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From:   "NeilBrown" <neilb@suse.de>
To:     "Christoph Hellwig" <hch@infradead.org>
Cc:     "Josef Bacik" <josef@toxicpanda.com>,
        "Christoph Hellwig" <hch@infradead.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        "Chuck Lever" <chuck.lever@oracle.com>, "Chris Mason" <clm@fb.com>,
        "David Sterba" <dsterba@suse.com>, linux-nfs@vger.kernel.org,
        "Wang Yugui" <wangyugui@e16-tech.com>,
        "Ulli Horlacher" <framstag@rus.uni-stuttgart.de>,
        linux-btrfs@vger.kernel.org
Subject: Re: [PATCH/RFC] NFSD: handle BTRFS subvolumes better.
In-reply-to: <YPVC/w4kw3y/14oF@infradead.org>
References: <20210613115313.BC59.409509F4@e16-tech.com>,
 <20210310074620.GA2158@tik.uni-stuttgart.de>,
 <162632387205.13764.6196748476850020429@noble.neil.brown.name>,
 <edd94b15-90df-c540-b9aa-8eac89b6713b@toxicpanda.com>,
 <YPBmGknHpFb06fnD@infradead.org>,
 <28bb883d-8d14-f11a-b37f-d8e71118f87f@toxicpanda.com>,
 <YPBvUfCNmv0ElBpo@infradead.org>,
 <e1d9caad-e4c7-09d4-b145-5397b24e1cc7@toxicpanda.com>,
 <YPVC/w4kw3y/14oF@infradead.org>
Date:   Tue, 20 Jul 2021 09:54:44 +1000
Message-id: <162673888433.4136.7451392112850411713@noble.neil.brown.name>
Precedence: bulk

On Mon, 19 Jul 2021, Christoph Hellwig wrote:
> On Thu, Jul 15, 2021 at 02:01:11PM -0400, Josef Bacik wrote:
> > This is not a workable solution.  It's not a matter of simply tying into
> > existing infrastructure, we'd have to completely rework how the VFS deals
> > with this stuff in order to be reasonable.  And when I brought this up to=
 Al
> > he told me I was insane and we absolutely had to have a different SB for
> > every vfsmount, which means we can't use vfsmount for this, which means we
> > don't have any other options.  Thanks,
>=20
> Then fix the problem another way.  The problem is known, old and keeps
> breaking stuff.  Don't paper over it, fix it.=20

Do you have any pointers to other breakage caused by this particular
behaviour of btrfs? It would to have all requirements clearly on the
table while designing a solution.

Thanks,
NeilBrown