Like most of the lfs_dir_t functions, lfs_dir_append is responsible for
updating the lfs_dir_t struct if the underlying directory block is
moved. This property makes handling worn out blocks much easier by
removing the amount of state that needs to be considered during a
directory update.
However, extending the dir chain is a bit of a corner case. It's not
changing the old block, but callers of lfs_dir_append do assume the
"entry" will reside in "dir" after lfs_dir_append completes.
This issue only occurs when creating files, since mkdir does not use
the entry after lfs_dir_append. Unfortunately, the tests against
extending the directory chain were all made using mkdir.
Found by schouleu
Before this patch, when calling lfs_mkdir or lfs_file_open with root
as the target, littlefs wouldn't find the path properly and happily
run into undefined behaviour.
The fix is to populate a directory entry for root in the lfs_dir_find
function. As an added plus, this allowed several special cases around
root to be completely dropped.
Note: It's still expected to modify lfs_utils.h when porting littlefs
to a new target/system. There's just too much room for system-specific
improvements, such as taking advantage of CRC hardware.
Rather, encouraging modification of lfs_util.h and making it easy to
modify and debug should result in better integration with the consuming
systems.
This just adds a bunch of quality-of-life improvements that should help
development and integration in littlefs.
- Macros that require no side-effects are all-caps
- System includes are only brought in when needed
- Malloc/free wrappers
- LFS_NO_* checks for quickly disabling things at the command line
- At least a little-bit more docs
Required to support big-endian processors, with the most notable being
the PowerPC architecture.
On little-endian architectures, these conversions can be optimized out
and have no code impact.
Initial patch provided by gmouchard
Rather than tracking all in-flight blocks blocks during a lookahead,
littlefs uses an ack scheme to mark the first allocated block that
hasn't reached the disk yet. littlefs assumes all blocks since the
last ack are bad or in-flight, and uses this to know when it's out
of storage.
However, these unacked allocations were still being populated in the
lookahead buffer. If the whole block device fits in the lookahead
buffer, _and_ littlefs managed to scan around the whole storage while
an unacked block was still in-flight, it would assume the block was
free and misallocate it.
The fix is to only fill the lookahead buffer up to the last ack.
The internal free structure was restructured to simplify the runtime
calculation of lookahead size.
- Write on read-only file to return LFS_ERR_BADF
- Renaming directory onto file to return LFS_ERR_NOTEMPTY
- Changed LFS_ERR_INVAL in lfs_file_seek to assert
An annoying part of filesystems is that the software library can change
independently of the on-disk structures. For this reason versioning is
very important, and must be handled separately for the software and
on-disk parts.
In this patch, littlefs provides two version numbers at compile time,
with major and minor parts, in the form of 6 macros.
LFS_VERSION // Library version, uint32_t encoded
LFS_VERSION_MAJOR // Major - Backwards incompatible changes
LFS_VERSION_MINOR // Minor - Feature additions
LFS_DISK_VERSION // On-disk version, uint32_t encoded
LFS_DISK_VERSION_MAJOR // Major - Backwards incompatible changes
LFS_DISK_VERSION_MINOR // Minor - Feature additions
Note that littlefs will error if it finds a major version number that
is different, or a minor version number that has regressed.
As a copy-on-write filesystem, the truncate function is a very nice
function to have, as it can take advantage of reusing the data already
written out to disk.
Unfortunately for us, the ctz skip-list does not offer very much benefit
for full traversals. Since the information about which blocks are in
use are spread throughout the file, we can't use the fast-lanes
embedded in the skip-list without missing blocks.
However, it turns out we can at least use the 2nd level of the skip-list
without missing any blocks. From an asymptotic analysis, a constant speed
up isn't interesting, but from a pragmatic perspective, a 2x speedup is
not bad.
littlefs had an unwritten assumption that the block device's program
size would be a multiple of the read size, and the block size would
be a multiple of the program size. This has already caused confusion
for users. Added a note and assert to catch unexpected geometries
early.
Also found that the prog/erase functions indicated they must return
LFS_ERR_CORRUPT to catch bad blocks. This is no longer true as errors
are found by CRC.
