linux-ext4 - Re: [PATCH] common/rc: Fix _check_s

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Date:   Thu, 3 Dec 2020 09:15:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     ira.weiny@...el.com
Cc:     fstests@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Eric Sandeen <sandeen@...hat.com>,
        linux-kernel@...r.kernel.org,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        Jeff Moyer <jmoyer@...hat.com>, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH] common/rc: Fix _check_s_dax()

On Wed, Dec 02, 2020 at 01:41:45PM -0800, ira.weiny@...el.com wrote:
> From: Ira Weiny <ira.weiny@...el.com>
> 
> There is a conflict with the user visible statx bits 'mount root' and
> 'dax'.  The kernel is changing the dax bit to correct this conflict.[1]
> 
> Adjust _check_s_dax() to use the new bit.  Because DAX tests do not run
> on root mounts, STATX_ATTR_MOUNT_ROOT should always be 0, therefore we
> can allow either bit to indicate DAX and cover any kernel which may be
> running.
> 
> [1] https://lore.kernel.org/lkml/3e28d2c7-fbe5-298a-13ba-dcd8fd504666@redhat.com/
> 
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> ---
> 
> I went ahead and used Christoph's suggestion regarding using both bits.

That wasn't my suggestion.  I think we should always error out when
the bit value shared with STATX_ATTR_MOUNT_ROOT is seen.  Because that
means the kernel is not using or fixed ABI we agreed to use going
forward.