Re: [PATCH 5/5] virtio-blk: Consider virtio_max_dma_size() for maximum segment size

[Christoph Hellwig]

On Wed, Jan 23, 2019 at 05:30:49PM +0100, Joerg Roedel wrote:
> +	max_size = virtio_max_dma_size(vdev);
> +
>  	/* Host can optionally specify maximum segment size and number of
>  	 * segments. */
>  	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
>  				   struct virtio_blk_config, size_max, &v);
>  	if (!err)
> -		blk_queue_max_segment_size(q, v);
> -	else
> -		blk_queue_max_segment_size(q, -1U);
> +		max_size = min(max_size, v);
> +
> +	blk_queue_max_segment_size(q, max_size);

I wonder if we should just move the dma max segment size check
into blk_queue_max_segment_size so that all block drivers benefit
from it.  Even if not I think at least the SCSI midlayer should
be updated to support it.

Btw, I wonder why virtio-scsi sticks to the default segment size,
unlike virtio-blk.