On Tue, 12 Oct 2010 13:57:53 -0400 Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > On Oct 12, 2010, at 1:04 PM, Trond Myklebust wrote: > > > On Tue, 2010-10-12 at 12:29 -0400, Chuck Lever wrote: > >> I've been looking at a bug where "mount.nfs -o remount" wipes all the mount options for that mount out of /etc/mtab, thereby making umounting break. > >> > >> This is a tough nut to crack in user space... Not even utils-linux-ng seems to get mtab option rewriting correct in this case. > >> > >> Jeff suggested a few weeks ago that we should just chuck user space umount and go with a kernel umount implementation. I'm beginning to think that is a good strategy, even though a UMNT request is advisory. > >> > >> + Only the kernel knows when the last instance of a shared mount point is gone -- only then should a UMNT be sent to the server > >> > >> + The kernel might do a delayed lazy UMNT. It would avoid sending a UMNT until the client is actually done using the export. Today we just don't send UMNT at all in this case > >> > >> + The kernel preserves the original mount options in an internal data structure rather than in /etc/mtab, even after a remount. This eliminates the NFS requirement for /etc/mtab -- one step closer to getting rid of it > >> > >> + The kernel already handles umounts for under-the-cover NFSv4 mounts, right? > >> > >> + The kernel is the authority on what is an NFSv4 mount point, so it knows exactly what kind of umount to do every time (send a UMNT or not) > >> > >> + There is already a UMNT client in the kernel, used when the kernel's MNT request fails such that a UMNT is needed > >> > >> Thoughts, comments? > >> > > > > UMNT is an advisory thing. If it causes problems, then lets just drop > > it. > > Out of interest, what would that look like? Would we rip out all code from nfsumount.c and network.c that handles UMNT calls? > I think the part that causes problems is having userspace do this. In theory, if the kernel were in charge of sending the UMNT, then it's not really a problem since it knows when to do it. If we have code that sends a UMNT already, why not do a best-effort UMNT call from the kernel when we tear down the sb? Either way, eliminating umount.nfs would be nice... -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
