From: Christoph Hellwig <hch@infradead.org>
To: NeilBrown <neilb@suse.de>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
Chuck Lever <chuck.lever@oracle.com>,
linux-nfs@vger.kernel.org, Josef Bacik <josef@toxicpanda.com>
Subject: Re: [PATCH v2] BTRFS/NFSD: provide more unique inode number for btrfs export
Date: Fri, 27 Aug 2021 17:20:47 +0100 [thread overview]
Message-ID: <YSkQ31UTVDtBavOO@infradead.org> (raw)
In-Reply-To: <162995778427.7591.11743795294299207756@noble.neil.brown.name>
On Thu, Aug 26, 2021 at 04:03:04PM +1000, NeilBrown wrote:
>
> [[ Hi Bruce and Chuck,
> I've rebased this patch on the earlier patch I sent which allows
> me to use the name "fh_flags". I've also added a missing #include.
> I've added the 'Acked-by' which Joesf provided earlier for the
> btrfs-part. I don't have an 'ack' for the stat.h part, but no-one
> has complained wither.
> I think it is as ready as it can be, and am keen to know what you
> think.
> I'm not *very* keen on testing s_magic in nfsd code (though we
> already have a couple of such tests in nfs3proc.c), but it does have
> the advantage of ensuring that no other filesystem can use this
> functionality without landing a patch in fs/nfsd/.
>
> Thanks for any review that you can provide,
> NeilBrown
> ]]
>
> BTRFS does not provide unique inode numbers across a filesystem.
> It only provides unique inode numbers within a subvolume and
> uses synthetic device numbers for different subvolumes to ensure
> uniqueness for device+inode.
>
> nfsd cannot use these varying synthetic device numbers. If nfsd were to
> synthesise different stable filesystem ids to give to the client, that
> would cause subvolumes to appear in the mount table on the client, even
> though they don't appear in the mount table on the server. Also, NFSv3
> doesn't support changing the filesystem id without a new explicit mount
> on the client (this is partially supported in practice, but violates the
> protocol specification and has problems in some edge cases).
>
> So currently, the roots of all subvolumes report the same inode number
> in the same filesystem to NFS clients and tools like 'find' notice that
> a directory has the same identity as an ancestor, and so refuse to
> enter that directory.
>
> This patch allows btrfs (or any filesystem) to provide a 64bit number
> that can be xored with the inode number to make the number more unique.
> Rather than the client being certain to see duplicates, with this patch
> it is possible but extremely rare.
Yikes. Please don't do something like this that will eventually
cause collisions.
next prev parent reply other threads:[~2021-08-27 16:21 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-26 4:28 [PATCH] NFSD: drop support for ancient file-handles NeilBrown
2021-08-26 6:03 ` [PATCH v2] BTRFS/NFSD: provide more unique inode number for btrfs export NeilBrown
2021-08-26 20:19 ` J. Bruce Fields
2021-08-26 22:10 ` NeilBrown
2021-08-27 14:53 ` Frank Filz
2021-08-27 22:57 ` NeilBrown
2021-08-27 23:46 ` Frank Filz
2021-08-27 23:55 ` NeilBrown
2021-08-28 2:21 ` Frank Filz
2021-08-27 18:32 ` J. Bruce Fields
2021-08-27 23:01 ` NeilBrown
2021-08-27 16:20 ` Christoph Hellwig [this message]
2021-08-27 23:05 ` NeilBrown
2021-08-28 7:09 ` Christoph Hellwig
2021-08-31 4:59 ` NeilBrown
2021-09-01 7:20 ` Christoph Hellwig
2021-09-01 15:22 ` J. Bruce Fields
2021-09-02 4:14 ` NeilBrown
2021-09-05 16:07 ` J. Bruce Fields
2021-09-06 1:29 ` NeilBrown
2021-09-11 14:12 ` Amir Goldstein
2021-09-13 0:43 ` NeilBrown
2021-09-13 10:04 ` Amir Goldstein
2021-09-13 22:59 ` NeilBrown
2021-09-14 5:45 ` Amir Goldstein
2021-09-20 22:09 ` NeilBrown
2021-09-02 7:11 ` Christoph Hellwig
2021-09-02 4:06 ` NeilBrown
2021-09-02 7:16 ` Christoph Hellwig
2021-09-02 7:53 ` Miklos Szeredi
2021-09-02 14:16 ` Frank Filz
2021-09-02 23:02 ` NeilBrown
2021-08-26 14:10 ` [PATCH] NFSD: drop support for ancient file-handles Chuck Lever III
2021-08-26 21:38 ` NeilBrown
2021-08-26 14:51 ` J. Bruce Fields
2021-08-26 21:41 ` NeilBrown
2021-08-27 15:15 ` Christoph Hellwig
2021-08-27 23:24 ` NeilBrown
2021-08-31 4:41 ` [PATCH 1/2 v2] NFSD: drop support for ancient filehandles NeilBrown
2021-08-31 4:42 ` [PATCH 2/2] NFSD: simplify struct nfsfh NeilBrown
2021-09-01 7:44 ` Christoph Hellwig
2021-09-01 7:44 ` [PATCH 1/2 v2] NFSD: drop support for ancient filehandles Christoph Hellwig
2021-09-01 14:21 ` Chuck Lever III
2021-09-02 1:14 ` [PATCH 1/3 v3] NFSD: move filehandle format declarations out of "uapi" NeilBrown
2021-09-02 1:15 ` [PATCH 2/3 v3] NFSD: drop support for ancient filehandles NeilBrown
2021-09-02 1:16 ` [PATCH 3/3 v3] NFSD: simplify struct nfsfh NeilBrown
2021-09-02 7:22 ` [PATCH 2/3 v3] NFSD: drop support for ancient filehandles Christoph Hellwig
2021-09-02 7:21 ` [PATCH 1/3 v3] NFSD: move filehandle format declarations out of "uapi" Christoph Hellwig
2021-09-23 21:21 ` Bruce Fields
2021-09-25 4:21 ` NeilBrown
-- strict thread matches above, loose matches on Subject: below --
2021-07-27 22:37 [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly NeilBrown
2021-08-13 1:45 ` [PATCH] VFS/BTRFS/NFSD: provide more unique inode number for btrfs export NeilBrown
2021-08-15 7:39 ` Goffredo Baroncelli
2021-08-15 19:35 ` Roman Mamedov
2021-08-15 22:17 ` NeilBrown
2021-08-23 4:05 ` [PATCH v2] BTRFS/NFSD: " NeilBrown
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