In the open call, the LFS_O_TRUNC flag was correctly zeroing the file, but
it wasn't actually writing the change out to disk. This went unnoticed because
in the cases where the truncate was followed by a file write, the
updated contents would be written out correctly.
Marking the file as dirty if the file isn't already truncated fixes the
problem with the least impact. Also added better test cases around
truncating files.
This bug was a result of an annoying corner case around intermingling
signed and unsigned offsets. The boundary check that prevents seeking
a file to a position before the file was preventing valid seeks with
positive offsets.
This corner case is a bit more complicated than it looks because the
offset is signed, while the size of the file is unsigned. Simply
casting both to signed or unsigned offsets won't handle large files.
This was a small hole in the logic that handles initializing the
lookahead buffer. To imitate exhaustion (so the block allocator
will trigger a scan), the lookahead buffer is rewound a full
lookahead and set up to look like it is exhausted. However,
unlike normal allocation, this rewind was not kept aligned to
a multiple of the scan size, which is limited by both the
lookahead buffer and the total storage size.
This bug went unnoticed for so long because it only causes
problems when the block device is both:
1. Not aligned to the lookahead buffer (not a power of 2)
2. Smaller than the lookahead buffer
While this seems like a strange corner case for a block device,
this turned out to be very common for internal flash, especially
when a handleful of blocks are reserved for code.
As it was, if a user operated on a directory while at the same
time iterating over the directory, the directory objects could
fall out of sync. In the best case, files may be skipped while
removing everything in a file, in the worst case, a very poorly
timed directory relocate could be missed.
Simple fix is to add the same directory tracking that is currently
in use for files, at a small code+complexity cost.
Short story, files are no longer committed to directories during
file sync/close if the last write did not complete successfully.
This avoids a set of interesting user-experience issues related
to the end-of-life behaviour of the filesystem.
As a filesystem approaches end-of-life, the chances of running into
LFS_ERR_NOSPC grows rather quickly. Since this condition occurs after
at the end of a devices life, it's likely that operating in these
conditions hasn't been tested thoroughly.
In the specific case of file-writes, you can hit an LFS_ERR_NOSPC after
parts of the file have been written out. If the program simply continues
and closes the file, the file is written out half completed. Since
littlefs has a strong garuntee the prevents half-writes, it's unlikely
this state of the file would be expected.
To make things worse, since close is also responsible for memory
cleanup, it's actually _impossible_ to continue working as it was
without leaking memory.
By prevent the file commits, end-of-life behaviour should at least retain
a previous copy of the filesystem without any surprises.
Specifically around error handling. As is, incorrectly handled
errors could cause higher code to get uninitialized blocks,
potentially leading to writes to arbitray blocks on storage.
This is only an issue in the weird case that are worn down block is
left in the odd state of not being able to change the data that resides
on the block. That being said, this does pop up often when simulating
wear on block devices.
Currently, directory commits checked if the write succeeded by crcing the
block to avoid the additional RAM cost for another buffer. However,
before this commit, directory commits just checked if the block crc was
valid, rather than comparing to the expected crc. This would usually
work, unless the block was stuck in a state with valid crc.
The fix is to simply compare with the expected crc to find errors.
The previous math for determining if we scanned all of disk wasn't set
up correctly in the lfs_mount function. If lookahead == block_count
the lfs_alloc function would think we had already searched the entire
disk.
This is only an issue if we manage to exhaust a block on the first
pass after mount, since lfs_alloc_ack resets the lookahead region
into a valid state after a succesful block allocation.
The littlefs allows buffers to be passed statically in the case
that a system does not have a heap. Unfortunately, this means we
can't round up in the case of an unaligned lookahead buffer.
Double unfortunately, rounding down after clamping to the block device
size could result in a lookahead of zero for block devices < 32 blocks
large.
The assert in littlefs does catch this case, but rounding down prevents
support for < 32 block devices.
The solution is to simply require a 32-bit aligned buffer with an
assert. This avoids runtime problems while allowing a user to pass
in the correct buffer for < 32 block devices. Rounding up can be
handled at higher API levels.
