8 Commits

Author	SHA1	Message	Date
Christopher Haster	0ea2871e24	Fixed typo in scripts/readtree.py ... Not sure how this went unnoticed, I guess this is the first bug that needed in-depth inspection after the a last-minute argument cleanup in the debug scripts.	2020-11-22 15:05:22 -06:00
Christopher Haster	5137e4b0ba	Last minute tweaks to debug scripts ... - Standardized littlefs debug statements to use hex prefixes and brackets for printing pairs. - Removed the entry behavior for readtree and made -t the default. This is because 1. the CTZ skip-list parsing was broken, which is not surprising, and 2. the entry parsing was more complicated than useful. This functionality may be better implemented as a proper filesystem read script, complete with directory tree dumping. - Changed test.py's --gdb argument to take [init, main, assert], this matches the names of the stages in C's startup. - Added printing of tail to all mdir dumps in readtree/readmdir. - Added a print for if any mdirs are corrupted in readtree. - Added debug script side-effects to .gitignore.	2020-03-29 21:19:33 -05:00
Christopher Haster	a7dfae4526	Minor tweaks to debugging scripts, fixed explode_asserts.py off-by-1 ... - Changed readmdir.py to print the metadata pair and revision count, which is useful when debugging commit issues. - Added truncated data view to readtree.py by default. This does mean readtree.py must read all files on the filesystem to show the truncated data, hopefully this does not end up being a problem. - Made overall representation hopefully more readable, including moving superblock under the root dir, userattrs under files, fixing a gstate rendering issue. - Added rendering of soft-tails as dotted-arrows, hopefully this isn't too noisy. - Fixed explode_asserts.py off-by-1 in #line mapping caused by a strip call in the assert generation eating newlines. The script matches line numbers between the original+modified files by emitting assert statements that use the same number of lines. An off-by-1 here causes the entire file to map lines incorrectly, which can be very annoying.	2020-02-22 23:50:03 -06:00
Christopher Haster	6a550844f4	Modified readmdir/readtree to make reading non-truncated data easier ... Added indention so there was a more clear separation between the tag description and tag data. Also took the best parts of readmdir.py and added it to readtree.py. Initially I was thinking it was best for these to have completely independent data representations, since you could always call readtree to get more info, but this becomes tedius when needed to look at low-level tag info across multiple directories on the filesystem.	2020-02-09 12:00:23 -06:00
Christopher Haster	517d3414c5	Fixed more bugs, mostly related to ENOSPC on different geometries ... Fixes: - Fixed reproducability issue when we can't read a directory revision - Fixed incorrect erase assumption if lfs_dir_fetch exceeds block size - Fixed cleanup issue caused by lfs_fs_relocate failing when trying to outline a file in lfs_file_sync - Fixed cleanup issue if we run out of space while extending a CTZ skip-list - Fixed missing half-orphans when allocating blocks during lfs_fs_deorphan Also: - Added cycle-detection to readtree.py - Allowed pseudo-C expressions in test conditions (and it's beautifully hacky, see line 187 of test.py) - Better handling of ctrl-C during test runs - Added build-only mode to test.py - Limited stdout of test failures to 5 lines unless in verbose mode Explanation of fixes below 1. Fixed reproducability issue when we can't read a directory revision An interesting subtlety of the block-device layer is that the block-device is allowed to return LFS_ERR_CORRUPT on reads to untouched blocks. This can easily happen if a user is using ECC or some sort of CMAC on their blocks. Normally we never run into this, except for the optimization around directory revisions where we use uninitialized data to start our revision count. We correctly handle this case by ignoring whats on disk if the read fails, but end up using unitialized RAM instead. This is not an issue for normal use, though it can lead to a small information leak. However it creates a big problem for reproducability, which is very helpful for debugging. I ended up running into a case where the RAM values for the revision count was different, causing two identical runs to wear-level at different times, leading to one version running out of space before a bug occured because it expanded the superblock early. 2. Fixed incorrect erase assumption if lfs_dir_fetch exceeds block size This could be caused if the previous tag was a valid commit and we lost power causing a partially written tag as the start of a new commit. Fortunately we already have a separate condition for exceeding the block size, so we can force that case to always treat the mdir as unerased. 