) {
+        return tag;
+    }
+
+    if (tag != LFS2_ERR_NOENT) {
+        // update disk, this creates a desync
+        lfs2_fs_preporphans(lfs2, +1);
+
+        lfs2_pair_tole32(newpair);
+        int err = lfs2_dir_commit(lfs2, &parent, LFS2_MKATTRS({tag, newpair}));
+        lfs2_pair_fromle32(newpair);
+        if (err) {
+            return err;
+        }
+
+        // next step, clean up orphans
+        lfs2_fs_preporphans(lfs2, -1);
+    }
+
+    // find pred
+    int err = lfs2_fs_pred(lfs2, oldpair, &parent);
+    if (err && err != LFS2_ERR_NOENT) {
+        return err;
+    }
+
+    // if we can't find dir, it must be new
+    if (err != LFS2_ERR_NOENT) {
+        // replace bad pair, either we clean up desync, or no desync occured
+        lfs2_pair_tole32(newpair);
+        err = lfs2_dir_commit(lfs2, &parent, LFS2_MKATTRS(
+                {LFS2_MKTAG(LFS2_TYPE_TAIL + parent.split, 0x3ff, 8), newpair}));
+        lfs2_pair_fromle32(newpair);
+        if (err) {
+            return err;
+        }
+    }
+
+    return 0;
+}
+
+static void lfs2_fs_preporphans(lfs2_t *lfs2, int8_t orphans) {
+    lfs2->gpending.tag += orphans;
+    lfs2_gstate_xororphans(&lfs2->gdelta,   &lfs2->gpending,
+            lfs2_gstate_hasorphans(&lfs2->gpending));
+    lfs2_gstate_xororphans(&lfs2->gpending, &lfs2->gpending,
+            lfs2_gstate_hasorphans(&lfs2->gpending));
+}
+
+static void lfs2_fs_prepmove(lfs2_t *lfs2,
+        uint16_t id, const lfs2_block_t pair[2]) {
+    lfs2_gstate_xormove(&lfs2->gdelta,   &lfs2->gpending, id, pair);
+    lfs2_gstate_xormove(&lfs2->gpending, &lfs2->gpending, id, pair);
+}
+
+
+static int lfs2_fs_demove(lfs2_t *lfs2) {
+    if (!lfs2_gstate_hasmove(&lfs2->gstate)) {
+        return 0;
+    }
+
+    // Fix bad moves
+    LFS2_DEBUG("Fixing move %"PRIx32" %"PRIx32" %"PRIx16,
+            lfs2->gstate.pair[0],
+            lfs2->gstate.pair[1],
+            lfs2_tag_id(lfs2->gstate.tag));
+
+    // fetch and delete the moved entry
+    lfs2_mdir_t movedir;
+    int err = lfs2_dir_fetch(lfs2, &movedir, lfs2->gstate.pair);
+    if (err) {
+        return err;
+    }
+
+    // rely on cancel logic inside commit
+    err = lfs2_dir_commit(lfs2, &movedir, NULL, 0);
+    if (err) {
+        return err;
+    }
+
+    return 0;
+}
+
+static int lfs2_fs_deorphan(lfs2_t *lfs2) {
+    if (!lfs2_gstate_hasorphans(&lfs2->gstate)) {
+        return 0;
+    }
+
+    // Fix any orphans
+    lfs2_mdir_t pdir = {.split = true};
+    lfs2_mdir_t dir = {.tail = {0, 1}};
+
+    // iterate over all directory directory entries
+    while (!lfs2_pair_isnull(dir.tail)) {
+        int err = lfs2_dir_fetch(lfs2, &dir, dir.tail);
+        if (err) {
+            return err;
+        }
+
+        // check head blocks for orphans
+        if (!pdir.split) {
+            // check if we have a parent
+            lfs2_mdir_t parent;
+            lfs2_stag_t tag = lfs2_fs_parent(lfs2, pdir.tail, &parent);
+            if (tag < 0 && tag != LFS2_ERR_NOENT) {
+                return tag;
+            }
+
+            if (tag == LFS2_ERR_NOENT) {
+                // we are an orphan
+                LFS2_DEBUG("Fixing orphan %"PRIx32" %"PRIx32,
+                        pdir.tail[0], pdir.tail[1]);
+
+                err = lfs2_dir_drop(lfs2, &pdir, &dir);
+                if (err) {
+                    return err;
+                }
+
+                break;
+            }
+
+            lfs2_block_t pair[2];
+            lfs2_stag_t res = lfs2_dir_get(lfs2, &parent,
+                    LFS2_MKTAG(0x7ff, 0x3ff, 0), tag, pair);
+            if (res < 0) {
+                return res;
+            }
+            lfs2_pair_fromle32(pair);
+
+            if (!lfs2_pair_sync(pair, pdir.tail)) {
+                // we have desynced
+                LFS2_DEBUG("Fixing half-orphan %"PRIx32" %"PRIx32,
+                        pair[0], pair[1]);
+
+                lfs2_pair_tole32(pair);
+                err = lfs2_dir_commit(lfs2, &pdir, LFS2_MKATTRS(
+                        {LFS2_MKTAG(LFS2_TYPE_SOFTTAIL, 0x3ff, 8), pair}));
+                lfs2_pair_fromle32(pair);
+                if (err) {
+                    return err;
+                }
+
+                break;
+            }
+        }
+
+        memcpy(&pdir, &dir, sizeof(pdir));
+    }
+
+    // mark orphans as fixed
+    lfs2_fs_preporphans(lfs2, -lfs2_gstate_getorphans(&lfs2->gstate));
+    lfs2->gstate = lfs2->gpending;
+    return 0;
+}
+
+static int lfs2_fs_forceconsistency(lfs2_t *lfs2) {
+    int err = lfs2_fs_demove(lfs2);
+    if (err) {
+        return err;
+    }
+
+    err = lfs2_fs_deorphan(lfs2);
+    if (err) {
+        return err;
+    }
+
+    return 0;
+}
+
+static int lfs2_fs_size_count(void *p, lfs2_block_t block) {
+    (void)block;
+    lfs2_size_t *size = p;
+    *size += 1;
+    return 0;
+}
+
+lfs2_ssize_t lfs2_fs_size(lfs2_t *lfs2) {
+    LFS2_TRACE("lfs2_fs_size(%p)", (void*)lfs2);
+    lfs2_size_t size = 0;
+    int err = lfs2_fs_traverse(lfs2, lfs2_fs_size_count, &size);
+    if (err) {
+        LFS2_TRACE("lfs2_fs_size -> %"PRId32, err);
+        return err;
+    }
+
+    LFS2_TRACE("lfs2_fs_size -> %"PRId32, err);
+    return size;
+}
+
+#ifdef LFS2_MIGRATE
+////// Migration from littelfs v1 below this //////
+
+/// Version info ///
+
+// Software library version
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS21_VERSION 0x00010007
+#define LFS21_VERSION_MAJOR (0xffff & (LFS21_VERSION >> 16))
+#define LFS21_VERSION_MINOR (0xffff & (LFS21_VERSION >>  0))
+
+// Version of On-disk data structures
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS21_DISK_VERSION 0x00010001
+#define LFS21_DISK_VERSION_MAJOR (0xffff & (LFS21_DISK_VERSION >> 16))
+#define LFS21_DISK_VERSION_MINOR (0xffff & (LFS21_DISK_VERSION >>  0))
+
+
+/// v1 Definitions ///
+
+// File types
+enum lfs21_type {
+    LFS21_TYPE_REG        = 0x11,
+    LFS21_TYPE_DIR        = 0x22,
+    LFS21_TYPE_SUPERBLOCK = 0x2e,
+};
+
+typedef struct lfs21 {
+    lfs2_block_t root[2];
+} lfs21_t;
+
+typedef struct lfs21_entry {
+    lfs2_off_t off;
+
+    struct lfs21_disk_entry {
+        uint8_t type;
+        uint8_t elen;
+        uint8_t alen;
+        uint8_t nlen;
+        union {
+            struct {
+                lfs2_block_t head;
+                lfs2_size_t size;
+            } file;
+            lfs2_block_t dir[2];
+        } u;
+    } d;
+} lfs21_entry_t;
+
+typedef struct lfs21_dir {
+    struct lfs21_dir *next;
+    lfs2_block_t pair[2];
+    lfs2_off_t off;
+
+    lfs2_block_t head[2];
+    lfs2_off_t pos;
+
+    struct lfs21_disk_dir {
+        uint32_t rev;
+        lfs2_size_t size;
+        lfs2_block_t tail[2];
+    } d;
+} lfs21_dir_t;
+
+typedef struct lfs21_superblock {
