Re: [PATCH 03/21] fs/bdev: Add atomic write support info to statx

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On 03/10/2023 16:46, Darrick J. Wong wrote:
     stat->result_mask |= STATX_WRITE_ATOMIC;
The result_mask (which becomes the statx stx_mask) needs to have
STATX_WRITE_ATOMIC set any time a filesystem responds to
STATX_WRITE_ATOMIC being set in the request_mask, even if the response
is "not supported".

The attributes_mask also needs to have STATX_ATTR_WRITE_ATOMIC set if
the filesystem+file can support the flag, even if it's not currently set
for that file.  This should get turned into a generic vfs helper for the
next fs that wants to support atomic write units:

static void generic_fill_statx_atomic_writes(struct kstat *stat,
		struct block_device *bdev)
	u64 min_bytes;

	/* Confirm that the fs driver knows about this statx request */
	stat->result_mask |= STATX_WRITE_ATOMIC;

	/* Confirm that the file attribute is known to the fs. */
	stat->attributes_mask |= STATX_ATTR_WRITE_ATOMIC;

	/* Fill out the rest of the atomic write fields if supported */
	min_bytes = queue_atomic_write_unit_min_bytes(bdev->bd_queue);
	if (min_bytes == 0)

	stat->atomic_write_unit_min = min_bytes;
	stat->atomic_write_unit_max =

	/* Atomic writes actually supported on this file. */
	stat->attributes |= STATX_ATTR_WRITE_ATOMIC;

and then:

	if (request_mask & STATX_WRITE_ATOMIC)
		generic_fill_statx_atomic_writes(stat, bdev);

That looks sensible, but, if used by an FS, we would still need a method to include extra FS restrictions, like extent alignment as in 15/21.


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