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List:       linux-kernel
Subject:    Re: udev and devfs - The final word
From:       Andreas Dilger <adilger () clusterfs ! com>
Date:       2003-12-31 23:48:24
Message-ID: 20031231164824.I6144 () schatzie ! adilger ! int
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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
http://sourceforge.net/projects/ext2resize/
http://www-mddsp.enel.ucalgary.ca/People/adilger/

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