+    lfs2_off_t off;
+
+    struct lfs21_disk_superblock {
+        uint8_t type;
+        uint8_t elen;
+        uint8_t alen;
+        uint8_t nlen;
+        lfs2_block_t root[2];
+        uint32_t block_size;
+        uint32_t block_count;
+        uint32_t version;
+        char magic[8];
+    } d;
+} lfs21_superblock_t;
+
+
+/// Low-level wrappers v1->v2 ///
+static void lfs21_crc(uint32_t *crc, const void *buffer, size_t size) {
+    *crc = lfs2_crc(*crc, buffer, size);
+}
+
+static int lfs21_bd_read(lfs2_t *lfs2, lfs2_block_t block,
+        lfs2_off_t off, void *buffer, lfs2_size_t size) {
+    // if we ever do more than writes to alternating pairs,
+    // this may need to consider pcache
+    return lfs2_bd_read(lfs2, &lfs2->pcache, &lfs2->rcache, size,
+            block, off, buffer, size);
+}
+
+static int lfs21_bd_crc(lfs2_t *lfs2, lfs2_block_t block,
+        lfs2_off_t off, lfs2_size_t size, uint32_t *crc) {
+    for (lfs2_off_t i = 0; i < size; i++) {
+        uint8_t c;
+        int err = lfs21_bd_read(lfs2, block, off+i, &c, 1);
+        if (err) {
+            return err;
+        }
+
+        lfs21_crc(crc, &c, 1);
+    }
+
+    return 0;
+}
+
+
+/// Endian swapping functions ///
+static void lfs21_dir_fromle32(struct lfs21_disk_dir *d) {
+    d->rev     = lfs2_fromle32(d->rev);
+    d->size    = lfs2_fromle32(d->size);
+    d->tail[0] = lfs2_fromle32(d->tail[0]);
+    d->tail[1] = lfs2_fromle32(d->tail[1]);
+}
+
+static void lfs21_dir_tole32(struct lfs21_disk_dir *d) {
+    d->rev     = lfs2_tole32(d->rev);
+    d->size    = lfs2_tole32(d->size);
+    d->tail[0] = lfs2_tole32(d->tail[0]);
+    d->tail[1] = lfs2_tole32(d->tail[1]);
+}
+
+static void lfs21_entry_fromle32(struct lfs21_disk_entry *d) {
+    d->u.dir[0] = lfs2_fromle32(d->u.dir[0]);
+    d->u.dir[1] = lfs2_fromle32(d->u.dir[1]);
+}
+
+static void lfs21_entry_tole32(struct lfs21_disk_entry *d) {
+    d->u.dir[0] = lfs2_tole32(d->u.dir[0]);
+    d->u.dir[1] = lfs2_tole32(d->u.dir[1]);
+}
+
+static void lfs21_superblock_fromle32(struct lfs21_disk_superblock *d) {
+    d->root[0]     = lfs2_fromle32(d->root[0]);
+    d->root[1]     = lfs2_fromle32(d->root[1]);
+    d->block_size  = lfs2_fromle32(d->block_size);
+    d->block_count = lfs2_fromle32(d->block_count);
+    d->version     = lfs2_fromle32(d->version);
+}
+
+
+///// Metadata pair and directory operations ///
+static inline lfs2_size_t lfs21_entry_size(const lfs21_entry_t *entry) {
+    return 4 + entry->d.elen + entry->d.alen + entry->d.nlen;
+}
+
+static int lfs21_dir_fetch(lfs2_t *lfs2,
+        lfs21_dir_t *dir, const lfs2_block_t pair[2]) {
+    // copy out pair, otherwise may be aliasing dir
+    const lfs2_block_t tpair[2] = {pair[0], pair[1]};
+    bool valid = false;
+
+    // check both blocks for the most recent revision
+    for (int i = 0; i < 2; i++) {
+        struct lfs21_disk_dir test;
+        int err = lfs21_bd_read(lfs2, tpair[i], 0, &test, sizeof(test));
+        lfs21_dir_fromle32(&test);
+        if (err) {
+            if (err == LFS2_ERR_CORRUPT) {
+                continue;
+            }
+            return err;
+        }
+
+        if (valid && lfs2_scmp(test.rev, dir->d.rev) < 0) {
+            continue;
+        }
+
+        if ((0x7fffffff & test.size) < sizeof(test)+4 ||
+            (0x7fffffff & test.size) > lfs2->cfg->block_size) {
+            continue;
+        }
+
+        uint32_t crc = LFS2_BLOCK_NULL;
+        lfs21_dir_tole32(&test);
+        lfs21_crc(&crc, &test, sizeof(test));
+        lfs21_dir_fromle32(&test);
+        err = lfs21_bd_crc(lfs2, tpair[i], sizeof(test),
+                (0x7fffffff & test.size) - sizeof(test), &crc);
+        if (err) {
+            if (err == LFS2_ERR_CORRUPT) {
+                continue;
+            }
+            return err;
+        }
+
+        if (crc != 0) {
+            continue;
+        }
+
+        valid = true;
+
+        // setup dir in case it's valid
+        dir->pair[0] = tpair[(i+0) % 2];
+        dir->pair[1] = tpair[(i+1) % 2];
+        dir->off = sizeof(dir->d);
+        dir->d = test;
+    }
+
+    if (!valid) {
+        LFS2_ERROR("Corrupted dir pair at %" PRIx32 " %" PRIx32 ,
+                tpair[0], tpair[1]);
+        return LFS2_ERR_CORRUPT;
+    }
+
+    return 0;
+}
+
+static int lfs21_dir_next(lfs2_t *lfs2, lfs21_dir_t *dir, lfs21_entry_t *entry) {
+    while (dir->off + sizeof(entry->d) > (0x7fffffff & dir->d.size)-4) {
+        if (!(0x80000000 & dir->d.size)) {
+            entry->off = dir->off;
+            return LFS2_ERR_NOENT;
+        }
+
+        int err = lfs21_dir_fetch(lfs2, dir, dir->d.tail);
+        if (err) {
+            return err;
+        }
+
+        dir->off = sizeof(dir->d);
+        dir->pos += sizeof(dir->d) + 4;
+    }
+
+    int err = lfs21_bd_read(lfs2, dir->pair[0], dir->off,
+            &entry->d, sizeof(entry->d));
+    lfs21_entry_fromle32(&entry->d);
+    if (err) {
+        return err;
+    }
+
+    entry->off = dir->off;
+    dir->off += lfs21_entry_size(entry);
+    dir->pos += lfs21_entry_size(entry);
+    return 0;
+}
+
+/// littlefs v1 specific operations ///
+int lfs21_traverse(lfs2_t *lfs2, int (*cb)(void*, lfs2_block_t), void *data) {
+    if (lfs2_pair_isnull(lfs2->lfs21->root)) {
+        return 0;
+    }
+
+    // iterate over metadata pairs
+    lfs21_dir_t dir;
+    lfs21_entry_t entry;
+    lfs2_block_t cwd[2] = {0, 1};
+
+    while (true) {
+        for (int i = 0; i < 2; i++) {
+            int err = cb(data, cwd[i]);
+            if (err) {
+                return err;
+            }
+        }
+
+        int err = lfs21_dir_fetch(lfs2, &dir, cwd);
+        if (err) {
+            return err;
+        }
+
+        // iterate over contents
+        while (dir.off + sizeof(entry.d) <= (0x7fffffff & dir.d.size)-4) {
+            err = lfs21_bd_read(lfs2, dir.pair[0], dir.off,
+                    &entry.d, sizeof(entry.d));
+            lfs21_entry_fromle32(&entry.d);
+            if (err) {
+                return err;
+            }
+
+            dir.off += lfs21_entry_size(&entry);
+            if ((0x70 & entry.d.type) == (0x70 & LFS21_TYPE_REG)) {
+                err = lfs2_ctz_traverse(lfs2, NULL, &lfs2->rcache,
+                        entry.d.u.file.head, entry.d.u.file.size, cb, data);
+                if (err) {
+                    return err;
+                }
+            }
+        }
+
+        // we also need to check if we contain a threaded v2 directory
+        lfs2_mdir_t dir2 = {.split=true, .tail={cwd[0], cwd[1]}};
+        while (dir2.split) {
+            err = lfs2_dir_fetch(lfs2, &dir2, dir2.tail);
+            if (err) {
+                break;
+            }
+
+            for (int i = 0; i < 2; i++) {
+                err = cb(data, dir2.pair[i]);
