Fix metadata_max==prog_size commit->end calculation #1031
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- Added METADATA_MAX to test_runner. - Added METADATA_MAX to bench_runner. - Added a simple metadata_max test to test_superblocks, for lack of better location. There have been several issues floating around related to metadata_max and LFS_ERR_NOSPC which makes me think there's a bug in our metadata_max logic. metadata_max was a quick patch and is relatively untested, so an undetected bug isn't too surprising. This commit adds at least some testing over metadata_max. Sure enough, the new test_superblocks_metadata_max test reveals a curious LFS_ERR_NAMETOOLONG error that shouldn't be there. More investigation needed.
The inconsistency here between the use of block_size vs metadata_max was suspicious. Turns out there's a bug when metadata_max == prog_size. We correctly use metadata_max for the block_size/2 check, but we weren't using it for the block_size-40 check. The second check seems unnecessary after the first, but it protects against running out of space in a commit for commit-related metadata (checksums, tail pointers, etc) when we can't program half-blocks. Turns out this is also needed when limiting metadata_max to a single prog, otherwise we risk erroring with LFS_ERR_NOSPC early. Found by ajheck, dpkristensen, NLLK, and likely others.
Like the read/prog/block_size checks, these are just asserts. If these invariants are broken the filesystem will break in surprising ways.
This was referenced Oct 4, 2024
Tests passed ✓, Code: 17068 B, Stack: 1440 B, Structs: 812 B
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I've been trying to dig into some of the early LFS_ERR_NOSPC errors users have been seeing. Some of the problem is that littlefs returns LFS_ERR_NOSPC for both "no space" errors, and internally whenever metadata can't fit in a block/mdir. This has made tracking down the actual root cause a bit tricky.
I did at least find one bug: In mdir compaction we weren't correctly adjusting
commit->endto reserve space for commit-related metadata (checksums, tail pointers, etc) whenmetadata_max==prog_size.This went unnoticed due to a lack of testing and requiring
metadata_max==prog_size.Added a quick test to prevent regression, and also added a few more asserts to
lfs_initrelated to possiblemetadata_maxconfiguration mistakes.Found by @ajheck, @dpkristensen, @NLLK, and likely others.
Related #755, #896