On Thu, Jul 16, 2009 at 03:07:35PM -0700, Sage Weil wrote: > On Thu, 16 Jul 2009, Trond Myklebust wrote: > > On Thu, 2009-07-16 at 12:50 -0700, Sage Weil wrote: > > > On Thu, 16 Jul 2009, J. Bruce Fields wrote: > > > > On Wed, Jul 15, 2009 at 02:24:46PM -0700, Sage Weil wrote: > > > > > Basic NFS re-export support is included. This mostly works. However, > > > > > Ceph's MDS design precludes the ability to generate a (small) > > > > > filehandle that will be valid forever, so this is of limited utility. > > > > > > > > Is there any hope of fixing that? > > > > > > Yes, but it requires some additional ondisk metadata the MDS isn't > > > maintaining yet (a parent directory backpointer on file objects). > > > > > > The MDS changes will mean more random IO for rename intensive workloads, > > > but the backpointers would also be useful for rebuilding the directory > > > tree in the event of some catastrophic metadata loss or corruption. > > > (Currently they're only there for directories, not all files.) > > > > Note that a filehandle that contains parent directory information is > > still not one that is valid forever. It will change in the case of a > > cross-directory rename, and so isn't a filehandle in the NFSv2/v3 sense. > > Even in the NFSv4 case, it would have to be labelled as 'volatile'. > > Right. The parent directory information in the fh it used as a hint, but > can't be relied on because of the rename problem. That's exactly why the > Ceph MDS will need to be changed to maintain backpointers on all files, > not just directories. When that happens, reexporting via NFS will work > reliably. Until then, old and idle filehandles for renamed files will > eventually go stale. Maybe I should look again at the patch instead of continuing to ask, but.... I'm confused: how will having a backpointers from inodes to directories help do the filehandle-to-inode lookup? (If you can't look up the inode in the first place, what use is any pointer stored in that inode?) --b. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