+                if (err) {
+                    return err;
+                }
+            }
+        }
+
+        cwd[0] = dir.d.tail[0];
+        cwd[1] = dir.d.tail[1];
+
+        if (lfs2_pair_isnull(cwd)) {
+            break;
+        }
+    }
+
+    return 0;
+}
+
+static int lfs21_moved(lfs2_t *lfs2, const void *e) {
+    if (lfs2_pair_isnull(lfs2->lfs21->root)) {
+        return 0;
+    }
+
+    // skip superblock
+    lfs21_dir_t cwd;
+    int err = lfs21_dir_fetch(lfs2, &cwd, (const lfs2_block_t[2]){0, 1});
+    if (err) {
+        return err;
+    }
+
+    // iterate over all directory directory entries
+    lfs21_entry_t entry;
+    while (!lfs2_pair_isnull(cwd.d.tail)) {
+        err = lfs21_dir_fetch(lfs2, &cwd, cwd.d.tail);
+        if (err) {
+            return err;
+        }
+
+        while (true) {
+            err = lfs21_dir_next(lfs2, &cwd, &entry);
+            if (err && err != LFS2_ERR_NOENT) {
+                return err;
+            }
+
+            if (err == LFS2_ERR_NOENT) {
+                break;
+            }
+
+            if (!(0x80 & entry.d.type) &&
+                 memcmp(&entry.d.u, e, sizeof(entry.d.u)) == 0) {
+                return true;
+            }
+        }
+    }
+
+    return false;
+}
+
+/// Filesystem operations ///
+static int lfs21_mount(lfs2_t *lfs2, struct lfs21 *lfs21,
+        const struct lfs2_config *cfg) {
+    int err = 0;
+    {
+        err = lfs2_init(lfs2, cfg);
+        if (err) {
+            return err;
+        }
+
+        lfs2->lfs21 = lfs21;
+        lfs2->lfs21->root[0] = LFS2_BLOCK_NULL;
+        lfs2->lfs21->root[1] = LFS2_BLOCK_NULL;
+
+        // setup free lookahead
+        lfs2->free.off = 0;
+        lfs2->free.size = 0;
+        lfs2->free.i = 0;
+        lfs2_alloc_ack(lfs2);
+
+        // load superblock
+        lfs21_dir_t dir;
+        lfs21_superblock_t superblock;
+        err = lfs21_dir_fetch(lfs2, &dir, (const lfs2_block_t[2]){0, 1});
+        if (err && err != LFS2_ERR_CORRUPT) {
+            goto cleanup;
+        }
+
+        if (!err) {
+            err = lfs21_bd_read(lfs2, dir.pair[0], sizeof(dir.d),
+                    &superblock.d, sizeof(superblock.d));
+            lfs21_superblock_fromle32(&superblock.d);
+            if (err) {
+                goto cleanup;
+            }
+
+            lfs2->lfs21->root[0] = superblock.d.root[0];
+            lfs2->lfs21->root[1] = superblock.d.root[1];
+        }
+
+        if (err || memcmp(superblock.d.magic, "littlefs", 8) != 0) {
+            LFS2_ERROR("Invalid superblock at %d %d", 0, 1);
+            err = LFS2_ERR_CORRUPT;
+            goto cleanup;
+        }
+
+        uint16_t major_version = (0xffff & (superblock.d.version >> 16));
+        uint16_t minor_version = (0xffff & (superblock.d.version >>  0));
+        if ((major_version != LFS21_DISK_VERSION_MAJOR ||
+             minor_version > LFS21_DISK_VERSION_MINOR)) {
+            LFS2_ERROR("Invalid version %d.%d", major_version, minor_version);
+            err = LFS2_ERR_INVAL;
+            goto cleanup;
+        }
+
+        return 0;
+    }
+
+cleanup:
+    lfs2_deinit(lfs2);
+    return err;
+}
+
+static int lfs21_unmount(lfs2_t *lfs2) {
+    return lfs2_deinit(lfs2);
+}
+
+/// v1 migration ///
+int lfs2_migrate(lfs2_t *lfs2, const struct lfs2_config *cfg) {
+    LFS2_TRACE("lfs2_migrate(%p, %p {.context=%p, "
+                ".read=%p, .prog=%p, .erase=%p, .sync=%p, "
+                ".read_size=%"PRIu32", .prog_size=%"PRIu32", "
+                ".block_size=%"PRIu32", .block_count=%"PRIu32", "
+                ".block_cycles=%"PRIu32", .cache_size=%"PRIu32", "
+                ".lookahead_size=%"PRIu32", .read_buffer=%p, "
+                ".prog_buffer=%p, .lookahead_buffer=%p, "
+                ".name_max=%"PRIu32", .file_max=%"PRIu32", "
+                ".attr_max=%"PRIu32"})",
+            (void*)lfs2, (void*)cfg, cfg->context,
+            (void*)(uintptr_t)cfg->read, (void*)(uintptr_t)cfg->prog,
+            (void*)(uintptr_t)cfg->erase, (void*)(uintptr_t)cfg->sync,
+            cfg->read_size, cfg->prog_size, cfg->block_size, cfg->block_count,
+            cfg->block_cycles, cfg->cache_size, cfg->lookahead_size,
+            cfg->read_buffer, cfg->prog_buffer, cfg->lookahead_buffer,
+            cfg->name_max, cfg->file_max, cfg->attr_max);
+    struct lfs21 lfs21;
+    int err = lfs21_mount(lfs2, &lfs21, cfg);
+    if (err) {
+        LFS2_TRACE("lfs2_migrate -> %d", err);
+        return err;
+    }
+
+    {
+        // iterate through each directory, copying over entries
+        // into new directory
+        lfs21_dir_t dir1;
+        lfs2_mdir_t dir2;
+        dir1.d.tail[0] = lfs2->lfs21->root[0];
+        dir1.d.tail[1] = lfs2->lfs21->root[1];
+        while (!lfs2_pair_isnull(dir1.d.tail)) {
+            // iterate old dir
+            err = lfs21_dir_fetch(lfs2, &dir1, dir1.d.tail);
+            if (err) {
+                goto cleanup;
+            }
+
+            // create new dir and bind as temporary pretend root
+            err = lfs2_dir_alloc(lfs2, &dir2);
+            if (err) {
+                goto cleanup;
+            }
+
+            dir2.rev = dir1.d.rev;
+            dir1.head[0] = dir1.pair[0];
+            dir1.head[1] = dir1.pair[1];
+            lfs2->root[0] = dir2.pair[0];
+            lfs2->root[1] = dir2.pair[1];
+
+            err = lfs2_dir_commit(lfs2, &dir2, NULL, 0);
+            if (err) {
+                goto cleanup;
+            }
+
+            while (true) {
+                lfs21_entry_t entry1;
+                err = lfs21_dir_next(lfs2, &dir1, &entry1);
+                if (err && err != LFS2_ERR_NOENT) {
+                    goto cleanup;
+                }
+
+                if (err == LFS2_ERR_NOENT) {
+                    break;
+                }
+
+                // check that entry has not been moved
+                if (entry1.d.type & 0x80) {
+                    int moved = lfs21_moved(lfs2, &entry1.d.u);
+                    if (moved < 0) {
+                        err = moved;
+                        goto cleanup;
+                    }
+
+                    if (moved) {
+                        continue;
+                    }
+
+                    entry1.d.type &= ~0x80;
+                }
+
+                // also fetch name
+                char name[LFS2_NAME_MAX+1];
+                memset(name, 0, sizeof(name));
+                err = lfs21_bd_read(lfs2, dir1.pair[0],
+                        entry1.off + 4+entry1.d.elen+entry1.d.alen,
+                        name, entry1.d.nlen);
+                if (err) {
+                    goto cleanup;
+                }
+
+                bool isdir = (entry1.d.type == LFS21_TYPE_DIR);
+
