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To:     Christoph Hellwig <hch@lst.de>, ira.weiny@intel.com
Cc:     fstests@vger.kernel.org, Eric Sandeen <sandeen@redhat.com>,
        linux-kernel@vger.kernel.org,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Chinner <david@fromorbit.com>,
        "Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
        Jeff Moyer <jmoyer@redhat.com>, linux-ext4@vger.kernel.org,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        David Howells <dhowells@redhat.com>
References: <20201202214145.1563433-1-ira.weiny@intel.com>
 <20201203081556.GA15306@lst.de>
From:   Eric Sandeen <sandeen@sandeen.net>
Subject: Re: [PATCH] common/rc: Fix _check_s_dax()
Message-ID: <b757842d-b020-49c9-498c-df5de89f10af@sandeen.net>
Date:   Thu, 3 Dec 2020 11:55:50 -0600
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On 12/3/20 2:15 AM, Christoph Hellwig wrote:
> On Wed, Dec 02, 2020 at 01:41:45PM -0800, ira.weiny@intel.com wrote:
>> From: Ira Weiny <ira.weiny@intel.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@intel.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.

*nod* and my suggestion was to explicitly test for the old/wrong value and
offer the test-runner a hint about why it may have been set (missing the
fix commit), but we should still ultimately fail the test when it is seen.

-Eric