extmod: Add generic VFS sub-system.

This provides mp_vfs_XXX functions (eg mount, open, listdir) which are
agnostic to the underlying filesystem type, and just require an object with
the relevant filesystem-like methods (eg .mount, .open, .listidr) which can
then be mounted.

These mp_vfs_XXX functions would typically be used by a port to implement
the "uos" module, and mp_vfs_open would be the builtin open function.

This feature is controlled by MICROPY_VFS, disabled by default.

9 files changed, 492 insertions, 1 deletions

diff --git a/extmod/vfs.c b/extmod/vfs.c
new file mode 100644
index 0000000000..2880271c6d
--- /dev/null
+++ b/extmod/vfs.c
@@ -0,0 +1,310 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include "py/runtime.h"
+#include "py/objstr.h"
+#include "py/mperrno.h"
+#include "extmod/vfs.h"
+
+#if MICROPY_VFS
+
+// ROOT is 0 so that the default current directory is the root directory
+#define VFS_NONE ((vfs_mount_t*)1)
+#define VFS_ROOT ((vfs_mount_t*)0)
+
+typedef struct _vfs_mount_t {
+    const char *str; // mount point with leading /
+    size_t len;
+    mp_obj_t obj;
+    struct _vfs_mount_t *next;
+} vfs_mount_t;
+
+// path is the path to lookup and *path_out holds the path within the VFS
+// object (starts with / if an absolute path).
+// Returns VFS_ROOT for root dir (and then path_out is undefined) and VFS_NONE
+// for path not found.
+STATIC vfs_mount_t *lookup_path_raw(const char *path, const char **path_out) {
+    if (path[0] == '/' && path[1] == 0) {
+        return VFS_ROOT;
+    } else if (MP_STATE_VM(vfs_cur) == VFS_ROOT) {
+        // in root dir
+        if (path[0] == 0) {
+            return VFS_ROOT;
+        }
+    } else if (*path != '/') {
+        // a relative path within a mounted device
+        *path_out = path;
+        return MP_STATE_VM(vfs_cur);
+    }
+
+    for (vfs_mount_t *vfs = MP_STATE_VM(vfs_mount_table); vfs != NULL; vfs = vfs->next) {
+        if (strncmp(path, vfs->str, vfs->len) == 0) {
+            if (path[vfs->len] == '/') {
+                *path_out = path + vfs->len;
+                return vfs;
+            } else if (path[vfs->len] == '\0') {
+                *path_out = "/";
+                return vfs;
+            }
+        }
+    }
+
+    // mount point not found
+    return VFS_NONE;
+}
+
+// Version of lookup_path_raw that takes and returns uPy string objects.
+STATIC vfs_mount_t *lookup_path(mp_obj_t path_in, mp_obj_t *path_out) {
+    const char *path = mp_obj_str_get_str(path_in);
+    const char *p_out;
+    vfs_mount_t *vfs = lookup_path_raw(path, &p_out);
+    if (vfs != VFS_NONE && vfs != VFS_ROOT) {
+        *path_out = mp_obj_new_str_of_type(mp_obj_get_type(path_in),
+            (const byte*)p_out, strlen(p_out));
+    }
+    return vfs;
+}
+
+STATIC mp_obj_t mp_vfs_proxy_call(vfs_mount_t *vfs, qstr meth_name, size_t n_args, const mp_obj_t *args) {
+    if (vfs == VFS_NONE) {
+        // mount point not found
+        mp_raise_OSError(MP_ENODEV);
+    }
+    if (vfs == VFS_ROOT) {
+        // can't do operation on root dir
+        mp_raise_OSError(MP_EPERM);
+    }
+    mp_obj_t meth[n_args + 2];
+    mp_load_method(vfs->obj, meth_name, meth);
+    if (args != NULL) {
+        memcpy(meth + 2, args, n_args * sizeof(*args));
+    }
+    return mp_call_method_n_kw(n_args, 0, meth);
+}
+
+mp_import_stat_t mp_vfs_import_stat(const char *path) {
+    const char *path_out;
+    vfs_mount_t *vfs = lookup_path_raw(path, &path_out);
+    if (vfs == VFS_NONE || vfs == VFS_ROOT) {
+        return MP_IMPORT_STAT_NO_EXIST;
+    }
+    // TODO delegate to vfs.stat() method
