Re: nfs-utils 1.1.2 + knfsd 2.6.27 (.5) breaks fsid= option

["J. Bruce Fields" <bfields@fieldses.org>]

On Sun, Nov 16, 2008 at 09:29:35PM +0100, Frank van Maarseveen wrote:
> On Sun, Nov 16, 2008 at 03:02:11PM -0500, J. Bruce Fields wrote:
> > On Wed, Nov 12, 2008 at 08:48:47AM -0500, Steve Dickson wrote:
> > > Frank van Maarseveen wrote:
> > > > Tested on Debian lenny with nfs-kernel-server 1:1.1.2-6lenny1 and a
> > > > 2.6.27.5 kernel. /etc/exports says:
> > > > 
> > > > 	/mp @general(rw,sync,no_root_squash,no_subtree_check,mp,fsid=2886795869)
> > > > 
> > > > After actually using it /proc/fs/nfsd/exports says:
> > > > 
> > > > 	/mp @general(rw,no_root_squash,sync,wdelay,no_subtree_check,fsid=-1408171427,uuid=db4387a6:bed949d0:8f5ef6a2:6a0c
> > > > 
> > > > (yes, 2886795869 == (ulong)-1408171427)
> > > > However, file handles over the wire now seem to have fsid_type=6
> > > > (FSID_UUID16) instead of 1 (FSID_NUM) due to this.
> > > 
> > > This is a known problem... The kernel checks UUIDs before FSIDS which cause
> > > FSIDS to be ignored. There are two outstanding proposals to fix this problem.
> > >    1) Move two lines in the kernel so FSIDs are checked before UUIDS
> > >    2) Change mountd to only send down  the FSID or the UUID but
> > >       not both as it does today.
> > >  
> > > Neither proposal has been accepted... yet...
> > 
> > I'd have a mild preference for the 2nd, but I'd first like to understand
> > why the new behavior is a problem for Frank.
> 
> I'm using a patch originally developed by Wendy Cheng for a per-fsid
> grace period. It could be triggered by:
> 
> 	echo fsid >/proc/fs/nfsd/nlm_grace_fsid
> 
> where the mentioned fsid is the same as in /etc/exports. I'm not
> particularly fond of using fsids for this and AFAIK a similar patch for
> per-mountpoint grace period is underway. Correct?

Yes.  In the meantime it shouldn't be hard to modify Wendy's patch to
use a filename instead of an fsid--see
fs/nfsd/nfsctl.c:failover_unlock_fs() for an example of an existing nfsd
file that takes a pathname.

But that shouldn't even be necessary--the fsid is still stored with the
filesystem internally, so Wendy's code should still be able to look up
exports using it.

--b.