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Date:   Wed, 3 Mar 2021 08:01:03 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>, linux-fsdevel@vger.kernel.org,
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Subject: Re: [PATCH v6 39/40] xfs: support idmapped mounts
Message-ID: <20210303070103.GA7866@lst.de>
References: <20210121131959.646623-1-christian.brauner@ubuntu.com> <20210121131959.646623-40-christian.brauner@ubuntu.com> <20210301200520.GK7272@magnolia>
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User-Agent: Mutt/1.5.17 (2007-11-01)
Precedence: bulk

On Mon, Mar 01, 2021 at 12:05:20PM -0800, Darrick J. Wong wrote:
> > +	if (breq->mnt_userns != &init_user_ns) {
> > +		xfs_warn_ratelimited(breq->mp,
> > +			"bulkstat not supported inside of idmapped mounts.");
> > +		return -EINVAL;
> 
> Shouldn't this be -EPERM?
> 
> Or -EOPNOTSUPP?

-EINVAL is what we return for all our nor suppored ioctls, so I think it
is the right choice here, and should generally trigger the right
fallbacks.

> Also, I'm not sure why bulkstat won't work in an idmapped mount but
> bulkstat_single does?  You can use the singleton version to stat inodes
> that aren't inside the submount.

Looking at it again I think we should fail BULKSTAT_SINGLE as well.
I had somehow assumed BULKSTAT_SINGLE would operate on the inode of
the open file, in which case it would be fine.  But it doesn't so that
argument doesn't count.