+                // create entry in new dir
+                err = lfs2_dir_fetch(lfs2, &dir2, lfs2->root);
+                if (err) {
+                    goto cleanup;
+                }
+
+                uint16_t id;
+                err = lfs2_dir_find(lfs2, &dir2, &(const char*){name}, &id);
+                if (!(err == LFS2_ERR_NOENT && id != 0x3ff)) {
+                    err = (err < 0) ? err : LFS2_ERR_EXIST;
+                    goto cleanup;
+                }
+
+                lfs21_entry_tole32(&entry1.d);
+                err = lfs2_dir_commit(lfs2, &dir2, LFS2_MKATTRS(
+                        {LFS2_MKTAG(LFS2_TYPE_CREATE, id, 0), NULL},
+                        {LFS2_MKTAG(
+                            isdir ? LFS2_TYPE_DIR : LFS2_TYPE_REG,
+                            id, entry1.d.nlen), name},
+                        {LFS2_MKTAG(
+                            isdir ? LFS2_TYPE_DIRSTRUCT : LFS2_TYPE_CTZSTRUCT,
+                            id, sizeof(&entry1.d.u)), &entry1.d.u}));
+                lfs21_entry_fromle32(&entry1.d);
+                if (err) {
+                    goto cleanup;
+                }
+            }
+
+            if (!lfs2_pair_isnull(dir1.d.tail)) {
+                // find last block and update tail to thread into fs
+                err = lfs2_dir_fetch(lfs2, &dir2, lfs2->root);
+                if (err) {
+                    goto cleanup;
+                }
+
+                while (dir2.split) {
+                    err = lfs2_dir_fetch(lfs2, &dir2, dir2.tail);
+                    if (err) {
+                        goto cleanup;
+                    }
+                }
+
+                lfs2_pair_tole32(dir2.pair);
+                err = lfs2_dir_commit(lfs2, &dir2, LFS2_MKATTRS(
+                        {LFS2_MKTAG(LFS2_TYPE_SOFTTAIL, 0x3ff, 0),
+                            dir1.d.tail}));
+                lfs2_pair_fromle32(dir2.pair);
+                if (err) {
+                    goto cleanup;
+                }
+            }
+
+            // Copy over first block to thread into fs. Unfortunately
+            // if this fails there is not much we can do.
+            LFS2_DEBUG("Migrating %"PRIx32" %"PRIx32" -> %"PRIx32" %"PRIx32,
+                    lfs2->root[0], lfs2->root[1], dir1.head[0], dir1.head[1]);
+
+            err = lfs2_bd_erase(lfs2, dir1.head[1]);
+            if (err) {
+                goto cleanup;
+            }
+
+            err = lfs2_dir_fetch(lfs2, &dir2, lfs2->root);
+            if (err) {
+                goto cleanup;
+            }
+
+            for (lfs2_off_t i = 0; i < dir2.off; i++) {
+                uint8_t dat;
+                err = lfs2_bd_read(lfs2,
+                        NULL, &lfs2->rcache, dir2.off,
+                        dir2.pair[0], i, &dat, 1);
+                if (err) {
+                    goto cleanup;
+                }
+
+                err = lfs2_bd_prog(lfs2,
+                        &lfs2->pcache, &lfs2->rcache, true,
+                        dir1.head[1], i, &dat, 1);
+                if (err) {
+                    goto cleanup;
+                }
+            }
+
+            err = lfs2_bd_flush(lfs2, &lfs2->pcache, &lfs2->rcache, true);
+            if (err) {
+                goto cleanup;
+            }
+        }
+
+        // Create new superblock. This marks a successful migration!
+        err = lfs21_dir_fetch(lfs2, &dir1, (const lfs2_block_t[2]){0, 1});
+        if (err) {
+            goto cleanup;
+        }
+
+        dir2.pair[0] = dir1.pair[0];
+        dir2.pair[1] = dir1.pair[1];
+        dir2.rev = dir1.d.rev;
+        dir2.off = sizeof(dir2.rev);
+        dir2.etag = LFS2_BLOCK_NULL;
+        dir2.count = 0;
+        dir2.tail[0] = lfs2->lfs21->root[0];
+        dir2.tail[1] = lfs2->lfs21->root[1];
+        dir2.erased = false;
+        dir2.split = true;
+
+        lfs2_superblock_t superblock = {
+            .version     = LFS2_DISK_VERSION,
+            .block_size  = lfs2->cfg->block_size,
+            .block_count = lfs2->cfg->block_count,
+            .name_max    = lfs2->name_max,
+            .file_max    = lfs2->file_max,
+            .attr_max    = lfs2->attr_max,
+        };
+
+        lfs2_superblock_tole32(&superblock);
+        err = lfs2_dir_commit(lfs2, &dir2, LFS2_MKATTRS(
+                {LFS2_MKTAG(LFS2_TYPE_CREATE, 0, 0), NULL},
+                {LFS2_MKTAG(LFS2_TYPE_SUPERBLOCK, 0, 8), "littlefs"},
+                {LFS2_MKTAG(LFS2_TYPE_INLINESTRUCT, 0, sizeof(superblock)),
+                    &superblock}));
+        if (err) {
+            goto cleanup;
+        }
+
+        // sanity check that fetch works
+        err = lfs2_dir_fetch(lfs2, &dir2, (const lfs2_block_t[2]){0, 1});
+        if (err) {
+            goto cleanup;
+        }
+
+        // force compaction to prevent accidentally mounting v1
+        dir2.erased = false;
+        err = lfs2_dir_commit(lfs2, &dir2, NULL, 0);
+        if (err) {
+            goto cleanup;
+        }
+    }
+
+cleanup:
+    lfs21_unmount(lfs2);
+    LFS2_TRACE("lfs2_migrate -> %d", err);
+    return err;
+}
+
+#endif
diff --git a/lib/littlefs/lfs2.h b/lib/littlefs/lfs2.h
new file mode 100644
index 0000000000..fdbe007cc9
--- /dev/null
+++ b/lib/littlefs/lfs2.h
@@ -0,0 +1,651 @@
+/*
+ * The little filesystem
+ *
+ * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#ifndef LFS2_H
+#define LFS2_H
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+
+/// Version info ///
+
+// Software library version
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS2_VERSION 0x00020001
+#define LFS2_VERSION_MAJOR (0xffff & (LFS2_VERSION >> 16))
+#define LFS2_VERSION_MINOR (0xffff & (LFS2_VERSION >>  0))
+
+// Version of On-disk data structures
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS2_DISK_VERSION 0x00020000
+#define LFS2_DISK_VERSION_MAJOR (0xffff & (LFS2_DISK_VERSION >> 16))
+#define LFS2_DISK_VERSION_MINOR (0xffff & (LFS2_DISK_VERSION >>  0))
+
+
+/// Definitions ///
+
+// Type definitions
+typedef uint32_t lfs2_size_t;
+typedef uint32_t lfs2_off_t;
+
+typedef int32_t  lfs2_ssize_t;
+typedef int32_t  lfs2_soff_t;
+
+typedef uint32_t lfs2_block_t;
+
+// Maximum name size in bytes, may be redefined to reduce the size of the
+// info struct. Limited to <= 1022. Stored in superblock and must be
+// respected by other littlefs drivers.
+#ifndef LFS2_NAME_MAX
+#define LFS2_NAME_MAX 255
+#endif
+
+// Maximum size of a file in bytes, may be redefined to limit to support other
+// drivers. Limited on disk to <= 4294967296. However, above 2147483647 the
+// functions lfs2_file_seek, lfs2_file_size, and lfs2_file_tell will return
+// incorrect values due to using signed integers. Stored in superblock and
+// must be respected by other littlefs drivers.
