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Improve ssh socket cleanup code to skip over the cruft that NFS sometimes puts in a directory when a file is being deleted.

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Joey Hess 2016-10-26 13:16:41 -04:00
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[[!comment format=mdwn
username="joey"
subject="""comment 13"""
date="2016-10-26T16:34:38Z"
content="""
Looking at the strace finally...
Here's git-annex creating the dummy posix lock file, soon after
the ssh socket is removed. (I think that's ssh removing the socket before,
but the jumble of strace output is hard to follow here.)
2456732 unlink(".git/annex/ssh/smaug" <unfinished ...>
...
2456732 open(".git/annex/ssh/.nfs00000000099d85d000000002.lock", O_RDONLY|O_CREAT, 0666 <unfinished ...>
And later ssh is told to stop using a related socket:
2456815 execve("/mnt/btrfs/scrap/datalad/test_nfs/git-annex.linux/bin/ssh", ["ssh", "-O", "stop", "-S", ".nfs00000000099d85d000000002", "-o", "ControlMaster=auto", "-o", "ControlPersist=yes", "localhost"], [/* 98 vars */] <unfinished ...>
Which it seems does not exist by then:
2456815 connect(3, {sa_family=AF_LOCAL, sun_path=".nfs00000000099d85d000000002"}, 31) = -1 ENOENT (No such file or directory)
2456732 unlink(".git/annex/ssh/.nfs00000000099d85d000000002") = -1 ENOENT (No such file or directory)
Seems like this would have to be `sshCleanup` running, and `enumSocketFiles`
seeing ".nfs00000000099d85d000000002" existing at that point due
probably to the ssh/smaug socket being in the process of being
removed.
So, it assumes it's a socket file and tries to clean it up, creating
the dummy posix lock file. And posix lock files don't get deleted
(it's impossible to do so in a race-free way), so this results in more
and more `.nfs*.lock` files.
Need to find a way to prevent `enumSocketFiles` from listing these
files. Seems that ".nfs00000000099d85d000000002" is probably the deleted
form of the "smaug" socket, so it really is a socket file, so checking
if a file is a socket won't help. Of course it could
explicitly filter out ".nfs" prefixed files. That could be a case of
kicking the can down the road, since NFS could always choose to use
another name for these files.
Hmm.. Before a ssh socket file gets created, git-annex always locks the
associated lock file. And as noted, the posix lock file is never
removed. (On Windows the lock file is also created and never deleted.)
So, if $file does not have an associated $file.lock
then $file must not be a ssh socket, and `enumSocketFiles` can skip it.
I've added that check. Unable to test it because the NFS mount has
been lost in the intervening time. @yoh can you test this fixed it?
"""]]