This drops the lookahead buffer from operating on 32-bit words to
operating on 8-bit bytes, and removes any alignment requirement. This
may have some minor performance impact, but it is unlikely to be
significant when you consider IO overhead.
The original motivation for 32-bit alignment was an attempt at
future-proofing in case we wanted some more complex on-disk data
structure. This never happened, and even if it did, it could have been
added via additional config options.
This has been a significant pain point for users, since providing
word-aligned byte-sized buffers in C can be a bit annoying.
- Renamed lfs.free -> lfs.lookahead
- Renamed lfs.free.off -> lfs.lookahead.start
- Renamed lfs.free.i -> lfs.lookahead.next
- Renamed lfs.free.ack -> lfs.lookahead.ckpoint
- Renamed lfs_alloc_ack -> lfs_alloc_ckpoint
These have been named a bit confusingly, and I think the new names make
their relevant purposes a bit clearer.
At the very it's clear lfs.lookahead is related to the lookahead buffer.
(and doesn't imply a closed free-bitmap).
Superblock expansion is an irreversible operation. In an effort to
prevent superblock expansion from claiming valuable scratch space
(important for small, <~8 block filesystems), littlefs prevents
superblock expansion when the disk is "mostly full".
In true computer-scientist fashion, this "mostly full" threshold was
set to ~50%.
As pointed out by gbolgradov and rojer, >~50% utilization is not
uncommon, and it can lead to a situation where superblock expansion does
not occur in a relatively healthy filesystem, causing focused wear at
the root.
To remedy this, the threshold is now increased to ~88% (7/8) full.
This may change in the future and should probably be eventually user
configurable.
Found by gbolgradov and rojer
Now you can override littlefs's CRC implementation with some simple
defines:
-DLFS_CRC=lfs_crc
The motivation for this is the same for LFS_MALLOC/LFS_FREE. I think
these are the main "system-level" utils that users want to override.
Don't override with this something that's not CRC32! Your filesystem
will no longer be compatible with other tools! This is only intended for
provided hardware acceleration!
Now you can override littlefs's malloc with some simple defines:
-DLFS_MALLOC=my_malloc
-DLFS_FREE=my_free
This is probably what most users expected when wanting to override
malloc/free in littlefs, but it hasn't been available, since instead
littlefs provides a file-level override of builtin utils.
The thinking was that there's just too many builtins that could be
overriden, lfs_max/min/alignup/npw2/etc/etc/etc, so allowing users to
just override the util file provides the best flexibility without a ton
of ifdefs.
But it's become clear this is awkward for users that just want to
replace malloc.
Maybe the original goal was too optimistic, maybe there's a better way
to structure this file, or maybe the best API is just a bunch of ifdefs,
I have no idea! This will hopefully continue to evolve.
This warning is useful for catching the easy mistake of missing the
keyword static on functions intended to be internal-only.
Missing the static keyword risks symbol polution and misses potential
compiler optimizations.
This is an interesting warning, while useful for libraries such as
littlefs, it's perfectly valid C to not predeclare all functions, and
common in final application binaries.
Relatedly, this warning is re-disabled for the test/bench runner. There
may be a better way to organize the CFLAGS, maybe into separate
LIB/RUNNER CFLAGS, but I'll leave this to future work if our CFLAGS grow
more complicated.
This was motivated by non-static internal-only functions leaking into a
release. Found and fixed by DvdGiessen.
The idea is in the future this function may be extended to support other
block janitorial work. In such a case calling this lfs_fs_gc provides a
more general name that can include other operations.
This is currently just wishful thinking, however.
- Test that the code actually runs.
- Test that lfs_fs_findfreeblocks does not break block allocations.
- Test that lfs_fs_findfreeblocks does not error when no space is
available, it should only errors when the block is actually needed.
The initial implementation for this was provided by kaetemi, originally
as a mount flag. However, it has been modified here to be self-contained
in an explicit runtime function that can be called after mount.
The reasons for an explicit function:
1. lfs_mount stays a strictly readonly operation, and avoids pulling in
all of the write machinery.
2. filesystem-wide operations such as lfs_fs_grow can be a bit risky,
and irreversable. The action of growing the filesystem should be very
intentional.
---
One concern with this change is that this will be the first function
that changes metadata in the superblock. This might break tools that
expect the first valid superblock entry to contain the most recent
metadata, since only the last superblock in the superblock chain will
contain the updated metadata.
In separating the configuration of littlefs from the physical geometry
of the underlying device, we can no longer rely solely on lfs_config to
contain all of the information necessary for the simulated block devices
we use for testing.
This adds a new lfs_*bd_config struct for each of the block devices, and
new erase_size/erase_count fields. The erase_* name was chosen since
these reflect the (simulated) physical erase size and count of
erase-sized blocks, unlike the block_* variants which represent logical
block sizes used for littlefs's bookkeeping.
It may be worth adopting erase_size/erase_count in littlefs's config at
some point in the future, but at the moment doesn't seem necessary.
Changing the lfs_bd_config structs to be required is probably a good
idea anyways, as it moves us more towards separating the bds from
littlefs. Though we can't quite get rid of the lfs_config parameter
because of the block-device API in lfs_config. Eventually it would be
nice to get rid of it, but that would require API breakage.
This can't actually happen in the current state of the littlefs GitHub
repo, but could in theory cause problems if CI is enabled on a fork.
Found while enabling GitHub Actions on littlefs-fuse.