+    return MP_IMPORT_STAT_NO_EXIST;
+}
+
+mp_obj_t mp_vfs_mount(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_readonly, ARG_mkfs };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_readonly, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_false} },
+        { MP_QSTR_mkfs, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_obj = mp_const_false} },
+    };
+
+    // parse args
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args - 2, pos_args + 2, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    // get the mount point
+    mp_uint_t mnt_len;
+    const char *mnt_str = mp_obj_str_get_data(pos_args[1], &mnt_len);
+
+    // create new object
+    vfs_mount_t *vfs = m_new_obj(vfs_mount_t);
+    vfs->str = mnt_str;
+    vfs->len = mnt_len;
+    vfs->obj = pos_args[0];
+    vfs->next = NULL;
+
+    // call the underlying object to do any mounting operation
+    mp_vfs_proxy_call(vfs, MP_QSTR_mount, 2, (mp_obj_t*)&args);
+
+    // check that the destination mount point is unused
+    const char *path_out;
+    if (lookup_path_raw(mp_obj_str_get_str(pos_args[1]), &path_out) != VFS_NONE) {
+        mp_raise_OSError(MP_EPERM);
+    }
+
+    // insert the vfs into the mount table
+    vfs_mount_t **vfsp = &MP_STATE_VM(vfs_mount_table);
+    while (*vfsp != NULL) {
+        vfsp = &(*vfsp)->next;
+    }
+    *vfsp = vfs;
+
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(mp_vfs_mount_obj, 2, mp_vfs_mount);
+
+mp_obj_t mp_vfs_umount(mp_obj_t mnt_in) {
+    // remove vfs from the mount table
+    vfs_mount_t *vfs = NULL;
+    mp_uint_t mnt_len;
+    const char *mnt_str = NULL;
+    if (MP_OBJ_IS_STR(mnt_in)) {
+        mnt_str = mp_obj_str_get_data(mnt_in, &mnt_len);
+    }
+    for (vfs_mount_t **vfsp = &MP_STATE_VM(vfs_mount_table); *vfsp != NULL; vfsp = &(*vfsp)->next) {
+        if ((mnt_str != NULL && !memcmp(mnt_str, (*vfsp)->str, mnt_len + 1)) || (*vfsp)->obj == mnt_in) {
+            vfs = *vfsp;
+            *vfsp = (*vfsp)->next;
+            break;
+        }
+    }
+
+    if (vfs == NULL) {
+        mp_raise_OSError(MP_EINVAL);
+    }
+
+    // if we unmounted the current device then set current to root
+    if (MP_STATE_VM(vfs_cur) == vfs) {
+        MP_STATE_VM(vfs_cur) = VFS_ROOT;
+    }
+
+    // call the underlying object to do any unmounting operation
+    mp_vfs_proxy_call(vfs, MP_QSTR_umount, 0, NULL);
+
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_umount_obj, mp_vfs_umount);
+
+mp_obj_t mp_vfs_open(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
+    enum { ARG_file, ARG_mode, ARG_encoding };
+    static const mp_arg_t allowed_args[] = {
+        { MP_QSTR_file, MP_ARG_OBJ | MP_ARG_REQUIRED, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} },
+        { MP_QSTR_mode, MP_ARG_OBJ, {.u_rom_obj = MP_ROM_QSTR(MP_QSTR_r)} },
+    };
+
+    // parse args
+    mp_arg_val_t args[MP_ARRAY_SIZE(allowed_args)];
+    mp_arg_parse_all(n_args, pos_args, kw_args, MP_ARRAY_SIZE(allowed_args), allowed_args, args);
+
+    vfs_mount_t *vfs = lookup_path((mp_obj_t)args[ARG_file].u_rom_obj, &args[ARG_file].u_obj);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_open, 2, (mp_obj_t*)&args);
+}
+MP_DEFINE_CONST_FUN_OBJ_KW(mp_vfs_open_obj, 0, mp_vfs_open);
+
+mp_obj_t mp_vfs_chdir(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    if (vfs != VFS_ROOT) {
+        mp_vfs_proxy_call(vfs, MP_QSTR_chdir, 1, &path_out);
+    }
+    MP_STATE_VM(vfs_cur) = vfs;
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_chdir_obj, mp_vfs_chdir);
+
+mp_obj_t mp_vfs_getcwd(void) {
