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.
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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.
The code-cost wasn't that bad: 16556 B -> 16754 B (+1.2%)
But moving write support of older versions behind a compile-time flag
allows us to be a bit more liberal with what gets added to support older
versions, since the cost won't hit most users.
The intention is to help interop with older minor versions of littlefs.
Unfortunately, since lfs2.0 drivers cannot mount lfs2.1 images, there are
situations where it would be useful to write to write strictly lfs2.0
compatible images. The solution here adds a "disk_version" configuration
option which determines the behavior of lfs2.1 dependent features.
Normally you would expect this to only change write behavior. But since the
main change in lfs2.1 increased validation of erased data, we also need to
skip this extra validation (fcrc) or see terrible slowdowns when writing.
In terms of ease-of-use, a user familiar with other filesystems expects
block_usage in fsinfo. But in terms of practicality, block_usage can be
expensive to find in littlefs, so if it's not needed in the resulting
fsinfo, that operation is wasteful.
It's not clear to me what the best course of action is, but since
block_usage can always be added to fsinfo later, but not removed without
breaking backwards compatibility, I'm leaving this out for now.
Block usage can still be found by explicitly calling lfs_fs_size.
ChaN's FAT implementation definitely deserves a mention here, since it
was one of the first open-source microcontroller-oriented filesystem
implementations that I'm aware of, and has a lot of good ideas at the
implementation level.
Honestly I didn't realize this wasn't already linked to from here. If
you're using FAT on a microcontroller, it's most likely this library.
Version are now returned with major/minor packed into 32-bits,
so 0x00020001 is the current disk version, for example.
1. This needed to change to use a disk_* prefix for consistency with the
defines that already exist for LFS_VERSION/LFS_DISK_VERSION.
2. Encoding the version this way has the nice side effect of making 0 an
invalid value. This is useful for adding a similar config option
that needs to have reasonable default behavior for backwards
compatibility.
In theory this uses more space, but in practice most other config/status
is 32-bits in littlefs. We would be wasting this space for alignment
anyways.
This function naturally doesn't exist in the previous version. We should
eventually add these calls when we can expect the previous version to
support this function, though it's a bit unclear when that should happen.
Or maybe not! Maybe this is testing more of the previous version than we
really care about.
LFS_VERSION -> LFS_DISK_VERSION
These tests shouldn't depend on LFS_VERSION. It's a bit subtle, but
LFS_VERSION versions the API, and LFS_DISK_VERSION versions the
on-disk format, which is what test_compat should be testing.
Currently this includes:
- minor_version - on-disk minor version
- block_usage - estimated number of in-use blocks
- name_max - configurable name limit
- file_max - configurable file limit
- attr_max - configurable attr limit
These are currently the only configuration operations that need to be
written to disk. Other configuration is either needed to mount, such as
block_size, or does not change the on-disk representation, such as
read/prog_size.
This also includes the current block usage, which is common in other
filesystems, though a more expensive to find in littlefs. I figure it's
not unreasonable to make lfs_fs_stat no worse than block allocation,
hopefully this isn't a mistake. It may be worth caching the current
usage after the most recent lookahead scan.
More configuration may be added to this struct in the future.
Likely included at some point for ssize_t, this is no longer needed and
causes some problems for embedded compilers.
Currently littlefs doesn't even use size_t/ssize_t in its definition of
lfs_size_t/lfs_ssize_t, so I don't think this will ever be required.
Found by LDong-Arm, vvn-git
This fixes the overflowing left shift on 8 bit platforms.
littlefs2/lfs.c: In function ‘lfs_dir_commitcrc’:
littlefs2/lfs.c:1654:51: error: left shift count >= width of type [-Werror=shift-count-overflow]
commit->ptag = ntag ^ ((0x80 & ~eperturb) << 24);
With the new test framework, GitHub really wants to mark littlefs as a
python project. telling it to reclassify our test .toml files as C code
(which they are 95% of anyways) remedies this.
An alternative would be to add syntax=c vim modelines to the test/bench
files, which would also render them with C syntax highlighting on
GitHub. Unfortunately the interspersed toml metadata mucks this up,
making the result not very useful.
Christopher Haster