3. Fixed cleanup issue caused by lfs_fs_relocate failing when trying to outline a file in lfs_file_sync Most operations involving metadata-pairs treat the mdir struct as entirely temporary and throw it out if any error occurs. Except for lfs_file_sync since the mdir is also a part of the file struct. This is relevant because of a cleanup issue in lfs_dir_compact that usually doesn't have side-effects. The issue is that lfs_fs_relocate can fail. It needs to allocate new blocks to relocate to, and as the disk reaches its end of life, it can fail with ENOSPC quite often. If lfs_fs_relocate fails, the containing lfs_dir_compact would return immediately without restoring the previous state of the mdir. If a new commit comes in on the same mdir, the old state left there could corrupt the filesystem. It's interesting to note this is forced to happen in lfs_file_sync, since it always tries to outline the file if it gets ENOSPC (ENOSPC can mean both no blocks to allocate and that the mdir is full). I'm not actually sure this bit of code is necessary anymore, we may be able to remove it. 4. Fixed cleanup issue if we run out of space while extending a CTZ skip-list The actually CTZ skip-list logic itself hasn't been touched in more than a year at this point, so I was surprised to find a bug here. But it turns out the CTZ skip-list could be put in an invalid state if we run out of space while trying to extend the skip-list. This only becomes a problem if we keep the file open, clean up some space elsewhere, and then continue to write to the open file without modifying it. Fortunately an easy fix. 5. Fixed missing half-orphans when allocating blocks during lfs_fs_deorphan This was a really interesting bug. Normally, we don't have to worry about allocations, since we force consistency before we are allowed to allocate blocks. But what about the deorphan operation itself? Don't we need to allocate blocks if we relocate while deorphaning? It turns out the deorphan operation can lead to allocating blocks while there's still orphans and half-orphans on the threaded linked-list. Orphans aren't an issue, but half-orphans may contain references to blocks in the outdated half, which doesn't get scanned during the normal allocation pass. Fortunately we already fetch directory entries to check CTZ lists, so we can also check half-orphans here. However this causes lfs_fs_traverse to duplicate all metadata-pairs, not sure what to do about this yet.	2020-02-09 11:54:22 -06:00
Christopher Haster	a5d614fbfb	Added tests for power-cycled-relocations and fixed the bugs that fell out ... The power-cycled-relocation test with random renames has been the most aggressive test applied to littlefs so far, with: - Random nested directory creation - Random nested directory removal - Random nested directory renames (this could make the threaded linked-list very interesting) - Relocating blocks every write (maximum wear-leveling) - Incrementally cycling power every write Also added a couple other tests to test_orphans and test_relocations. The good news is the added testing worked well, it found quite a number of complex and subtle bugs that have been difficult to find. 1. It's actually possible for our parent to be relocated and go out of sync in lfs_mkdir. This can happen if our predecessor's predecessor is our parent as we are threading ourselves into the filesystem's threaded list. (note this doesn't happen if our predecessor _is_ our parent, as we then update our parent in a single commit). This is annoying because it only happens if our parent is a long (>1 pair) directory, otherwise we wouldn't need to catch relocations. Fortunately we can reuse the internal open file/dir linked-list to catch relocations easily, as long as we're careful to unhook our parent whenever lfs_mkdir returns. 2. Even more surprising, it's possible for the child in lfs_remove to be relocated while we delete the entry from our parent. This can happen if we are our own parent's predecessor, since we need to be updated then if our parent relocates. Fortunately we can also hook into the open linked-list here. Note this same issue was present in lfs_rename. Fortunately, this means now all fetched dirs are hooked into the open linked-list if they are needed across a commit. This means we shouldn't need assumptions about tree movement for correctness. 3. lfs_rename("deja/vu", "deja/vu") with the same source and destination was broken and tried to delete the entry twice. 4. Managing gstate deltas when we lose power during relocations was broken. And unfortunately complicated. The issue happens when we lose power during a relocation while removing a directory. When we remove a directory, we need to move the contents of its gstate delta to another directory or we'll corrupt littlefs gstate. (gstate is an xor of all deltas on the filesystem). We used to just xor the gstate into our parent's gstate, however this isn't correct. The gstate isn't built out of the directory tree, but rather out of the threaded linked-list (which exists to make collecting this gstate efficient). Because we have to remove our dir in two operations, there's a point were both the updated parent and child can exist in threaded linked-list and duplicate the child's gstate delta. .--------. ->| parent |-. | gstate | | .-| a |-' | '--------' | X <- child is orphaned | .--------. '>| child |-> | gstate | | a | '--------' What we need to do is save our child's gstate and only give it to our predecessor, since this finalizes the removal of the child. However we still need to make valid updates to the gstate to mark that we've created an orphan when we start removing the child. This led to a small rework of how the gstate is handled. Now we have a separation of the gpending state that should be written out ASAP and the gdelta state that is collected from orphans awaiting deletion. 5. lfs_deorphan wasn't actually able to handle deorphaning/desyncing more than one orphan after a power-cycle. Having more than one orphan is very rare, but of course very possible. Fortunately this was just a mistake with using a break the in the deorphan, perhaps left from v1 where multiple orphans weren't possible? Note that we use a continue to force a refetch of the orphaned block. This is needed in the case of a half-orphan, since the fetched half-orphan may have an outdated tail pointer.	2020-01-26 23:45:54 -06:00
