Cache high-resolution mtimes for improved detection of modified files in v7
(and direct mode).
Including on Windows.
With back-compat support so old low-res mtimes won't break anything, and
so the new information also won't break old versions of git-annex.
I've seen intermittent failures of the test suite with v6 for a long time,
it seems to have possibly gotten worse with the changes around v7. Or just
being unlucky; all tests failed today.
Seen on amd64 and i386 builders, repeatedly but intermittently:
unused: FAIL (4.86s)
Test.hs:928:
git diff did not show changes to unlocked file
And I think other such failures, all involving v7/v6 mode tests.
I managed to reproduce the unused failure with --keep-failures,
and inside the repo, git diff was indeed not showing any changes for
the modified unlocked file.
The two stats will be the same other than mtime; the old and new files have
the same size and inode, since the test case writes to the file and then
overwrites it.
Indeed, notice the identical timestamps:
builder@orca:~/gitbuilder/build/.t/tmprepo335$ echo 1 > foo; stat foo; echo 2 > foo; stat foo
File: foo
Size: 2 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 3546179 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ builder) Gid: ( 1000/ builder)
Access: 2018-10-29 22:14:10.894942036 +0000
Modify: 2018-10-29 22:14:10.894942036 +0000
Change: 2018-10-29 22:14:10.894942036 +0000
Birth: -
File: foo
Size: 2 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 3546179 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 1000/ builder) Gid: ( 1000/ builder)
Access: 2018-10-29 22:14:10.894942036 +0000
Modify: 2018-10-29 22:14:10.898942036 +0000
Change: 2018-10-29 22:14:10.898942036 +0000
Birth: -
I'm seeing this in Linux VMs; it doesn't happen on my laptop. I've also
not experienced the intermittent test suite failures on my laptop.
So, I hope that this small delay will avoid the problem.
Update: I didn't, indeed I then reproduced the same failure on my
laptop, so it must be due to something else. But keeping this change anyway
since not needing to worry about lowish-resolution mtime in the test suite seems
worthwhile.
QuickCheck added an Arbitrary instance for CTime aka EpochTime. However,
while git-annex's instance disallowed times before the epoch, QuickCheck's
does not. So, rather than using its instance, convert from an Integer.
This commit was sponsored by Thomas Hochstein on Patreon.
Several tricky parts:
* When the conflict is just between the same key being locked and unlocked,
the unlocked version wins, and the file is not renamed in this case.
* Need to update associated file map when conflict resolution renames
an unlocked file.
* git merge runs the smudge filter on the conflicting file, and actually
overwrites the file with the same content it had before, and so
invalidates its inode cache. This makes it difficult to know when it's
safe to remove such files as conflict cruft, without going so far as to
compare their entire contents.
Dealt with this by preventing the smudge filter from populating the file
when a merge is run. However, that also prevents the smudge filter being
run for non-conflicting files, so eg moving a file won't put its new
content into place.
* Ideally, if a merge or a merge conflict resolution renames an unlocked
file, the file in the work tree can just be moved, rather than copying
the content to a new worktree file.
This is attempted to be done in merge conflict resolution, but
due to git merge's behavior of running smudge filters, what actually
seems to happen is the old worktree file with the content is deleted and
rewritten as a pointer file, so doesn't get reused.
So, this is probably not as efficient as it optimally could be.
If that becomes a problem, could look into running the merge in a separate
worktree and updating the real worktree more efficiently, similarly to the
direct mode merge. However, the direct mode merge had a lot of bugs, and
I'd rather not use that more error-prone method unless really needed.
The Keys database can hold multiple inode caches for a given key. One for
the annex object, and one for each pointer file, which may not be hard
linked to it.
Inode caches for a key are recorded when its content is added to the annex,
but only if it has known pointer files. This is to avoid the overhead of
maintaining the database when not needed.
When the smudge filter outputs a file's content, the inode cache is not
updated, because git's smudge interface doesn't let us write the file. So,
dropping will fall back to doing an expensive verification then. Ideally,
git's interface would be improved, and then the inode cache could be
updated then too.
This is necessary for interop between inode caches created on unix and
windows. Which is more important than supporting inodecaches for large keys
with the wrong size, which are broken anyway.
There should be no slowdown from this change, except on Windows.
Avoid using fileSize which maxes out at just 2 gb on Windows.
Instead, use hFileSize, which doesn't have a bounded size.
Fixes support for files > 2 gb on Windows.
Note that the InodeCache code only needs to compare a file size,
so it doesn't matter it the file size wraps. So it has been
left as-is. This was necessary both to avoid invalidating existing inode
caches, and because the code passed FileStatus around and would have become
more expensive if it called getFileSize.
This commit was sponsored by Christian Dietrich.
This fixes all instances of " \t" in the code base. Most common case
seems to be after a "where" line; probably vim copied the two space layout
of that line.
Done as a background task while listening to episode 2 of the Type Theory
podcast.
FileID type changed, needs Arbitrary instance.
On the plus side, getFileStatus on Windows now actually gets file id's,
not always 0, so direct mode is safer there now.
Rather than calculating the TSDelta once, and caching it, this now
reads the inode sential file's InodeCache file once, and then each time a
new InodeCache is generated, looks at the sentinal file to get the current
delta.
This way, if the time zone changes while git-annex is running, it will
adapt.
This adds some inneffiency, but only on Windows, and only 1 stat per new
file added. The worst innefficiency is that `git annex status` and
`git annex sync` will now (on Windows) stat the inode sentinal file once per
file in the repo.
It would be more efficient to use getCurrentTimeZone, rather than needing
to stat the sentinal file. This should be easy to do, once the time
package gets my bugfix patch.
This commit was sponsored by Jürgen Lüters.
On Windows, changing the time zone causes the apparent mtime of files to
change. This confuses git-annex, which natually thinks this means the files
have actually been modified (since THAT'S WHAT A MTIME IS FOR, BILL <sheesh>).
Work around this stupidity, by using the inode sentinal file to detect if
the timezone has changed, and calculate a TSDelta, which will be applied
when generating InodeCaches.
This should add no overhead at all on unix. Indeed, I sped up a few
things slightly in the refactoring.
Seems to basically work! But it has a big known problem:
If the timezone changes while the assistant (or a long-running command)
runs, it won't notice, since it only checks the inode cache once, and
so will use the old delta for all new inode caches it generates for new
files it's added. Which will result in them seeming changed the next time
it runs.
This commit was sponsored by Vincent Demeester.
Deal with FAT's low resolution timestamps, which in combination with
Linux's caching of higher res timestamps while a FAT is mounted, caused
direct mode repositories on FAT to seem to have modified files after they
were unmounted and remounted.
This commit was sponsored by Fabrice Rossi.
There are two types of equality here, and which one is right varies,
so this forces me to consider and choose between them.
Based on this, I learned that the commit in git anex sync was
always doing a strong comparison, even when in a repository where
the inodes had changed. Fixed that.