+#ifndef LFS2_FILE_MAX
+#define LFS2_FILE_MAX 2147483647
+#endif
+
+// Maximum size of custom attributes in bytes, may be redefined, but there is
+// no real benefit to using a smaller LFS2_ATTR_MAX. Limited to <= 1022.
+#ifndef LFS2_ATTR_MAX
+#define LFS2_ATTR_MAX 1022
+#endif
+
+// Possible error codes, these are negative to allow
+// valid positive return values
+enum lfs2_error {
+    LFS2_ERR_OK          = 0,    // No error
+    LFS2_ERR_IO          = -5,   // Error during device operation
+    LFS2_ERR_CORRUPT     = -84,  // Corrupted
+    LFS2_ERR_NOENT       = -2,   // No directory entry
+    LFS2_ERR_EXIST       = -17,  // Entry already exists
+    LFS2_ERR_NOTDIR      = -20,  // Entry is not a dir
+    LFS2_ERR_ISDIR       = -21,  // Entry is a dir
+    LFS2_ERR_NOTEMPTY    = -39,  // Dir is not empty
+    LFS2_ERR_BADF        = -9,   // Bad file number
+    LFS2_ERR_FBIG        = -27,  // File too large
+    LFS2_ERR_INVAL       = -22,  // Invalid parameter
+    LFS2_ERR_NOSPC       = -28,  // No space left on device
+    LFS2_ERR_NOMEM       = -12,  // No more memory available
+    LFS2_ERR_NOATTR      = -61,  // No data/attr available
+    LFS2_ERR_NAMETOOLONG = -36,  // File name too long
+};
+
+// File types
+enum lfs2_type {
+    // file types
+    LFS2_TYPE_REG            = 0x001,
+    LFS2_TYPE_DIR            = 0x002,
+
+    // internally used types
+    LFS2_TYPE_SPLICE         = 0x400,
+    LFS2_TYPE_NAME           = 0x000,
+    LFS2_TYPE_STRUCT         = 0x200,
+    LFS2_TYPE_USERATTR       = 0x300,
+    LFS2_TYPE_FROM           = 0x100,
+    LFS2_TYPE_TAIL           = 0x600,
+    LFS2_TYPE_GLOBALS        = 0x700,
+    LFS2_TYPE_CRC            = 0x500,
+
+    // internally used type specializations
+    LFS2_TYPE_CREATE         = 0x401,
+    LFS2_TYPE_DELETE         = 0x4ff,
+    LFS2_TYPE_SUPERBLOCK     = 0x0ff,
+    LFS2_TYPE_DIRSTRUCT      = 0x200,
+    LFS2_TYPE_CTZSTRUCT      = 0x202,
+    LFS2_TYPE_INLINESTRUCT   = 0x201,
+    LFS2_TYPE_SOFTTAIL       = 0x600,
+    LFS2_TYPE_HARDTAIL       = 0x601,
+    LFS2_TYPE_MOVESTATE      = 0x7ff,
+
+    // internal chip sources
+    LFS2_FROM_NOOP           = 0x000,
+    LFS2_FROM_MOVE           = 0x101,
+    LFS2_FROM_USERATTRS      = 0x102,
+};
+
+// File open flags
+enum lfs2_open_flags {
+    // open flags
+    LFS2_O_RDONLY = 1,         // Open a file as read only
+    LFS2_O_WRONLY = 2,         // Open a file as write only
+    LFS2_O_RDWR   = 3,         // Open a file as read and write
+    LFS2_O_CREAT  = 0x0100,    // Create a file if it does not exist
+    LFS2_O_EXCL   = 0x0200,    // Fail if a file already exists
+    LFS2_O_TRUNC  = 0x0400,    // Truncate the existing file to zero size
+    LFS2_O_APPEND = 0x0800,    // Move to end of file on every write
+
+    // internally used flags
+    LFS2_F_DIRTY   = 0x010000, // File does not match storage
+    LFS2_F_WRITING = 0x020000, // File has been written since last flush
+    LFS2_F_READING = 0x040000, // File has been read since last flush
+    LFS2_F_ERRED   = 0x080000, // An error occured during write
+    LFS2_F_INLINE  = 0x100000, // Currently inlined in directory entry
+    LFS2_F_OPENED  = 0x200000, // File has been opened
+};
+
+// File seek flags
+enum lfs2_whence_flags {
+    LFS2_SEEK_SET = 0,   // Seek relative to an absolute position
+    LFS2_SEEK_CUR = 1,   // Seek relative to the current file position
+    LFS2_SEEK_END = 2,   // Seek relative to the end of the file
+};
+
+
+// Configuration provided during initialization of the littlefs
+struct lfs2_config {
+    // Opaque user provided context that can be used to pass
+    // information to the block device operations
+    void *context;
+
+    // Read a region in a block. Negative error codes are propogated
+    // to the user.
+    int (*read)(const struct lfs2_config *c, lfs2_block_t block,
+            lfs2_off_t off, void *buffer, lfs2_size_t size);
+
+    // Program a region in a block. The block must have previously
+    // been erased. Negative error codes are propogated to the user.
+    // May return LFS2_ERR_CORRUPT if the block should be considered bad.
+    int (*prog)(const struct lfs2_config *c, lfs2_block_t block,
+            lfs2_off_t off, const void *buffer, lfs2_size_t size);
+
+    // Erase a block. A block must be erased before being programmed.
+    // The state of an erased block is undefined. Negative error codes
+    // are propogated to the user.
+    // May return LFS2_ERR_CORRUPT if the block should be considered bad.
+    int (*erase)(const struct lfs2_config *c, lfs2_block_t block);
+
+    // Sync the state of the underlying block device. Negative error codes
+    // are propogated to the user.
+    int (*sync)(const struct lfs2_config *c);
+
+    // Minimum size of a block read. All read operations will be a
+    // multiple of this value.
+    lfs2_size_t read_size;
+
+    // Minimum size of a block program. All program operations will be a
+    // multiple of this value.
+    lfs2_size_t prog_size;
+
+    // Size of an erasable block. This does not impact ram consumption and
+    // may be larger than the physical erase size. However, non-inlined files
+    // take up at minimum one block. Must be a multiple of the read
+    // and program sizes.
+    lfs2_size_t block_size;
+
+    // Number of erasable blocks on the device.
+    lfs2_size_t block_count;
+
+    // Number of erase cycles before littlefs evicts metadata logs and moves 
+    // the metadata to another block. Suggested values are in the
+    // range 100-1000, with large values having better performance at the cost
+    // of less consistent wear distribution.
+    //
+    // Set to -1 to disable block-level wear-leveling.
+    int32_t block_cycles;
+
+    // Size of block caches. Each cache buffers a portion of a block in RAM.
+    // The littlefs needs a read cache, a program cache, and one additional
+    // cache per file. Larger caches can improve performance by storing more
+    // data and reducing the number of disk accesses. Must be a multiple of
+    // the read and program sizes, and a factor of the block size.
+    lfs2_size_t cache_size;
+
+    // Size of the lookahead buffer in bytes. A larger lookahead buffer
+    // increases the number of blocks found during an allocation pass. The
+    // lookahead buffer is stored as a compact bitmap, so each byte of RAM
+    // can track 8 blocks. Must be a multiple of 8.
+    lfs2_size_t lookahead_size;
+
+    // Optional statically allocated read buffer. Must be cache_size.
+    // By default lfs2_malloc is used to allocate this buffer.
+    void *read_buffer;
+
+    // Optional statically allocated program buffer. Must be cache_size.
+    // By default lfs2_malloc is used to allocate this buffer.
+    void *prog_buffer;
+
+    // Optional statically allocated lookahead buffer. Must be lookahead_size
+    // and aligned to a 32-bit boundary. By default lfs2_malloc is used to
+    // allocate this buffer.
+    void *lookahead_buffer;
+
+    // Optional upper limit on length of file names in bytes. No downside for
+    // larger names except the size of the info struct which is controlled by
+    // the LFS2_NAME_MAX define. Defaults to LFS2_NAME_MAX when zero. Stored in
+    // superblock and must be respected by other littlefs drivers.