+    if (MP_STATE_VM(vfs_cur) == VFS_ROOT) {
+        return MP_OBJ_NEW_QSTR(MP_QSTR__slash_);
+    }
+    mp_obj_t cwd_o = mp_vfs_proxy_call(MP_STATE_VM(vfs_cur), MP_QSTR_getcwd, 0, NULL);
+    const char *cwd = mp_obj_str_get_str(cwd_o);
+    vstr_t vstr;
+    vstr_init(&vstr, MP_STATE_VM(vfs_cur)->len + strlen(cwd) + 1);
+    vstr_add_strn(&vstr, MP_STATE_VM(vfs_cur)->str, MP_STATE_VM(vfs_cur)->len);
+    if (!(cwd[0] == '/' && cwd[1] == 0)) {
+        vstr_add_str(&vstr, cwd);
+    }
+    return mp_obj_new_str_from_vstr(&mp_type_str, &vstr);
+}
+MP_DEFINE_CONST_FUN_OBJ_0(mp_vfs_getcwd_obj, mp_vfs_getcwd);
+
+mp_obj_t mp_vfs_listdir(size_t n_args, const mp_obj_t *args) {
+    mp_obj_t path_in;
+    if (n_args == 1) {
+        path_in = args[0];
+    } else {
+        path_in = MP_OBJ_NEW_QSTR(MP_QSTR_);
+    }
+
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+
+    if (vfs == VFS_ROOT) {
+        // list the root directory
+        mp_obj_t dir_list = mp_obj_new_list(0, NULL);
+        for (vfs = MP_STATE_VM(vfs_mount_table); vfs != NULL; vfs = vfs->next) {
+            mp_obj_list_append(dir_list, mp_obj_new_str_of_type(mp_obj_get_type(path_in),
+                (const byte*)vfs->str + 1, vfs->len - 1));
+        }
+        return dir_list;
+    }
+
+    return mp_vfs_proxy_call(vfs, MP_QSTR_listdir, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_vfs_listdir_obj, 0, 1, mp_vfs_listdir);
+
+mp_obj_t mp_vfs_mkdir(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_mkdir, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_mkdir_obj, mp_vfs_mkdir);
+
+mp_obj_t mp_vfs_remove(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_remove, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_remove_obj, mp_vfs_remove);
+
+mp_obj_t mp_vfs_rename(mp_obj_t old_path_in, mp_obj_t new_path_in) {
+    mp_obj_t args[2];
+    vfs_mount_t *old_vfs = lookup_path(old_path_in, &args[0]);
+    vfs_mount_t *new_vfs = lookup_path(new_path_in, &args[1]);
+    if (old_vfs != new_vfs) {
+        // can't rename across filesystems
+        mp_raise_OSError(MP_EPERM);
+    }
+    return mp_vfs_proxy_call(old_vfs, MP_QSTR_rename, 2, args);
+}
+MP_DEFINE_CONST_FUN_OBJ_2(mp_vfs_rename_obj, mp_vfs_rename);
+
+mp_obj_t mp_vfs_rmdir(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_rmdir, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_rmdir_obj, mp_vfs_rmdir);
+
+mp_obj_t mp_vfs_stat(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_stat, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_stat_obj, mp_vfs_stat);
+
+mp_obj_t mp_vfs_statvfs(mp_obj_t path_in) {
+    mp_obj_t path_out;
+    vfs_mount_t *vfs = lookup_path(path_in, &path_out);
+    return mp_vfs_proxy_call(vfs, MP_QSTR_statvfs, 1, &path_out);
+}
+MP_DEFINE_CONST_FUN_OBJ_1(mp_vfs_statvfs_obj, mp_vfs_statvfs);
+
+#endif // MICROPY_VFS
diff --git a/extmod/vfs.h b/extmod/vfs.h
new file mode 100644
index 0000000000..68f0b71548
--- /dev/null
+++ b/extmod/vfs.h
@@ -0,0 +1,60 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef MICROPY_INCLUDED_EXTMOD_VFS_H
+#define MICROPY_INCLUDED_EXTMOD_VFS_H
+
+#include "py/lexer.h"
+#include "py/obj.h"
+
+mp_import_stat_t mp_vfs_import_stat(const char *path);
+mp_obj_t mp_vfs_mount(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args);
+mp_obj_t mp_vfs_umount(mp_obj_t mnt_in);
+mp_obj_t mp_vfs_open(size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args);
+mp_obj_t mp_vfs_chdir(mp_obj_t path_in);
+mp_obj_t mp_vfs_getcwd(void);
+mp_obj_t mp_vfs_listdir(size_t n_args, const mp_obj_t *args);
+mp_obj_t mp_vfs_mkdir(mp_obj_t path_in);
