view tests/test-origbackup-conflict.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

Set up repo

  $ cat << EOF >> $HGRCPATH
  > [ui]
  > origbackuppath=.hg/origbackups
  > [merge]
  > checkunknown=warn
  > EOF
  $ hg init repo
  $ cd repo
  $ echo base > base
  $ hg add base
  $ hg commit -m "base"

Make a dir named b that contains a file, and a file named d

  $ mkdir -p b
  $ echo c1 > b/c
  $ echo d1 > d
  $ hg add b/c d
  $ hg commit -m "c1"
  $ hg bookmark c1

Peform an update that causes b/c to be backed up

  $ hg up -q 0
  $ mkdir -p b
  $ echo c2 > b/c
  $ hg up --verbose c1
  resolving manifests
  b/c: replacing untracked file
  getting b/c
  creating directory: $TESTTMP/repo/.hg/origbackups/b
  getting d
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark c1)
  $ test -f .hg/origbackups/b/c

Make files named b and d

  $ hg up -q 0
  $ echo b1 > b
  $ echo d2 > d
  $ hg add b d
  $ hg commit -m b1
  created new head
  $ hg bookmark b1

Perform an update that causes b to be backed up - it should replace the backup b dir

  $ hg up -q 0
  $ echo b2 > b
  $ hg up --verbose b1
  resolving manifests
  b: replacing untracked file
  getting b
  removing conflicting directory: $TESTTMP/repo/.hg/origbackups/b
  getting d
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark b1)
  $ test -f .hg/origbackups/b

Perform an update the causes b/c to be backed up again - it should replace the backup b file

  $ hg up -q 0
  $ mkdir b
  $ echo c3 > b/c
  $ hg up --verbose c1
  resolving manifests
  b/c: replacing untracked file
  getting b/c
  creating directory: $TESTTMP/repo/.hg/origbackups/b
  removing conflicting file: $TESTTMP/repo/.hg/origbackups/b
  getting d
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark c1)
  $ test -d .hg/origbackups/b

Cause two symlinks to be backed up that points to a valid location from the backup dir

  $ hg up -q 0
  $ mkdir ../sym-link-target
#if symlink
  $ ln -s ../../../sym-link-target b
  $ ln -s ../../../sym-link-target d
#else
  $ touch b d
#endif
  $ hg up b1
  b: replacing untracked file
  d: replacing untracked file
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark b1)
#if symlink
  $ readlink.py .hg/origbackups/b
  .hg/origbackups/b -> ../../../sym-link-target
#endif

Perform an update that causes b/c and d to be backed up again - b/c should not go into the target dir

  $ hg up -q 0
  $ mkdir b
  $ echo c4 > b/c
  $ echo d3 > d
  $ hg up --verbose c1
  resolving manifests
  b/c: replacing untracked file
  d: replacing untracked file
  getting b/c
  creating directory: $TESTTMP/repo/.hg/origbackups/b
  removing conflicting file: $TESTTMP/repo/.hg/origbackups/b
  getting d
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark c1)
  $ cat .hg/origbackups/b/c
  c4
  $ cat .hg/origbackups/d
  d3
  $ ls ../sym-link-target

Incorrectly configure origbackuppath to be under a file

  $ echo data > .hg/badorigbackups
  $ hg up -q 0
  $ mkdir b
  $ echo c5 > b/c
  $ hg up --verbose c1 --config ui.origbackuppath=.hg/badorigbackups
  resolving manifests
  b/c: replacing untracked file
  getting b/c
  creating directory: $TESTTMP/repo/.hg/badorigbackups/b
  removing conflicting file: $TESTTMP/repo/.hg/badorigbackups
  getting d
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (activating bookmark c1)
  $ ls .hg/badorigbackups/b
  c