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Date:   Tue, 3 Oct 2023 08:23:26 +0100
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Subject: Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx
To:     "Darrick J. Wong" <djwong@kernel.org>,
        Dave Chinner <david@fromorbit.com>
Cc:     Bart Van Assche <bvanassche@acm.org>,
        Eric Biggers <ebiggers@kernel.org>, axboe@kernel.dk,
        kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
        jejb@linux.ibm.com, martin.petersen@oracle.com,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        chandan.babu@oracle.com, dchinner@redhat.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
        linux-api@vger.kernel.org,
        Prasad Singamsetty <prasad.singamsetty@oracle.com>
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From:   John Garry <john.g.garry@oracle.com>
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On 03/10/2023 03:57, Darrick J. Wong wrote:
>>>>> +#define STATX_ATTR_WRITE_ATOMIC        0x00400000 /* File
>>>>> supports atomic write operations */
>>>> How would this differ from stx_atomic_write_unit_min != 0?
>> Yeah, I suppose that we can just not set this for the case of
>> stx_atomic_write_unit_min == 0.
> Please use the STATX_ATTR_WRITE_ATOMIC flag to indicate that the
> filesystem, file and underlying device support atomic writes when
> the values are non-zero. The whole point of the attribute mask is
> that the caller can check the mask for supported functionality
> without having to read every field in the statx structure to
> determine if the functionality it wants is present.

Sure, but again that would be just checking atomic_write_unit_min_bytes 
or another atomic write block setting as that is the only way to tell 
from the block layer (if atomic writes are supported), so it will be 
something like:

if (request_mask & STATX_WRITE_ATOMIC && 
queue_atomic_write_unit_min_bytes(bdev->bd_queue)) {
     stat->atomic_write_unit_min =
       queue_atomic_write_unit_min_bytes(bdev->bd_queue);
     stat->atomic_write_unit_max =
       queue_atomic_write_unit_max_bytes(bdev->bd_queue);
     stat->attributes |= STATX_ATTR_WRITE_ATOMIC;
     stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;
     stat->result_mask |= STATX_WRITE_ATOMIC;
}

Thanks,
John