extmod/vfs_lfs: Add mtime support to littlefs files.

This commit adds support for modification time of files on littlefs v2
filesystems, using file attributes.  For some background see issue #6114.

Features/properties of this implementation:
- Only supported on littlefs2 (not littlefs1).
- Uses littlefs2's general file attributes to store the timestamp.
- The timestamp is 64-bits and stores nanoseconds since 1970/1/1 (if the
  range to the year 2554 is not enough then additional bits can be added to
  this timestamp by adding another file attribute).
- mtime is enabled by default but can be disabled in the constructor, eg:
  uos.mount(uos.VfsLfs2(bdev, mtime=False), '/flash')
- It's fully backwards compatible, existing littlefs2 filesystems will work
  without reformatting and timestamps will be added transparently to
  existing files (once they are opened for writing).
- Files without timestamps will open correctly, and stat will just return 0
  for their timestamp.
- mtime can be disabled or enabled each mount time and timestamps will only
  be updated if mtime is enabled (otherwise they will be untouched).

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 98 insertions, 0 deletions

diff --git a/tests/extmod/vfs_lfs_mtime.py b/tests/extmod/vfs_lfs_mtime.py
new file mode 100644
index 0000000000..0108076884
--- /dev/null
+++ b/tests/extmod/vfs_lfs_mtime.py
@@ -0,0 +1,98 @@
+# Test for VfsLfs using a RAM device, mtime feature
+
+try:
+    import utime, uos
+
+    utime.sleep
+    uos.VfsLfs2
+except (ImportError, AttributeError):
+    print("SKIP")
+    raise SystemExit
+
+
+class RAMBlockDevice:
+    ERASE_BLOCK_SIZE = 1024
+
+    def __init__(self, blocks):
+        self.data = bytearray(blocks * self.ERASE_BLOCK_SIZE)
+
+    def readblocks(self, block, buf, off):
+        addr = block * self.ERASE_BLOCK_SIZE + off
+        for i in range(len(buf)):
+            buf[i] = self.data[addr + i]
+
+    def writeblocks(self, block, buf, off):
+        addr = block * self.ERASE_BLOCK_SIZE + off
+        for i in range(len(buf)):
+            self.data[addr + i] = buf[i]
+
+    def ioctl(self, op, arg):
+        if op == 4:  # block count
+            return len(self.data) // self.ERASE_BLOCK_SIZE
+        if op == 5:  # block size
+            return self.ERASE_BLOCK_SIZE
+        if op == 6:  # erase block
+            return 0
+
+
+def test(bdev, vfs_class):
+    print("test", vfs_class)
+
+    # Initial format of block device.
+    vfs_class.mkfs(bdev)
+
+    # construction
+    print("mtime=True")
+    vfs = vfs_class(bdev, mtime=True)
+
+    # Create an empty file, should have a timestamp.
+    vfs.open("test1", "wt").close()
+
+    # Wait 1 second so mtime will increase by at least 1.
+    utime.sleep(1)
+
+    # Create another empty file, should have a timestamp.
+    vfs.open("test2", "wt").close()
+
+    # Stat the files and check that test1 is older than test2.
+    stat1 = vfs.stat("test1")
+    stat2 = vfs.stat("test2")
+    print(stat1[8] != 0, stat2[8] != 0)
+    print(stat1[8] < stat2[8])
+
+    # Wait 1 second so mtime will increase by at least 1.
+    utime.sleep(1)
+
+    # Open test1 for reading and ensure mtime did not change.
+    vfs.open("test1", "rt").close()
+    print(vfs.stat("test1") == stat1)
+
+    # Open test1 for writing and ensure mtime increased from the previous value.
+    vfs.open("test1", "wt").close()
+    stat1_old = stat1
+    stat1 = vfs.stat("test1")
+    print(stat1_old[8] < stat1[8])
+
+    # Unmount.
+    vfs.umount()
+
+    # Check that remounting with mtime=False can read the timestamps.
+    print("mtime=False")
+    vfs = vfs_class(bdev, mtime=False)
+    print(vfs.stat("test1") == stat1)
+    print(vfs.stat("test2") == stat2)
+    f = vfs.open("test1", "wt")
+    f.close()
+    print(vfs.stat("test1") == stat1)
+    vfs.umount()
+
+    # Check that remounting with mtime=True still has the timestamps.
+    print("mtime=True")
+    vfs = vfs_class(bdev, mtime=True)
+    print(vfs.stat("test1") == stat1)
+    print(vfs.stat("test2") == stat2)
+    vfs.umount()
+
+
+bdev = RAMBlockDevice(30)
+test(bdev, uos.VfsLfs2)