Re: [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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