From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:31385 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751670Ab1KUQgM (ORCPT ); Mon, 21 Nov 2011 11:36:12 -0500 Date: Mon, 21 Nov 2011 17:35:43 +0100 From: Karel Zak To: Mike Frysinger Cc: util-linux@vger.kernel.org, Michal Kubecek , Petr Uzel Subject: Re: flock in 2.20.1 can no longer lock the file it will execute Message-ID: <20111121163543.GU7916@nb.net.home> References: <201111140123.39789.vapier@gentoo.org> <20111116131321.GN7916@nb.net.home> <201111161025.47605.vapier@gentoo.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <201111161025.47605.vapier@gentoo.org> Sender: util-linux-owner@vger.kernel.org List-ID: On Wed, Nov 16, 2011 at 10:25:46AM -0500, Mike Frysinger wrote: > 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 ? yes, EIO > 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 ... Good idea, implemented and tested (git pull to get the change). It seems it works with your example as well as with NFSv4. Karel -- Karel Zak http://karelzak.blogspot.com