Mercurial > hg
view tests/test-issue672.t @ 46607:e9901d01d135
revlog: add a mechanism to verify expected file position before appending
If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.
The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)
When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.
For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.
This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.
Differential Revision: https://phab.mercurial-scm.org/D9952
author | Kyle Lippincott <spectral@google.com> |
---|---|
date | Wed, 03 Feb 2021 16:33:10 -0800 |
parents | 69429972ff1f |
children | 38941a28406a |
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https://bz.mercurial-scm.org/672 # 0-2-4 # \ \ \ # 1-3-5 # # rename in #1, content change in #4. $ hg init $ touch 1 $ touch 2 $ hg commit -Am init # 0 adding 1 adding 2 $ hg rename 1 1a $ hg commit -m rename # 1 $ hg co -C 0 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ echo unrelated >> 2 $ hg ci -m unrelated1 # 2 created new head $ hg merge --debug 1 unmatched files in other: 1a all copies found (* = to merge, ! = divergent, % = renamed and deleted): on remote side: src: '1' -> dst: '1a' checking for directory renames resolving manifests branchmerge: True, force: False, partial: False ancestor: 81f4b099af3d, local: c64f439569a9+, remote: c12dcd37c90a 1: other deleted -> r removing 1 1a: remote created -> g getting 1a 1 files updated, 0 files merged, 1 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg ci -m merge1 # 3 $ hg co -C 2 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ echo hello >> 1 $ hg ci -m unrelated2 # 4 created new head $ hg co -C 3 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg merge -y --debug 4 unmatched files in local: 1a all copies found (* = to merge, ! = divergent, % = renamed and deleted): on local side: src: '1' -> dst: '1a' * checking for directory renames resolving manifests branchmerge: True, force: False, partial: False ancestor: c64f439569a9, local: f4a9cff3cd0b+, remote: 746e9549ea96 starting 4 threads for background file closing (?) preserving 1a for resolve of 1a 1a: local copied/moved from 1 -> m (premerge) picked tool ':merge' for 1a (binary False symlink False changedelete False) merging 1a and 1 to 1a my 1a@f4a9cff3cd0b+ other 1@746e9549ea96 ancestor 1@c64f439569a9 premerge successful 0 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit) $ hg co -C 4 1 files updated, 0 files merged, 1 files removed, 0 files unresolved $ hg merge -y --debug 3 unmatched files in other: 1a all copies found (* = to merge, ! = divergent, % = renamed and deleted): on remote side: src: '1' -> dst: '1a' * checking for directory renames resolving manifests branchmerge: True, force: False, partial: False ancestor: c64f439569a9, local: 746e9549ea96+, remote: f4a9cff3cd0b starting 4 threads for background file closing (?) preserving 1 for resolve of 1a removing 1 1a: remote moved from 1 -> m (premerge) picked tool ':merge' for 1a (binary False symlink False changedelete False) merging 1 and 1a to 1a my 1a@746e9549ea96+ other 1a@f4a9cff3cd0b ancestor 1@c64f439569a9 premerge successful 0 files updated, 1 files merged, 0 files removed, 0 files unresolved (branch merge, don't forget to commit)