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SubjectRe: [PATCH 4/6] fs: xfs: Support atomic write for statx
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On 02/02/2024 18:05, Darrick J. Wong wrote:
> On Wed, Jan 24, 2024 at 02:26:43PM +0000, John Garry wrote:
>> Support providing info on atomic write unit min and max for an inode.
>>
>> For simplicity, currently we limit the min at the FS block size, but a
>> lower limit could be supported in future.
>>
>> The atomic write unit min and max is limited by the guaranteed extent
>> alignment for the inode.
>>
>> Signed-off-by: John Garry <john.g.garry@oracle.com>
>> ---
>> fs/xfs/xfs_iops.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>> fs/xfs/xfs_iops.h | 4 ++++
>> 2 files changed, 49 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
>> index a0d77f5f512e..0890d2f70f4d 100644
>> --- a/fs/xfs/xfs_iops.c
>> +++ b/fs/xfs/xfs_iops.c
>> @@ -546,6 +546,44 @@ xfs_stat_blksize(
>> return PAGE_SIZE;
>> }
>>
>> +void xfs_get_atomic_write_attr(
>
> static void?

We use this in the iomap and statx code

>
>> + struct xfs_inode *ip,
>> + unsigned int *unit_min,
>> + unsigned int *unit_max)
>
> Weird indenting here.

hmmm... I thought that this was the XFS style

Can you show how it should look?

>
>> +{
>> + xfs_extlen_t extsz = xfs_get_extsz(ip);
>> + struct xfs_buftarg *target = xfs_inode_buftarg(ip);
>> + struct block_device *bdev = target->bt_bdev;
>> + unsigned int awu_min, awu_max, align;
>> + struct request_queue *q = bdev->bd_queue;
>> + struct xfs_mount *mp = ip->i_mount;
>> +
>> + /*
>> + * Convert to multiples of the BLOCKSIZE (as we support a minimum
>> + * atomic write unit of BLOCKSIZE).
>> + */
>> + awu_min = queue_atomic_write_unit_min_bytes(q);
>> + awu_max = queue_atomic_write_unit_max_bytes(q);
>> +
>> + awu_min &= ~mp->m_blockmask;
>
> Why do you round /down/ the awu_min value here?

This is just to ensure that we returning *unit_min >= BLOCKSIZE

For example, if awu_min, max 1K, 64K from the bdev, we now have 0 and
64K. And below this gives us awu_min, max of 4k, 64k.

Maybe there is a more logical way of doing this.

>
>> + awu_max &= ~mp->m_blockmask;
>
> Actually -- since the atomic write units have to be powers of 2, why is
> rounding needed here at all?

Sure, but the bdev can report a awu_min < BLOCKSIZE

>
>> +
>> + align = XFS_FSB_TO_B(mp, extsz);
>> +
>> + if (!awu_max || !xfs_inode_atomicwrites(ip) || !align ||
>> + !is_power_of_2(align)) {
>
> ...and if you take my suggestion to make a common helper to validate the
> atomic write unit parameters, this can collapse into:
>
> alloc_unit_bytes = xfs_inode_alloc_unitsize(ip);
> if (!xfs_inode_has_atomicwrites(ip) ||
> !bdev_validate_atomic_write(bdev, alloc_unit_bytes)) > /* not supported, return zeroes */
> *unit_min = 0;
> *unit_max = 0;
> return;
> }
>
> *unit_min = max(alloc_unit_bytes, awu_min);
> *unit_max = min(alloc_unit_bytes, awu_max);

Again, we need to ensure that *unit_min >= BLOCKSIZE

Thanks,
John


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