On Wednesday 16 November 2011 08:13:21 Karel Zak wrote: > On Mon, Nov 14, 2011 at 01:23:38AM -0500, Mike Frysinger wrote: > > i've been using a trick with flock to add locking to all of my shell > > scripts. > > > > basically, i take a lock on the shell script itself: > > flock -eon ./test.sh ./test.sh > > > > with <=util-linux-2.20, this has worked fine. but starting with 2.20.1, > > i now > > > > get -ETXTBSY (on ext4, but i doubt that matters): > > $ echo '#!/bin/sh' > test.sh > > $ chmod a+rx test.sh > > $ ./flock -eon ./test.sh ./test.sh > > ./flock: ./test.sh: Text file busy > > > > the only commit made to flock.c between 2.20 and 2.20.1 is this: > > commit 75aaee08f06b92d119ed827c53d1af5474eb16ff > > flock: make flock(1) work on NFSv4 > > > > and indeed, reverting that made my life happy again. reading the small > > patch shows the obvious flaw: you can't open a file for O_RDWR and > > attempt to execute it at the same time. > > Hmm... maybe we can add a new --read-write command line option for > NFS guys rather than be smart with access(). The regression is > unacceptable. i wonder what happens if you attempt to take a read-only lock on nfs. do you get back an error ? or does it fail silently at runtime in the nfs layers ? if the former, one solution might be to open the file, attempt to grab the lock, and if the flock() fails, retry the whole thing but with O_RDWR instead. int rw_flags = O_RDONLY; ... retry: ... current open logic which uses new rw_flags var ... ... if flock fails, and rw_flags == O_RDONLY, then set rw_flags to O_RDWR and jump back to retry ... -mike
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