Re: udev and devfs - The final word

Andreas Dilger
2003-12-31T23:48:44Z

On Dec 31, 2003 22:55 +0000, viro@parcelfarce.linux.theplanet.co.uk wrote:
> h) nfsd uses device number as a substitute for export ID if said
> ID is not given explicitly. That, BTW, is a big problem for crackpipe
> dreams about random device numbers - export ID _must_ be stable across
> reboots.

We had a problem with this and Lustre, when we NFS export it. Lustre is
already a network filesystem so we don't have a device number. I had a
discussion with Neil Brown about this and suggested that we allow NFS to
get a _real_ stable export ID from the filesystem (e.g. superblock UUID
or similar) instead of the device number hackery which only has a vague
relationship to stable.

We implemented it for Lustre with a filesystem option FS_NFSEXP_FSID
that tells nfsd it can export such a filesystem in the absence of
FS_REQUIRES_DEV and then put our export ID into sb->s_dev (although I'd
prefer something slightly cleaner than that).

Cheers, Andreas
--
Andreas Dilger