Re: [RF[CRAP] 2/2] xfs: stop using set_blocksize

[Christoph Hellwig <hch@infradead.org>]

On Mon, Apr 14, 2025 at 05:33:08PM -0700, Darrick J. Wong wrote:
> +/*
> + * For bdev filesystems that do not use buffer heads, check that this block
> + * size is acceptable and flush dirty pagecache to disk.
> + */

Can you turn this into a full fledged kerneldoc comment?

> +int bdev_use_blocksize(struct file *file, int size)
> +{
> +	struct inode *inode = file->f_mapping->host;
> +	struct block_device *bdev = I_BDEV(inode);
> +
> +	if (blk_validate_block_size(size))
> +		return -EINVAL;
> +
> +	/* Size cannot be smaller than the size supported by the device */
> +	if (size < bdev_logical_block_size(bdev))
> +		return -EINVAL;
> +
> +	if (!file->private_data)
> +		return -EINVAL;

This private_data check looks really confusing.  Looking it up I see
that it is directly copied from set_blocksize, but it could really
use a comment.  Or in fact be removed here and kept in set_blocksize
only as we don't care about an exclusive opener at all.   Even there
a comment would be rather helpful, though.

> +
> +	return sync_blockdev(bdev);
> +}

I don't think we need sync_blockdev here as we don't touch the
bdev page cache.  Maybe XFS wants to still call it, but it feels
wrong in a helper just validating the block size.

So maybe drop it, rename the helper to bdev_validate_block_size
and use it in set_blocksize instead of duplicating the logic?

> +	error = bdev_use_blocksize(btp->bt_bdev_file, sectorsize);

.. and then split using it in XFS into a separate patch from adding
the block layer helper.