Re: [libvirt] Use flock() instead of fcntl()

Thank you for your quick response! Am Donnerstag, 25. Juli 2013, 10:31:40 schrieb Daniel P. Berrange: > On Thu, Jul 25, 2013 at 08:23:24AM +0000, David Weber wrote: > > Hi, > > > > we are interested in using virtlockd on an OCFS2 shared filesystem. > > We are now facing the problem that virtlockd uses fcntl() locks which > > aren't supported by OCFS2 with the o2cb cluster stack and we want > > to avoid using indirect leases. > > > > OCFS2 instead supports flock() which is quite similar to fcntl(). I > > attached a patch which makes libvirt use flock() *instead* of fcntl() > > and it seems to work. > > > > NFS on the contrast only supports fcntl() so it should be configurable > > which lock type to use. > > > > I'm not very experienced with locking, so would such a patch be > > acceptable or do you see possible problems with it? > > We definitely can't use flock() unconditionally like that, as it is > less widely supported than fcntl() locking and is known broken on > most network filesystems (flock() will only lock wrt the local node, > not network-wide). flock() locks are cluster aware in recent versions of OCFS2 and I would try to make it configurable which lock type to use. > I'm pretty surprised that you can fcntl() is not supported in ocfs2. > Are you really sure about that ? > > This mail message suggests it is supported > > https://oss.oracle.com/pipermail/ocfs2-users/2009-June/003572.html > > "Support for fcntl locking aka file-range locking aka posix locking is > provided by vfs for all file systems. However, that support is appropriate > only for local file systems. > > In ocfs2, we have added support for cluster-aware fcntl locking via > the userspace clustering framework that allows one to use ocfs2 with > different cluster-stacks." OCFS2 supports fcntl() only with the userspace cluster stacks (pacemaker and cman) which we want to avoid.

SUSE advises to use indirect leases which we also want to avoid: https://www.suse.com/documentation//sled11/book_kvm/?page=/documentation/... "virtlockd's default configuration does not allow you to lock disk files placed on a shared file system (for example NFS or OCFS2). Locking on these file systems requires you to specify a lockspace directory on the VM Host Server by setting" Although that's not completely correct because NFS supports fcntl()