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Message-ID: <20190124084011.GJ32526@8bytes.org>
Date: Thu, 24 Jan 2019 09:40:11 +0100
From: Joerg Roedel <joro@...tes.org>
To: Christoph Hellwig <hch@....de>
Cc: "Michael S . Tsirkin" <mst@...hat.com>,
Jason Wang <jasowang@...hat.com>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Jens Axboe <axboe@...nel.dk>,
virtualization@...ts.linux-foundation.org,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
iommu@...ts.linux-foundation.org, jfehlig@...e.com,
jon.grimm@....com, brijesh.singh@....com, jroedel@...e.de
Subject: Re: [PATCH 5/5] virtio-blk: Consider virtio_max_dma_size() for
maximum segment size
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
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