[LTP] [PATCH 1/5] fcntl40: test for owner values on classic posix lock

[Alexander Aring]

Hi,

On Sun, Jul 2, 2023 at 3:18 PM Petr Vorel <pvorel@suse.cz> wrote:
>
> Hi Alex,
>
> ...
> > > > + * [Description]
> > > > + * Tests gfs2 dlm posix op queue handling in the kernel.
> > > > + * It is recommended to run watch -n 0.1 "dlm_tool plocks $LS"
> > > > + * aside to monitor dlm plock handling.
> > > > + *
> > > > + * [How to use it]
> > > > + * Call it with TMPDIR=/mnt ./fcntl40 where TMPDIR is a gfs2 mountpoint.
> > > I wonder if we could check for GFS2_MAGIC (we'd need to add it to
> > > include/tst_fs.h => 0x01161970) and quit the test with tst_brk(TCONF) if TMPDIR
> > > is not on gfs2.
>
> > > ATM we don't have any helper in struct tst_test, which would do it.
>
>
> > I will mention that gfs2 is only an example here. It becomes
> > interesting when a file system implements its own .lock() callback OR
> > if somebody wants to test file system core, when a filesystem does not
> > implement its own .lock().
>
> I see .lock is implemented in 9p, afs, ceph, cifs, ocfs2, orangefs, even NFS.
> "file system core": do you mean VFS? Because that would be more usable than the
> filesystems above (which are quite exotic).
>

It depends here what they are doing in .lock() - If they just call
locks_lock_file_wait() or similar helpers depending on the call, then
they don't do much different than what vfs is doing.
In case of gfs2/ocfs it is very special, it redirects their calls to
DLM and DLM has its own whole posix implementation behind it. We only
call locks_lock_file_wait() to keep the Linux bookkeeping in
/proc/locks.

What I am doing here is mostly trusting the Linux implementation and
comparing results from e.g. tmpfs with GFS2 and I found issues.

For now I trust the Linux implementation and check if we have a
different result here. I need to be very careful here because
GFS2/OCFS2 are cluster filesystems and the fcntl() interface was never
made for cluster filesystems. However I currently only test "one node"
locking and this should deliver the same results as tmpfs, etc.

- Alex