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Date:   Thu, 15 Jul 2021 17:45:14 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Josef Bacik <josef@toxicpanda.com>
Cc:     NeilBrown <neilb@suse.de>,
        "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.
Message-ID: <YPBmGknHpFb06fnD@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>
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On Thu, Jul 15, 2021 at 10:09:37AM -0400, Josef Bacik wrote:
> I'm going to restate what I think the problem is you're having just so I'm
> sure we're on the same page.
> 
> 1. We export a btrfs volume via nfsd that has multiple subvolumes.
> 2. We run find, and when we stat a file, nfsd doesn't send along our bogus
> st_dev, it sends it's own thing (I assume?).  This confuses du/find because
> you get the same inode number with different parents.
> 
> Is this correct?  If that's the case then it' be relatively straightforward
> to add another callback into export_operations to grab this fsid right?
> Hell we could simply return the objectid of the root since that's unique
> across the entire file system.  We already do our magic FH encoding to make
> sure we keep all this straight for NFS, another callback to give that info
> isn't going to kill us.  Thanks,

Hell no.  btrfs is broken plain and simple, and we've been arguing about
this for years without progress.  btrfs needs to stop claiming different
st_dev inside the same mount, otherwise hell is going to break lose left
right and center, and this is just one of the many cases where it does.