+    lfs2_size_t name_max;
+
+    // Optional upper limit on files in bytes. No downside for larger files
+    // but must be <= LFS2_FILE_MAX. Defaults to LFS2_FILE_MAX when zero. Stored
+    // in superblock and must be respected by other littlefs drivers.
+    lfs2_size_t file_max;
+
+    // Optional upper limit on custom attributes in bytes. No downside for
+    // larger attributes size but must be <= LFS2_ATTR_MAX. Defaults to
+    // LFS2_ATTR_MAX when zero.
+    lfs2_size_t attr_max;
+};
+
+// File info structure
+struct lfs2_info {
+    // Type of the file, either LFS2_TYPE_REG or LFS2_TYPE_DIR
+    uint8_t type;
+
+    // Size of the file, only valid for REG files. Limited to 32-bits.
+    lfs2_size_t size;
+
+    // Name of the file stored as a null-terminated string. Limited to
+    // LFS2_NAME_MAX+1, which can be changed by redefining LFS2_NAME_MAX to
+    // reduce RAM. LFS2_NAME_MAX is stored in superblock and must be
+    // respected by other littlefs drivers.
+    char name[LFS2_NAME_MAX+1];
+};
+
+// Custom attribute structure, used to describe custom attributes
+// committed atomically during file writes.
+struct lfs2_attr {
+    // 8-bit type of attribute, provided by user and used to
+    // identify the attribute
+    uint8_t type;
+
+    // Pointer to buffer containing the attribute
+    void *buffer;
+
+    // Size of attribute in bytes, limited to LFS2_ATTR_MAX
+    lfs2_size_t size;
+};
+
+// Optional configuration provided during lfs2_file_opencfg
+struct lfs2_file_config {
+    // Optional statically allocated file buffer. Must be cache_size.
+    // By default lfs2_malloc is used to allocate this buffer.
+    void *buffer;
+
+    // Optional list of custom attributes related to the file. If the file
+    // is opened with read access, these attributes will be read from disk
+    // during the open call. If the file is opened with write access, the
+    // attributes will be written to disk every file sync or close. This
+    // write occurs atomically with update to the file's contents.
+    //
+    // Custom attributes are uniquely identified by an 8-bit type and limited
+    // to LFS2_ATTR_MAX bytes. When read, if the stored attribute is smaller
+    // than the buffer, it will be padded with zeros. If the stored attribute
+    // is larger, then it will be silently truncated. If the attribute is not
+    // found, it will be created implicitly.
+    struct lfs2_attr *attrs;
+
+    // Number of custom attributes in the list
+    lfs2_size_t attr_count;
+};
+
+
+/// internal littlefs data structures ///
+typedef struct lfs2_cache {
+    lfs2_block_t block;
+    lfs2_off_t off;
+    lfs2_size_t size;
+    uint8_t *buffer;
+} lfs2_cache_t;
+
+typedef struct lfs2_mdir {
+    lfs2_block_t pair[2];
+    uint32_t rev;
+    lfs2_off_t off;
+    uint32_t etag;
+    uint16_t count;
+    bool erased;
+    bool split;
+    lfs2_block_t tail[2];
+} lfs2_mdir_t;
+
+// littlefs directory type
+typedef struct lfs2_dir {
+    struct lfs2_dir *next;
+    uint16_t id;
+    uint8_t type;
+    lfs2_mdir_t m;
+
+    lfs2_off_t pos;
+    lfs2_block_t head[2];
+} lfs2_dir_t;
+
+// littlefs file type
+typedef struct lfs2_file {
+    struct lfs2_file *next;
+    uint16_t id;
+    uint8_t type;
+    lfs2_mdir_t m;
+
+    struct lfs2_ctz {
+        lfs2_block_t head;
+        lfs2_size_t size;
+    } ctz;
+
+    uint32_t flags;
+    lfs2_off_t pos;
+    lfs2_block_t block;
+    lfs2_off_t off;
+    lfs2_cache_t cache;
+
+    const struct lfs2_file_config *cfg;
+} lfs2_file_t;
+
+typedef struct lfs2_superblock {
+    uint32_t version;
+    lfs2_size_t block_size;
+    lfs2_size_t block_count;
+    lfs2_size_t name_max;
+    lfs2_size_t file_max;
+    lfs2_size_t attr_max;
+} lfs2_superblock_t;
+
+// The littlefs filesystem type
+typedef struct lfs2 {
+    lfs2_cache_t rcache;
+    lfs2_cache_t pcache;
+
+    lfs2_block_t root[2];
+    struct lfs2_mlist {
+        struct lfs2_mlist *next;
+        uint16_t id;
+        uint8_t type;
+        lfs2_mdir_t m;
+    } *mlist;
+    uint32_t seed;
+
+    struct lfs2_gstate {
+        uint32_t tag;
+        lfs2_block_t pair[2];
+    } gstate, gpending, gdelta;
+
+    struct lfs2_free {
+        lfs2_block_t off;
+        lfs2_block_t size;
+        lfs2_block_t i;
+        lfs2_block_t ack;
+        uint32_t *buffer;
+    } free;
+
+    const struct lfs2_config *cfg;
+    lfs2_size_t name_max;
+    lfs2_size_t file_max;
+    lfs2_size_t attr_max;
+
+#ifdef LFS2_MIGRATE
+    struct lfs21 *lfs21;
+#endif
+} lfs2_t;
+
+
+/// Filesystem functions ///
+
+// Format a block device with the littlefs
+//
+// Requires a littlefs object and config struct. This clobbers the littlefs
+// object, and does not leave the filesystem mounted. The config struct must
+// be zeroed for defaults and backwards compatibility.
+//
+// Returns a negative error code on failure.
+int lfs2_format(lfs2_t *lfs2, const struct lfs2_config *config);
+
+// Mounts a littlefs
+//
+// Requires a littlefs object and config struct. Multiple filesystems
+// may be mounted simultaneously with multiple littlefs objects. Both
+// lfs2 and config must be allocated while mounted. The config struct must
+// be zeroed for defaults and backwards compatibility.
+//
+// Returns a negative error code on failure.
+int lfs2_mount(lfs2_t *lfs2, const struct lfs2_config *config);
+
+// Unmounts a littlefs
+//
+// Does nothing besides releasing any allocated resources.
+// Returns a negative error code on failure.
+int lfs2_unmount(lfs2_t *lfs2);
+
+/// General operations ///
+
+// Removes a file or directory
+//
+// If removing a directory, the directory must be empty.
+// Returns a negative error code on failure.
+int lfs2_remove(lfs2_t *lfs2, const char *path);
+
+// Rename or move a file or directory
+//
+// If the destination exists, it must match the source in type.
+// If the destination is a directory, the directory must be empty.
+//
+// Returns a negative error code on failure.
+int lfs2_rename(lfs2_t *lfs2, const char *oldpath, const char *newpath);
+
+// Find info about a file or directory
+//
+// Fills out the info structure, based on the specified file or directory.
+// Returns a negative error code on failure.
+int lfs2_stat(lfs2_t *lfs2, const char *path, struct lfs2_info *info);
+
+// Get a custom attribute
+//
+// Custom attributes are uniquely identified by an 8-bit type and limited
+// to LFS2_ATTR_MAX bytes. When read, if the stored attribute is smaller than
+// the buffer, it will be padded with zeros. If the stored attribute is larger,
+// then it will be silently truncated. If no attribute is found, the error
+// LFS2_ERR_NOATTR is returned and the buffer is filled with zeros.
+//
+// Returns the size of the attribute, or a negative error code on failure.
+// Note, the returned size is the size of the attribute on disk, irrespective
+// of the size of the buffer. This can be used to dynamically allocate a buffer
+// or check for existance.
+lfs2_ssize_t lfs2_getattr(lfs2_t *lfs2, const char *path,
+        uint8_t type, void *buffer, lfs2_size_t size);
+
+// Set custom attributes
+//
+// Custom attributes are uniquely identified by an 8-bit type and limited
+// to LFS2_ATTR_MAX bytes. If an attribute is not found, it will be
+// implicitly created.
+//
+// Returns a negative error code on failure.
