From: "J. Bruce Fields" <bfields@fieldses.org>
To: NeilBrown <neilb@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>,
Chuck Lever <chuck.lever@oracle.com>,
linux-nfs@vger.kernel.org, Josef Bacik <josef@toxicpanda.com>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2] BTRFS/NFSD: provide more unique inode number for btrfs export
Date: Sun, 5 Sep 2021 12:07:19 -0400 [thread overview]
Message-ID: <20210905160719.GA20887@fieldses.org> (raw)
In-Reply-To: <163055605714.24419.381470460827658370@noble.neil.brown.name>
On Thu, Sep 02, 2021 at 02:14:17PM +1000, NeilBrown wrote:
> On Thu, 02 Sep 2021, J. Bruce Fields wrote:
> > I looked back through a couple threads to try to understand why we
> > couldn't do that (on new filesystems, with a mkfs option to choose new
> > or old behavior) and still don't understand. But the threads are long.
> >
> > There are objections to a new mount option (which seem obviously wrong;
> > this should be a persistent feature of the on-disk filesystem).
>
> I hadn't thought much (if at all) about a persistent filesystem feature
> flag. I'll try that now.
>
> There are two features of interest. One is completely unique inode
> numbers, the other is reporting different st_dev for different
> subvolumes. I think these need to be kept separate, though the second
> would depend on the first. They would be similar to my "inumbits" and
> "numdevs" mount options, though with less flexibility. I think that
> they would need strong semantics to be acceptable - "mostly unique"
> isn't really acceptable once we are changing the on-disk data.
I don't quite follow that.
Also the "on-disk data" here is literally just one more flag bit in some
superblock field, right?
> I believe that some code *knows* that the root of any btrfs subvolumes
> has inode number 256. systemd seems to use this. I have no idea what
> else might depend on inode numbers in some way.
Looking. Ugh, yes, there's abtrfs_might_be_subvol that takes a struct
stat and returns:
return S_ISDIR(st->st_mode) && st->st_ino == 256;
I wonder why it does that? Are there situations where all it has is a
file descriptor (so it can't easily compare st_dev with the parent?)
And if you NFS-export and wanted to answer the same question on the
client side, I wonder what you'd do.
--b.
next prev parent reply other threads:[~2021-09-05 16:07 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
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 [this message]
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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