49 lines
2.4 KiB
Markdown
49 lines
2.4 KiB
Markdown
Started the day by getting the builds updated for yesterday's release. This
|
|
included making it possible to build git-annex with Debian stable's version
|
|
of cryptohash. Also updated the Debian stable backport to the previous
|
|
release.
|
|
|
|
----
|
|
|
|
The [[design/roadmap]] has this month devoted to improving git-annex's
|
|
support for recovering from disasters, broken repos, and so on. Today I've
|
|
been working on the first thing on [[the_list|design/assistant/disaster_recovery]],
|
|
stale git index lock files.
|
|
|
|
It's unfortunate that git uses simple files for locking, and does not use
|
|
fcntl or flock to prevent the stale lock file problem. Perhaps they want
|
|
it to work on broken NFS systems? The problem with that line of thinking is
|
|
is means all non-broken systems end up broken by stale lock files. Not a
|
|
good tradeoff IMHO.
|
|
|
|
There are actually two lock files that can end up stale when using
|
|
git-annex; both `.git/index.lock` and `.git/annex/index.lock`. Today I
|
|
concentrated on the latter, because I saw a way to prevent it from ever
|
|
being a problem. All updates to that index file are done by git-annex when
|
|
committing to the git-annex branch. git-annex already uses fcntl locking
|
|
when manipulating its journal. So, that can be extended to also cover
|
|
committing to the git-annex branch, and then the git `index.lock` file
|
|
is irrelevant, and can just be removed if it exists when a commit is
|
|
started.
|
|
|
|
To ensure this makes sense, I used the type system to prove that the journal
|
|
locking was in effect everywhere I need it to be. Very happy I was able to
|
|
do that, although I am very much a novice at using the type system for
|
|
interesting proofs. But doing so made it very easily to build up to a point
|
|
where I could unlink the `.git/annex/index.lock` and be sure it was safe to do
|
|
that.
|
|
|
|
----
|
|
|
|
What about stale `.git/index.lock` files? I don't think it's appropriate
|
|
for git-annex to generally recover from those, because it would change
|
|
regular git command line behavior, and risks breaking something. However, I
|
|
do want the assistant to be able to recover if such a file exists when it
|
|
is starting up, since that would prevent it from running. Implemented that
|
|
also today, although I am less happy with the way the assistant detects
|
|
when this lock file is stale, which is somewhat heuristic (but should work
|
|
even on networked filesystems with multiple writing machines).
|
|
|
|
----
|
|
|
|
Today's work was sponsored by Torbjørn Thorsen.
|