+mp_obj_t mp_vfs_remove(mp_obj_t path_in);
+mp_obj_t mp_vfs_rename(mp_obj_t old_path_in, mp_obj_t new_path_in);
+mp_obj_t mp_vfs_rmdir(mp_obj_t path_in);
+mp_obj_t mp_vfs_stat(mp_obj_t path_in);
+mp_obj_t mp_vfs_statvfs(mp_obj_t path_in);
+
+MP_DECLARE_CONST_FUN_OBJ_KW(mp_vfs_mount_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_umount_obj);
+MP_DECLARE_CONST_FUN_OBJ_KW(mp_vfs_open_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_chdir_obj);
+MP_DECLARE_CONST_FUN_OBJ_0(mp_vfs_getcwd_obj);
+MP_DECLARE_CONST_FUN_OBJ_VAR_BETWEEN(mp_vfs_listdir_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_mkdir_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_remove_obj);
+MP_DECLARE_CONST_FUN_OBJ_2(mp_vfs_rename_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_rmdir_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_stat_obj);
+MP_DECLARE_CONST_FUN_OBJ_1(mp_vfs_statvfs_obj);
+
+#endif // MICROPY_INCLUDED_EXTMOD_VFS_H
diff --git a/extmod/vfs_reader.c b/extmod/vfs_reader.c
new file mode 100644
index 0000000000..718bdeeb65
--- /dev/null
+++ b/extmod/vfs_reader.c
@@ -0,0 +1,97 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2013-2017 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "py/nlr.h"
+#include "py/stream.h"
+#include "py/reader.h"
+#include "extmod/vfs.h"
+
+#if MICROPY_READER_VFS
+
+typedef struct _mp_reader_vfs_t {
+    mp_obj_t file;
+    uint16_t len;
+    uint16_t pos;
+    byte buf[24];
+} mp_reader_vfs_t;
+
+STATIC mp_uint_t mp_reader_vfs_readbyte(void *data) {
+    mp_reader_vfs_t *reader = (mp_reader_vfs_t*)data;
+    if (reader->pos >= reader->len) {
+        if (reader->len < sizeof(reader->buf)) {
+            return MP_READER_EOF;
+        } else {
+            int errcode;
+            reader->len = mp_stream_rw(reader->file, reader->buf, sizeof(reader->buf),
+                &errcode, MP_STREAM_RW_READ | MP_STREAM_RW_ONCE);
+            if (errcode != 0) {
+                // TODO handle errors properly
+                return MP_READER_EOF;
+            }
+            if (reader->len == 0) {
+                return MP_READER_EOF;
+            }
+            reader->pos = 0;
+        }
+    }
+    return reader->buf[reader->pos++];
+}
+
+STATIC void mp_reader_vfs_close(void *data) {
+    mp_reader_vfs_t *reader = (mp_reader_vfs_t*)data;
+    mp_stream_close(reader->file);
+    m_del_obj(mp_reader_vfs_t, reader);
+}
+
+int mp_reader_new_file(mp_reader_t *reader, const char *filename) {
+    mp_reader_vfs_t *rf = m_new_obj_maybe(mp_reader_vfs_t);
+    if (rf == NULL) {
+        return MP_ENOMEM;
+    }
+    // TODO we really should just let this function raise a uPy exception
+    nlr_buf_t nlr;
+    if (nlr_push(&nlr) == 0) {
+        mp_obj_t arg = mp_obj_new_str(filename, strlen(filename), false);
+        rf->file = mp_vfs_open(1, &arg, (mp_map_t*)&mp_const_empty_map);
+        int errcode;
+        rf->len = mp_stream_rw(rf->file, rf->buf, sizeof(rf->buf), &errcode, MP_STREAM_RW_READ | MP_STREAM_RW_ONCE);
+        if (errcode != 0) {
+            return errcode;
+        }
+    } else {
+        return MP_ENOENT; // assume error was "file not found"
+    }
+    rf->pos = 0;
+    reader->data = rf;
+    reader->readbyte = mp_reader_vfs_readbyte;
+    reader->close = mp_reader_vfs_close;
+    return 0; // success
+}
+
+#endif // MICROPY_READER_VFS
diff --git a/py/lexer.c b/py/lexer.c
index 458fba0900..e9b571ca40 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -753,7 +753,7 @@ mp_lexer_t *mp_lexer_new_from_str_len(qstr src_name, const char *str, mp_uint_t
     return mp_lexer_new(src_name, reader);
 }
 
