The `cabal install git-annex` doesn't install the man pages, and the
Makefile only installed the man pages as part of a full build/install.
So, I factored out the documentation parts of the Makefile.
Anything that tries to open the file for write, or delete the file,
or replace it with something else, will not affect the add.
Only if a process has the file open for write before add starts
can it still change it while (or after) it's added to the annex.
(fsck will catch this later of course)
Uses a MVar again, as there seems no other way to thread the state through
inotify events.
This is a rather unsatisfactory result. I had wanted to run them in
the same monad so that the git queue could be used to coleasce git commands
and speed things up. But, that led to fragility: If several files are
added, and one is removed before queue flush, git add will fail to add
any of them. So, the queue is still explicitly flushed after each add for
now.
TODO: Investigate using git add --ignore-errors. This would need to be done
in Command.Add. And, git add still exits nonzero with it, so would need
to avoid crashing on queue flush.
This allows the queue to be used in a single process for multiple possibly
conflicting commands, like add and rm, without running them out of order.
This assumes that running the same git subcommand with different parameters
cannot itself conflict.
When a new file is annexed, a deletion event occurs when it's moved away
to be replaced by a symlink. Most of the time, there is no problimatic
race, because the same thread runs the add event as the deletion event.
So, once the symlink is in place, the deletion code won't run at all,
due to existing checks that a deleted file is really gone.
But there is a race at startup, as then the inotify thread is running
at the same time as the main thread, which does the initial tree walking
and annexing. It would be possible for the deletion inotify to run
in a perfect race with the addition, and remove the newly added symlink
from the git cache.
To solve this race, added event serialization via a MVar. We putMVar
before running each event, which blocks if an event is already running.
And when an event finishes (or crashes!), we takeMVar to free the lock.
Also, make rm -rf not spew warnings by passing --ignore-unmatch when
deleting directories.
