Re: [PATCH] file-posix: detect the lock using the real file

[Kevin Wolf]

Am 09.12.2020 um 10:33 hat Daniel P. Berrangé geschrieben:
> On Tue, Dec 08, 2020 at 03:38:22PM +0100, Kevin Wolf wrote:
> > Am 08.12.2020 um 13:59 hat Li Feng geschrieben:
> > > This patch addresses this issue:
> > > When accessing a volume on an NFS filesystem without supporting the file 
> > > lock,
> > > tools, like qemu-img, will complain "Failed to lock byte 100".
> > > 
> > > In the original code, the qemu_has_ofd_lock will test the lock on the
> > > "/dev/null" pseudo-file. Actually, the file.locking is per-drive property,
> > > which depends on the underlay filesystem.
> > > 
> > > In this patch, make the 'qemu_has_ofd_lock' with a filename be more 
> > > generic
> > > and reasonable.
> > > 
> > > Signed-off-by: Li Feng <fengli@smartx.com>
> > 
> > Do you know any way how I could configure either the NFS server or the
> > NFS client such that locking would fail? For any patch related to this,
> > it would be good if I could even test the scenario.
> 
> One could write a qtest that uses an LD_PRELOAD to replace the standard
> glibc fcntl() function with one that returns an error for locking commands.

Sounds a bit ugly, but for regression testing it could make sense.

However, part of the testing would be to verify that we our checks
actually match the kernel code, which this approach couldn't solve.

Kevin