git merge watch_

My cursor has been mentally poised here all day, but I've been reluctant to merge watch into master. It seems solid, but is it correct? I was able to think up a lot of races it'd be subject to, and deal with them, but did I find them all?

Perhaps I need to do some automated fuzz testing to reassure myself. I looked into using genbackupdata to that end. It's not quite what I need, but could be moved in that direction. Or I could write my own fuzz tester, but it seems better to use someone else's, because a) laziness and b) they're less likely to have the same blind spots I do.

My reluctance to merge isn't helped by the known bugs with files that are either already open before git annex watch starts, or are opened by two processes at once, and confuse it into annexing the still-open file when one process closes it.

I've been thinking about just running lsof on every file as it's being annexed to check for that, but in the end, lsof is too slow. Since its check involves trawling through all of /proc, it takes it a good half a second to check a file, and adding 25 seconds to the time it takes to process 100 files is just not acceptable.

But an option that could work is to run lsof after a bunch of new files have been annexed. It can check a lot of files nearly as fast as a single one. In the rare case that an annexed file is indeed still open, it could be moved back out of the annex. Then when its remaining writer finally closes it, another inotify event would re-annex it.