Christopher Haster	f4b6a6b328	Fixed issues with neighbor updates during moves ... The root of the problem was some assumptions about what tags could be sent to lfs_dir_commit. - The first assumption is that there could be only one splice (create/delete) tag at a time, which is trivially broken by the core commit in lfs_rename. - The second assumption is that there is at most one create and one delete in a single commit. This is less obvious but turns out to not be true in the case that we rename a file such that it overwrites another file in the same directory (1 delete for source file, 1 delete for destination). - The third assumption was that there was an ordering to the delete/creates passed to lfs_dir_commit. It may be possible to force all deletes to follow creates by rearranging the tags in lfs_rename, but this risks overflowing tag ids. The way the lfs_dir_commit first collected the "deletetag" and "createtag" broke all three of these assumptions. And because we lose the ordering information we can no longer apply the directory changes to open files correctly. The file ids may be shifted in a way that doesn't reflect the actual operations on disk. These problems were made worst by lfs_dir_commit cleaning up moves implicitly, which also creates deletes implicitly. While cleaning up moves in lfs_dir_commit may save some code size, it makes the commit logic much more difficult to implement correctly. This bug turned into pulling out a dead tree stump, roots and all. I ended up reworking how lfs_dir_commit updates open files so that it has less assumptions, now it just traverses the commit tags multiple times in order to update file ids after a successful commit in the correct order. This also got rid of the dir copy by carefully updating split dirs after all files have an up-to-date copy of the original dir. I also just removed the implicit move cleanup. It turns out the only commits that can occur before we have cleaned up the move is in lfs_fs_relocate, so it was simple enough to explicitly handle this case when we update our parent and pred during a relocate. Cases where we may need to fix moves: - In lfs_rename when we move a file/dir - In lfs_demove if we lose power - In lfs_fs_relocate if we have to relocate our parent and we find it had a pending move (or else the move will be outdated) - In lfs_fs_relocate if we have to relocate our predecessor and we find it had a pending move (or else the move will be outdated) Note the two cases in lfs_fs_relocate may be recursive. But lfs_fs_relocate can only trigger other lfs_fs_relocates so it's not possible for pending moves to spill out into other filesystem commits And of couse, I added several tests to cover these situations. Hopefully the rename-with-open-files logic should be fairly locked down now. found with initial fix by eastmoutain	2020-01-20 19:27:27 -06:00
Christopher Haster	9453ebd15d	Added/improved disk-reading debug scripts ... Also fixed a bug in dir splitting when there's a large number of open files, which was the main reason I was trying to make it easier to debug disk images. One part of the recent test changes was to move away from the file-per-block emubd and instead simulate storage with a single contiguous file. The file-per-block format was marginally useful at the beginning, but as the remaining bugs get more subtle, it becomes more useful to inspect littlefs through scripts that make the underlying metadata more human-readable. The key benefit of switching to a contiguous file is these same scripts can be reused for real disk images and can even read through /dev/sdb or similar. - ./scripts/readblock.py disk block_size block off data 00000000: 71 01 00 00 f0 0f ff f7 6c 69 74 74 6c 65 66 73 q.......littlefs 00000010: 2f e0 00 10 00 00 02 00 00 02 00 00 00 04 00 00 /............... 00000020: ff 00 00 00 ff ff ff 7f fe 03 00 00 20 00 04 19 ............... 00000030: 61 00 00 0c 00 62 20 30 0c 09 a0 01 00 00 64 00 a....b 0......d. ... readblock.py prints a hex dump of a given block on disk. It's basically just "dd if=disk bs=block_size count=1 skip=block | xxd -g1 -" but with less typing. - ./scripts/readmdir.py disk block_size block1 block2 off tag type id len data (truncated) 0000003b: 0020000a dir 0 10 63 6f 6c 64 63 6f 66 66 coldcoff 00000049: 20000008 dirstruct 0 8 02 02 00 00 03 02 00 00 ........ 00000008: 00200409 dir 1 9 68 6f 74 63 6f 66 66 65 hotcoffe 00000015: 20000408 dirstruct 1 8 fe 01 00 00 ff 01 00 00 ........ readmdir.py prints info about the tags in a metadata pair on disk. It can print the currently active tags as well as the raw log of the metadata pair. - ./scripts/readtree.py disk block_size superblock "littlefs" version v2.0 block_size 512 block_count 1024 name_max 255 file_max 2147483647 attr_max 1022 gstate 0x000000000000000000000000 dir "/" mdir {0x0, 0x1} rev 3 v id 0 superblock "littlefs" inline size 24 mdir {0x77, 0x78} rev 1 id 0 dir "coffee" dir {0x1fc, 0x1fd} dir "/coffee" mdir {0x1fd, 0x1fc} rev 2 id 0 dir "coldcoffee" dir {0x202, 0x203} id 1 dir "hotcoffee" dir {0x1fe, 0x1ff} dir "/coffee/coldcoffee" mdir {0x202, 0x203} rev 1 dir "/coffee/warmcoffee" mdir {0x200, 0x201} rev 1 readtree.py parses the littlefs tree and prints info about the semantics of what's on disk. This includes the superblock, global-state, and directories/metadata-pairs. It doesn't print the filesystem tree though, that could be a different tool.	2020-01-20 19:27:27 -06:00