On Tue, 2010-12-07 at 17:51 +0100, Christoph Hellwig wrote: > On Sat, Dec 04, 2010 at 09:27:56AM +1100, Dave Chinner wrote: > > A property of NFS fileshandles is that they must be stable across > > server reboots. Is this anon dev_t used as part of the NFS > > filehandle and if so how can you guarantee that it is stable? > > It's just as stable as a real dev_t in the times of hotplug and udev. > As long as you don't touch anything including not upgrading the kernel > it's remain stable, otherwise it will break. That's why modern > nfs-utils default to using the uuid-based filehandle schemes instead of > the dev_t based ones. At least that's what I told - I really hope it's > using the real UUIDs from the filesystem and not the horrible fsid hack > that was once added - for some filesystems like XFS that field does not > actually have any relation to the UUID historically. And while we could > have changed that it's too late now that nfs was hacked into abusing > that field. IIRC, NFS uses the full true uuid for NFSv3 and NFSv4 filehandles, but they won't fit into the NFSv2 32-byte filehandles, so there is an '8-byte fsid' and '4-byte fsid + inode number' workaround for that... See the mk_fsid() helper in fs/nfsd/nfsfh.h Cheers Trond -- Trond Myklebust Linux NFS client maintainer NetApp Trond.Myklebust@xxxxxxxxxx www.netapp.com -- 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