-#if MICROPY_READER_POSIX || MICROPY_READER_FATFS
+#if MICROPY_READER_POSIX || MICROPY_READER_VFS || MICROPY_READER_FATFS
 
 mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
     mp_reader_t reader;
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 3bccada11d..a924eda0c6 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -398,6 +398,11 @@
 #define MICROPY_READER_POSIX (0)
 #endif
 
+// Whether to use the VFS reader for importing files
+#ifndef MICROPY_READER_VFS
+#define MICROPY_READER_VFS (0)
+#endif
+
 // Whether to use the FatFS reader for importing files
 #ifndef MICROPY_READER_FATFS
 #define MICROPY_READER_FATFS (0)
@@ -621,6 +626,11 @@ typedef double mp_float_t;
 #define MICROPY_FSUSERMOUNT (0)
 #endif
 
+// Support for generic VFS sub-system
+#ifndef MICROPY_VFS
+#define MICROPY_VFS (0)
+#endif
+
 /*****************************************************************************/
 /* Fine control over Python builtins, classes, modules, etc                  */
 
diff --git a/py/mpstate.h b/py/mpstate.h
index 91fb68b3ad..9c73f7778b 100644
--- a/py/mpstate.h
+++ b/py/mpstate.h
@@ -165,6 +165,11 @@ typedef struct _mp_state_vm_t {
     struct _fs_user_mount_t *fs_user_mount[MICROPY_FATFS_VOLUMES];
     #endif
 
+    #if MICROPY_VFS
+    struct _vfs_mount_t *vfs_cur;
+    struct _vfs_mount_t *vfs_mount_table;
+    #endif
+
     //
     // END ROOT POINTER SECTION
     ////////////////////////////////////////////////////////////
diff --git a/py/py.mk b/py/py.mk
index 69819054b7..94265c3f44 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -233,6 +233,8 @@ PY_O_BASENAME = \
 	../extmod/modwebrepl.o \
 	../extmod/modframebuf.o \
 	../extmod/fsusermount.o \
+	../extmod/vfs.o \
+	../extmod/vfs_reader.o \
 	../extmod/vfs_fat.o \
 	../extmod/vfs_fat_ffconf.o \
 	../extmod/vfs_fat_diskio.o \
diff --git a/py/qstrdefs.h b/py/qstrdefs.h
index c98a253a69..4581e5e1b1 100644
--- a/py/qstrdefs.h
+++ b/py/qstrdefs.h
@@ -36,6 +36,7 @@ QCFG(BYTES_IN_HASH, MICROPY_QSTR_BYTES_IN_HASH)
 Q()
 Q(*)
 Q(_)
+Q(/)
 Q(%#o)
 Q(%#x)
 Q({:#b})
diff --git a/py/runtime.c b/py/runtime.c
index 0ccfd8d874..e6aef21d77 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -105,6 +105,12 @@ void mp_init(void) {
     memset(MP_STATE_VM(fs_user_mount), 0, sizeof(MP_STATE_VM(fs_user_mount)));
     #endif
 
+    #if MICROPY_VFS
+    // initialise the VFS sub-system
+    MP_STATE_VM(vfs_cur) = NULL;
+    MP_STATE_VM(vfs_mount_table) = NULL;
+    #endif
+
     #if MICROPY_PY_THREAD_GIL
     mp_thread_mutex_init(&MP_STATE_VM(gil_mutex));
     #endif