svn commit: r212216 - head/sys/fs/nfsclient

[Rick Macklem]

> On Saturday 04 September 2010 08:10:18 pm Rick Macklem wrote:
> > Author: rmacklem
> > Date: Sun Sep 5 00:10:18 2010
> > New Revision: 212216
> > URL: http://svn.freebsd.org/changeset/base/212216
> >
> > Log:
> >   Disable use of the NLM in the experimental NFS client, since
> >   it will crash the kernel because it uses the nfsmount and
> >   nfsnode structures of the regular NFS client.
> 
> Hmm, perhaps we could provide new VFS and/or VOP methods for NLM to
> use
> instead of reaching inside of those structures directly? I think we
> really
> want to support NLM on the new NFS client as many folks want working
> NFS
> locking.
> 
Actually, passing the extra information in would just be a matter of
adding extra arguments to nlm_advlock(), which is always called by
the nfs clients and never as a VOP_ADVLOCK() call. This would be
slightly ugly, but not that messy and doesn't require VOP changes.

Where it gets ugly is that nlm_advlock() saves "struct nfsmount *nmp"
in a structure called "struct nlm_feedback_arg nf" and uses that
later to fiddle with fields in *nmp in nlm_down() and nlm_up()
called from nlm_feedback(), which is called asynchronously from the
krpc layer. (This does need to be fixed someday, since it is badly
broken for forced dismounts.)

If you look at nlm_down() and nlm_up(), it uses the *nmp to avoid
doing a vfs_event_signal() call multiple times for a mount point.
Since I don't understand what vfs_event_signal(fsid, VQ_NOTRESPLOCK, 0);
actually does, I don't know if multiple calls would be a serious
problem?

I suppose I could add a global/malloc'd list of structures to
nlm_advlock() { one for each *nmp } to keep this flag, but then
I'm not sure I'd know when to get rid of elements in the list
(because I wouldn't know when a mount point is dismounted?).

I looked at this some time ago, when kib@ was trying to fix forced
dismounts, but never got it fixed then. If this ugly bit is
fixed, I think adding extra args to nlm_advlock() would make it
work for both clients concurrently.

If anyone can help with the ugly part, please pass along any
suggestions.

Thanks, rick
ps: and I don't want to "own" the nlm:-)