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

[Joerg Roedel]

On Wed, Jan 23, 2019 at 10:31:39PM +0100, Christoph Hellwig wrote:
> 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.

In that case the limit would also apply to virtio-blk even if it doesn't
use the DMA-API. If that is acceptable we can move the check to
blk_queue_max_segment_size().

Regards,

	Joerg