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[[!comment format=mdwn
username="ewen"
avatar="http://cdn.libravatar.org/avatar/605b2981cb52b4af268455dee7a4f64e"
subject="dtruss OS X 10.11 git annex on SMB mount"
date="2017-05-14T05:04:29Z"
content="""
A tar file with:
ewen@ashram:~/Desktop$ tar -tzf dtruss-git-annex-osx-smb-2017-05-14.tar.gz
dtruss-git-annex-osx-smb-2017-05-14/
dtruss-git-annex-osx-smb-2017-05-14/00-ga-test-smb-osx-symlinks-2017-05-14.script
dtruss-git-annex-osx-smb-2017-05-14/01-ga-test-smb-osx-symlinks-dtruss-git-annex-init-2017-05-14.txt
dtruss-git-annex-osx-smb-2017-05-14/02-ga-test-smb-osx-symlinks-dtruss-git-annex-sync-2017-05-14.txt
dtruss-git-annex-osx-smb-2017-05-14/03-ga-test-smb-osx-symlinks-dtruss-git-annex-get-all-2017-05-14.txt
dtruss-git-annex-osx-smb-2017-05-14/04-ga-test-smb-osx-symlinks-dtruss-git-annex-sync-other-way-2017-05-14.txt
dtruss-git-annex-osx-smb-2017-05-14/05-ga-test-smb-osx-symlinks-dtruss-git-annex-copy-to-smb-2017-05-14.txt
dtruss-git-annex-osx-smb-2017-05-14/dtruss-ga
ewen@ashram:~/Desktop$
is available at [dtruss-git-annex-osx-smb-2017-05-14.tar.gz](http://ewen.mcneill.gen.nz/temp/dtruss-git-annex-osx-smb-2017-05-14.tar.gz) (at least until I next tidy up the `/temp/` directory :-) ).
The script file is the output of \"`script ....`\" showing all the commands (including typos :-) ) run, except the `dtruss` ones themselves. The various `0n-ga-tst-smb-osx-symlinks-dtruss...` files contain the output of \"`sudo dtruss -af PID`\" where the `PID` was printed out by the script `dtruss-ga` that is included in the archive. `dtruss-ga` was used to enable running git-annex as non-root (to ensure that the SMB access wasn't altered by running as a different user), since `dtruss` itself can only run as root. The script is just:
ewen@ashram:~/Desktop$ cat dtruss-git-annex-osx-smb-2017-05-14/dtruss-ga
#! /bin/sh
# Allow dtruss of non-root git annex
#
# Based on hints at:
# http://sec.cs.ucl.ac.uk/users/smurdoch/blog/2015/08/fixing-slow-start-mc-on-osx.html
#---------------------------------------------------------------------------
echo \"Run: sudo dtruss -af -p $$\"
echo \"Then press enter\"
read
exec git annex \"$@\"
ewen@ashram:~/Desktop$
so basically \"print PID, wait for go ahead, run git annex command\".
From a quick glance through, it looks like:
7003/0x16c3126: 121576 14 11 write(0x12, \"PidLock {lockingPid = 7003, lockingHost = \\"ashram\\"}\0\", 0x33) = 51 0
7003/0x16c3126: 121775 3350 191 close(0x12) = 0 0
7003/0x16c3126: 121792 10 6 stat64(\"/Volumes/music/ga-test/.git/annex/locktmp16807282475249\0\", 0x200004940, 0x33) = 0 0
7003/0x16c3126: 122041 2341 235 link(\"/Volumes/music/ga-test/.git/annex/locktmp16807282475249\0\", \"/Volumes/music/ga-test/.git/annex/locktmp16807282475249.lnk\0\") = -1 Err#45
7003/0x16c3126: 122115 885 49 unlink(\"/Volumes/music/ga-test/.git/annex/locktmp16807282475249.lnk\0\", 0x200004D80, 0x33) = -1 Err#2
(in `03-...`, the first `get`) probably isn't helping -- that's trying to do a *hardlink* on a SMB file system, and appearing to give up when it fails... (`/Volumes/music` is the SMB mount I was using for testing).
Also since I didn't realise until after the `script` file/`tar` file were made, there *is* an `annex/pidlock` file:
ewen@ashram:~$ ls -l /Volumes/music/ga-test/.git/annex/pidlock
-rwx------ 1 ewen staff 51 14 May 16:25 /Volumes/music/ga-test/.git/annex/pidlock
ewen@ashram:~$ cat /Volumes/music/ga-test/.git/annex/pidlock
PidLock {lockingPid = 7143, lockingHost = \"ashram\"}ewen@ashram:~$
ewen@ashram:~$
created within the SMB `git-annex`, which looks vaguely sensible. And FTR, there is *not* one in the HFS (local OS X) `git-annex`:
ewen@ashram:~$ ls -l /var/tmp/ga-test/.git/annex/pidlock
ls: /var/tmp/ga-test/.git/annex/pidlock: No such file or directory
ewen@ashram:~$
so it definitely seems to *try* to do pidlocking on the SMB mount on transfers, but it looks like maybe it's also trying to do something *not* supported.
Looking through the OS X `open(2)` manpage, it appears that:
O_EXCL error if O_CREAT and the file exists
[...]
O_EXLOCK atomically obtain an exclusive lock
might be plausible non-hardlink locking primitives that'd work better than nothing. The manpage also says:
When opening a file, a lock with flock(2) semantics can be obtained by
setting O_SHLOCK for a shared lock, or O_EXLOCK for an exclusive lock.
If creating a file with O_CREAT, the request for the lock will never fail
(provided that the underlying filesystem supports locking).
so maybe that's something to work with? (SMB as a protocol supports All Kinds Of Locking (tm), and hopefully the OS X SMB file system driver would also translate O_EXLOCK, etc, through to those...)
Hope that's of some help.
Ewen
PS: Yes, I do plan to try to install the stand alone x86-64 git-annex on my Synology when I get a spare few hours to sort out all the details. It seems like it would be the most robust solution for my specific problem. But generalised SMB support could also be useful, even if it was \"user needs to be careful about running commands in parallel as there are races\".
"""]]
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