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SubjectRe: [PATCH 4/6] fs: xfs: Support atomic write for statx
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On 13/02/2024 17:37, Darrick J. Wong wrote:
>> 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?
> The parameter declarations should line up with the local variables:
>
> void
> xfs_get_atomic_write_attr(
> struct xfs_inode *ip,
> unsigned int *unit_min,
> unsigned int *unit_max)
> {
> struct xfs_buftarg *target = xfs_inode_buftarg(ip);
> struct block_device *bdev = target->bt_bdev;
> struct request_queue *q = bdev->bd_queue;
> struct xfs_mount *mp = ip->i_mount;
> unsigned int awu_min, awu_max, align;
> xfs_extlen_t extsz = xfs_get_extsz(ip);
>
>>>> +{
>>>> + 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_min = roundup(queue_atomic_write_unit_min_bytes(q),
> mp->m_sb.sb_blocksize);
>
> ?

Yeah, I think that all this can be simplified to be made more obvious.

>
>>>> + 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
> The file allocation unit and hence the return value of
> xfs_inode_alloc_unitsize is always a multiple of sb_blocksize.

Right, but this value is coming from HW and we are just ensuring that
the awu_min which we report is >= BLOCKSIZE. xfs_inode_alloc_unitsize()
return value will really guide unit_max.

Anyway, again I can make this all more obvious.

Thanks,
John



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