+int lfs2_setattr(lfs2_t *lfs2, const char *path,
+        uint8_t type, const void *buffer, lfs2_size_t size);
+
+// Removes a custom attribute
+//
+// If an attribute is not found, nothing happens.
+//
+// Returns a negative error code on failure.
+int lfs2_removeattr(lfs2_t *lfs2, const char *path, uint8_t type);
+
+
+/// File operations ///
+
+// Open a file
+//
+// The mode that the file is opened in is determined by the flags, which
+// are values from the enum lfs2_open_flags that are bitwise-ored together.
+//
+// Returns a negative error code on failure.
+int lfs2_file_open(lfs2_t *lfs2, lfs2_file_t *file,
+        const char *path, int flags);
+
+// Open a file with extra configuration
+//
+// The mode that the file is opened in is determined by the flags, which
+// are values from the enum lfs2_open_flags that are bitwise-ored together.
+//
+// The config struct provides additional config options per file as described
+// above. The config struct must be allocated while the file is open, and the
+// config struct must be zeroed for defaults and backwards compatibility.
+//
+// Returns a negative error code on failure.
+int lfs2_file_opencfg(lfs2_t *lfs2, lfs2_file_t *file,
+        const char *path, int flags,
+        const struct lfs2_file_config *config);
+
+// Close a file
+//
+// Any pending writes are written out to storage as though
+// sync had been called and releases any allocated resources.
+//
+// Returns a negative error code on failure.
+int lfs2_file_close(lfs2_t *lfs2, lfs2_file_t *file);
+
+// Synchronize a file on storage
+//
+// Any pending writes are written out to storage.
+// Returns a negative error code on failure.
+int lfs2_file_sync(lfs2_t *lfs2, lfs2_file_t *file);
+
+// Read data from file
+//
+// Takes a buffer and size indicating where to store the read data.
+// Returns the number of bytes read, or a negative error code on failure.
+lfs2_ssize_t lfs2_file_read(lfs2_t *lfs2, lfs2_file_t *file,
+        void *buffer, lfs2_size_t size);
+
+// Write data to file
+//
+// Takes a buffer and size indicating the data to write. The file will not
+// actually be updated on the storage until either sync or close is called.
+//
+// Returns the number of bytes written, or a negative error code on failure.
+lfs2_ssize_t lfs2_file_write(lfs2_t *lfs2, lfs2_file_t *file,
+        const void *buffer, lfs2_size_t size);
+
+// Change the position of the file
+//
+// The change in position is determined by the offset and whence flag.
+// Returns the new position of the file, or a negative error code on failure.
+lfs2_soff_t lfs2_file_seek(lfs2_t *lfs2, lfs2_file_t *file,
+        lfs2_soff_t off, int whence);
+
+// Truncates the size of the file to the specified size
+//
+// Returns a negative error code on failure.
+int lfs2_file_truncate(lfs2_t *lfs2, lfs2_file_t *file, lfs2_off_t size);
+
+// Return the position of the file
+//
+// Equivalent to lfs2_file_seek(lfs2, file, 0, LFS2_SEEK_CUR)
+// Returns the position of the file, or a negative error code on failure.
+lfs2_soff_t lfs2_file_tell(lfs2_t *lfs2, lfs2_file_t *file);
+
+// Change the position of the file to the beginning of the file
+//
+// Equivalent to lfs2_file_seek(lfs2, file, 0, LFS2_SEEK_SET)
+// Returns a negative error code on failure.
+int lfs2_file_rewind(lfs2_t *lfs2, lfs2_file_t *file);
+
+// Return the size of the file
+//
+// Similar to lfs2_file_seek(lfs2, file, 0, LFS2_SEEK_END)
+// Returns the size of the file, or a negative error code on failure.
+lfs2_soff_t lfs2_file_size(lfs2_t *lfs2, lfs2_file_t *file);
+
+
+/// Directory operations ///
+
+// Create a directory
+//
+// Returns a negative error code on failure.
+int lfs2_mkdir(lfs2_t *lfs2, const char *path);
+
+// Open a directory
+//
+// Once open a directory can be used with read to iterate over files.
+// Returns a negative error code on failure.
+int lfs2_dir_open(lfs2_t *lfs2, lfs2_dir_t *dir, const char *path);
+
+// Close a directory
+//
+// Releases any allocated resources.
+// Returns a negative error code on failure.
+int lfs2_dir_close(lfs2_t *lfs2, lfs2_dir_t *dir);
+
+// Read an entry in the directory
+//
+// Fills out the info structure, based on the specified file or directory.
+// Returns a positive value on success, 0 at the end of directory,
+// or a negative error code on failure.
+int lfs2_dir_read(lfs2_t *lfs2, lfs2_dir_t *dir, struct lfs2_info *info);
+
+// Change the position of the directory
+//
+// The new off must be a value previous returned from tell and specifies
+// an absolute offset in the directory seek.
+//
+// Returns a negative error code on failure.
+int lfs2_dir_seek(lfs2_t *lfs2, lfs2_dir_t *dir, lfs2_off_t off);
+
+// Return the position of the directory
+//
+// The returned offset is only meant to be consumed by seek and may not make
+// sense, but does indicate the current position in the directory iteration.
+//
+// Returns the position of the directory, or a negative error code on failure.
+lfs2_soff_t lfs2_dir_tell(lfs2_t *lfs2, lfs2_dir_t *dir);
+
+// Change the position of the directory to the beginning of the directory
+//
+// Returns a negative error code on failure.
+int lfs2_dir_rewind(lfs2_t *lfs2, lfs2_dir_t *dir);
+
+
+/// Filesystem-level filesystem operations
+
+// Finds the current size of the filesystem
+//
+// Note: Result is best effort. If files share COW structures, the returned
+// size may be larger than the filesystem actually is.
+//
+// Returns the number of allocated blocks, or a negative error code on failure.
+lfs2_ssize_t lfs2_fs_size(lfs2_t *lfs2);
+
+// Traverse through all blocks in use by the filesystem
+//
+// The provided callback will be called with each block address that is
+// currently in use by the filesystem. This can be used to determine which
+// blocks are in use or how much of the storage is available.
+//
+// Returns a negative error code on failure.
+int lfs2_fs_traverse(lfs2_t *lfs2, int (*cb)(void*, lfs2_block_t), void *data);
+
+#ifdef LFS2_MIGRATE
+// Attempts to migrate a previous version of littlefs
+//
+// Behaves similarly to the lfs2_format function. Attempts to mount
+// the previous version of littlefs and update the filesystem so it can be
+// mounted with the current version of littlefs.
+//
+// Requires a littlefs object and config struct. This clobbers the littlefs
+// object, and does not leave the filesystem mounted. The config struct must
+// be zeroed for defaults and backwards compatibility.
+//
+// Returns a negative error code on failure.
+int lfs2_migrate(lfs2_t *lfs2, const struct lfs2_config *cfg);
+#endif
+
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif
diff --git a/lib/littlefs/lfs2_util.c b/lib/littlefs/lfs2_util.c
new file mode 100644
index 0000000000..083a99c36c
--- /dev/null
+++ b/lib/littlefs/lfs2_util.c
@@ -0,0 +1,33 @@
+/*
+ * lfs2 util functions
+ *
+ * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#include "lfs2_util.h"
+
+// Only compile if user does not provide custom config
+#ifndef LFS2_CONFIG
+
+
+// Software CRC implementation with small lookup table
+uint32_t lfs2_crc(uint32_t crc, const void *buffer, size_t size) {
+    static const uint32_t rtable[16] = {
+        0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
+        0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
+        0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
+        0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c,
+    };
+
+    const uint8_t *data = buffer;
+
+    for (size_t i = 0; i < size; i++) {
+        crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 0)) & 0xf];
+        crc = (crc >> 4) ^ rtable[(crc ^ (data[i] >> 4)) & 0xf];
+    }
+
+    return crc;
+}
+
+
+#endif
diff --git a/lib/littlefs/lfs2_util.h b/lib/littlefs/lfs2_util.h
new file mode 100644
index 0000000000..0f27073693
--- /dev/null
+++ b/lib/littlefs/lfs2_util.h
@@ -0,0 +1,230 @@
+/*
+ * lfs2 utility functions
+ *
+ * Copyright (c) 2017, Arm Limited. All rights reserved.
