Re: Debugging fcntl() file locks

[Bernd Petrovitsch <bernd@petrovitsch.priv.at>]

Hi!

On Don, 2010-05-27 at 08:34 -0400, Trond Myklebust wrote:
> On Thu, 2010-05-27 at 12:11 +0200, Bernd Petrovitsch wrote:
[...]
> > How can I debug fcntl() file locks on a NFSv3-client?
> > The server side is a NetApp-Box (no details at hand but I can ask).
> > The client side are stock-RHEL5.3/CentOS-5.3 kernels - 2.6.18-92.el5.
> > 
> > The file system in question is mounted on 2 clients. flock() on a file
> > succeeds but fcntl() fails with EAGAIN. From what I found in the
> > Internet and manual pages, this means that someone else already locked
> > that file (- the file is successfully open()ed read/write so it can't be
> > "your are not allowed to write-lock the file").
> > But how do I find out on which host and which process?
> > 
> > strace shows:
> > ----  snip  ----
> > open("/... secret ...", O_RDWR) = 3
> > ioctl(3, SNDCTL_TMR_TIMEBASE or TCGETS, 0x7fff7925b400) = -1 ENOTTY (Inappropriate ioctl for device)
> > lseek(3, 0, SEEK_CUR)                   = 0
> > fstat(3, {st_mode=S_IFREG|0600, st_size=935, ...}) = 0
> > fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
> > flock(3, LOCK_EX|LOCK_NB)               = 0
> > fcntl(3, F_SETLK, {type=F_WRLCK, whence=SEEK_SET, start=0, len=0}) = -1 EAGAIN (Resource temporarily unavailable)
> > ----  snip  ---- 
> > [ This is a perl script using CPAN modules at the top. ]
[...]
> The Linux NFS client does not allow you to lock a file using both
> flock() and POSIX locks. You should choose one or the other locking
> scheme. If you remove the flock() line above, then the POSIX lock will
> likely succeed.

Thanks.
Does flock() work on NFS these days on NFS?
Historically that was not the case IIRC.

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
                     LUGA : http://www.luga.at