Re: [PATCH 05/26] loop: regularize upgrading the lock size for direct I/O

[Damien Le Moal <dlemoal@kernel.org>]

On 6/11/24 2:19 PM, Christoph Hellwig wrote:
> The LOOP_CONFIGURE path automatically upgrades the block size to that
> of the underlying file for O_DIRECT file descriptors, but the
> LOOP_SET_BLOCK_SIZE path does not.  Fix this by lifting the code to
> pick the block size into common code.

s/lock/block in the commit title.

> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/block/loop.c | 25 +++++++++++++++----------
>  1 file changed, 15 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index c658282454af1b..4f6d8514d19bd6 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -975,10 +975,24 @@ loop_set_status_from_info(struct loop_device *lo,
>  	return 0;
>  }
>  
> +static unsigned short loop_default_blocksize(struct loop_device *lo,
> +		struct block_device *backing_bdev)
> +{
> +	/* In case of direct I/O, match underlying block size */
> +	if ((lo->lo_backing_file->f_flags & O_DIRECT) && backing_bdev)
> +		return bdev_logical_block_size(backing_bdev);
> +	return 512;

Nit: SECTOR_SIZE ?

> +}
> +
>  static int loop_reconfigure_limits(struct loop_device *lo, unsigned short bsize)
>  {
> +	struct file *file = lo->lo_backing_file;
> +	struct inode *inode = file->f_mapping->host;
>  	struct queue_limits lim;
>  
> +	if (!bsize)
> +		bsize = loop_default_blocksize(lo, inode->i_sb->s_bdev);

If bsize is specified and there is a backing dev used with direct IO, should it
be checked that bsize is a multiple of bdev_logical_block_size(backing_bdev) ?

> +
>  	lim = queue_limits_start_update(lo->lo_queue);
>  	lim.logical_block_size = bsize;
>  	lim.physical_block_size = bsize;
> @@ -997,7 +1011,6 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
>  	int error;
>  	loff_t size;
>  	bool partscan;
> -	unsigned short bsize;
>  	bool is_loop;
>  
>  	if (!file)
> @@ -1076,15 +1089,7 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
>  	if (!(lo->lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
>  		blk_queue_write_cache(lo->lo_queue, true, false);
>  
> -	if (config->block_size)
> -		bsize = config->block_size;
> -	else if ((lo->lo_backing_file->f_flags & O_DIRECT) && inode->i_sb->s_bdev)
> -		/* In case of direct I/O, match underlying block size */
> -		bsize = bdev_logical_block_size(inode->i_sb->s_bdev);
> -	else
> -		bsize = 512;
> -
> -	error = loop_reconfigure_limits(lo, bsize);
> +	error = loop_reconfigure_limits(lo, config->block_size);
>  	if (WARN_ON_ONCE(error))
>  		goto out_unlock;
>  

-- 
Damien Le Moal
Western Digital Research