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#ifndef LFS2_UTIL_H
+#define LFS2_UTIL_H
+
+// Users can override lfs2_util.h with their own configuration by defining
+// LFS2_CONFIG as a header file to include (-DLFS2_CONFIG=lfs2_config.h).
+//
+// If LFS2_CONFIG is used, none of the default utils will be emitted and must be
+// provided by the config file. To start, I would suggest copying lfs2_util.h
+// and modifying as needed.
+#ifdef LFS2_CONFIG
+#define LFS2_STRINGIZE(x) LFS2_STRINGIZE2(x)
+#define LFS2_STRINGIZE2(x) #x
+#include LFS2_STRINGIZE(LFS2_CONFIG)
+#else
+
+// System includes
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+#include <inttypes.h>
+
+#ifndef LFS2_NO_MALLOC
+#include <stdlib.h>
+#endif
+#ifndef LFS2_NO_ASSERT
+#include <assert.h>
+#endif
+#if !defined(LFS2_NO_DEBUG) || \
+        !defined(LFS2_NO_WARN) || \
+        !defined(LFS2_NO_ERROR) || \
+        defined(LFS2_YES_TRACE)
+#include <stdio.h>
+#endif
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+
+// Macros, may be replaced by system specific wrappers. Arguments to these
+// macros must not have side-effects as the macros can be removed for a smaller
+// code footprint
+
+// Logging functions
+#ifdef LFS2_YES_TRACE
+#define LFS2_TRACE(fmt, ...) \
+    printf("lfs2_trace:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS2_TRACE(fmt, ...)
+#endif
+
+#ifndef LFS2_NO_DEBUG
+#define LFS2_DEBUG(fmt, ...) \
+    printf("lfs2_debug:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS2_DEBUG(fmt, ...)
+#endif
+
+#ifndef LFS2_NO_WARN
+#define LFS2_WARN(fmt, ...) \
+    printf("lfs2_warn:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS2_WARN(fmt, ...)
+#endif
+
+#ifndef LFS2_NO_ERROR
+#define LFS2_ERROR(fmt, ...) \
+    printf("lfs2_error:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS2_ERROR(fmt, ...)
+#endif
+
+// Runtime assertions
+#ifndef LFS2_NO_ASSERT
+#define LFS2_ASSERT(test) assert(test)
+#else
+#define LFS2_ASSERT(test)
+#endif
+
+
+// Builtin functions, these may be replaced by more efficient
+// toolchain-specific implementations. LFS2_NO_INTRINSICS falls back to a more
+// expensive basic C implementation for debugging purposes
+
+// Min/max functions for unsigned 32-bit numbers
+static inline uint32_t lfs2_max(uint32_t a, uint32_t b) {
+    return (a > b) ? a : b;
+}
+
+static inline uint32_t lfs2_min(uint32_t a, uint32_t b) {
+    return (a < b) ? a : b;
+}
+
+// Align to nearest multiple of a size
+static inline uint32_t lfs2_aligndown(uint32_t a, uint32_t alignment) {
+    return a - (a % alignment);
+}
+
+static inline uint32_t lfs2_alignup(uint32_t a, uint32_t alignment) {
+    return lfs2_aligndown(a + alignment-1, alignment);
+}
+
+// Find the next smallest power of 2 less than or equal to a
+static inline uint32_t lfs2_npw2(uint32_t a) {
+#if !defined(LFS2_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
+    return 32 - __builtin_clz(a-1);
+#else
+    uint32_t r = 0;
+    uint32_t s;
+    a -= 1;
+    s = (a > 0xffff) << 4; a >>= s; r |= s;
+    s = (a > 0xff  ) << 3; a >>= s; r |= s;
+    s = (a > 0xf   ) << 2; a >>= s; r |= s;
+    s = (a > 0x3   ) << 1; a >>= s; r |= s;
+    return (r | (a >> 1)) + 1;
+#endif
+}
+
+// Count the number of trailing binary zeros in a
+// lfs2_ctz(0) may be undefined
+static inline uint32_t lfs2_ctz(uint32_t a) {
+#if !defined(LFS2_NO_INTRINSICS) && defined(__GNUC__)
+    return __builtin_ctz(a);
+#else
+    return lfs2_npw2((a & -a) + 1) - 1;
+#endif
+}
+
+// Count the number of binary ones in a
+static inline uint32_t lfs2_popc(uint32_t a) {
+#if !defined(LFS2_NO_INTRINSICS) && (defined(__GNUC__) || defined(__CC_ARM))
+    return __builtin_popcount(a);
+#else
+    a = a - ((a >> 1) & 0x55555555);
+    a = (a & 0x33333333) + ((a >> 2) & 0x33333333);
+    return (((a + (a >> 4)) & 0xf0f0f0f) * 0x1010101) >> 24;
+#endif
+}
+
+// Find the sequence comparison of a and b, this is the distance
+// between a and b ignoring overflow
+static inline int lfs2_scmp(uint32_t a, uint32_t b) {
+    return (int)(unsigned)(a - b);
+}
+
+// Convert between 32-bit little-endian and native order
+static inline uint32_t lfs2_fromle32(uint32_t a) {
+#if !defined(LFS2_NO_INTRINSICS) && ( \
+    (defined(  BYTE_ORDER  ) && defined(  ORDER_LITTLE_ENDIAN  ) &&   BYTE_ORDER   ==   ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && defined(__ORDER_LITTLE_ENDIAN  ) && __BYTE_ORDER   == __ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__))
+    return a;
+#elif !defined(LFS2_NO_INTRINSICS) && ( \
+    (defined(  BYTE_ORDER  ) && defined(  ORDER_BIG_ENDIAN  ) &&   BYTE_ORDER   ==   ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && defined(__ORDER_BIG_ENDIAN  ) && __BYTE_ORDER   == __ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__))
+    return __builtin_bswap32(a);
+#else
+    return (((uint8_t*)&a)[0] <<  0) |
+           (((uint8_t*)&a)[1] <<  8) |
+           (((uint8_t*)&a)[2] << 16) |
+           (((uint8_t*)&a)[3] << 24);
+#endif
+}
+
+static inline uint32_t lfs2_tole32(uint32_t a) {
+    return lfs2_fromle32(a);
+}
+
+// Convert between 32-bit big-endian and native order
+static inline uint32_t lfs2_frombe32(uint32_t a) {
+#if !defined(LFS2_NO_INTRINSICS) && ( \
+    (defined(  BYTE_ORDER  ) && defined(  ORDER_LITTLE_ENDIAN  ) &&   BYTE_ORDER   ==   ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && defined(__ORDER_LITTLE_ENDIAN  ) && __BYTE_ORDER   == __ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__))
+    return __builtin_bswap32(a);
+#elif !defined(LFS2_NO_INTRINSICS) && ( \
+    (defined(  BYTE_ORDER  ) && defined(  ORDER_BIG_ENDIAN  ) &&   BYTE_ORDER   ==   ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && defined(__ORDER_BIG_ENDIAN  ) && __BYTE_ORDER   == __ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__))
+    return a;
+#else
+    return (((uint8_t*)&a)[0] << 24) |
+           (((uint8_t*)&a)[1] << 16) |
+           (((uint8_t*)&a)[2] <<  8) |
+           (((uint8_t*)&a)[3] <<  0);
+#endif
+}
+
+static inline uint32_t lfs2_tobe32(uint32_t a) {
+    return lfs2_frombe32(a);
+}
+
+// Calculate CRC-32 with polynomial = 0x04c11db7
+uint32_t lfs2_crc(uint32_t crc, const void *buffer, size_t size);
+
+// Allocate memory, only used if buffers are not provided to littlefs
+// Note, memory must be 64-bit aligned
+static inline void *lfs2_malloc(size_t size) {
+#ifndef LFS2_NO_MALLOC
+    return malloc(size);
+#else
+    (void)size;
+    return NULL;
+#endif
+}
+
+// Deallocate memory, only used if buffers are not provided to littlefs
+static inline void lfs2_free(void *p) {
+#ifndef LFS2_NO_MALLOC
+    free(p);
+#else
+    (void)p;
+#endif
+}
+
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif
+#endif