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xen-devel
[Xen-devel] Re: [PATCH RFC 3/3] Virtio draft III: example block driver
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To: |
Rusty Russell <rusty@xxxxxxxxxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH RFC 3/3] Virtio draft III: example block driver |
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From: |
Avi Kivity <avi@xxxxxxxxxxxx> |
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Date: |
Sun, 17 Jun 2007 17:25:21 +0300 |
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Cc: |
Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>, Xen Mailing List <xen-devel@xxxxxxxxxxxxxxxxxxx>, "jmk@xxxxxxxxxxxxxxxxxxx" <jmk@xxxxxxxxxxxxxxxxxxx>, kvm-devel <kvm-devel@xxxxxxxxxxxxxxxxxxxxx>, virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>, Christian Borntraeger <cborntra@xxxxxxxxxx>, Latchesar Ionkov <lionkov@xxxxxxxx>, Suzanne McIntosh <skranjac@xxxxxxxxxx>, Jens Axboe <jens.axboe@xxxxxxxxxx>, Martin Schwidefsky <schwidefsky@xxxxxxxxxx> |
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Sun, 17 Jun 2007 07:23:37 -0700 |
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Rusty Russell wrote:
+static bool do_read(request_queue_t *q, struct virtio_blk *vblk,
+ struct virtblk_req *vbr)
+{
+ unsigned long num;
+
+ vbr->out_hdr.type |= VIRTIO_BLK_T_READ;
+
+ /* Set up for reply. */
+ vblk->sg[0].page = virt_to_page(&vbr->in_hdr);
+ vblk->sg[0].offset = offset_in_page(&vbr->in_hdr);
+ vblk->sg[0].length = sizeof(vbr->in_hdr);
+ num = blk_rq_map_sg(q, vbr->req, vblk->sg+1);
+ vbr->out_hdr.id = vblk->vdev->ops->add_inbuf(vblk->vdev, vblk->sg,
+ 1+num, vbr);
+ if (IS_ERR_VALUE(vbr->out_hdr.id))
+ goto full;
+
+ vblk->sg[0].page = virt_to_page(&vbr->out_hdr);
+ vblk->sg[0].offset = offset_in_page(&vbr->out_hdr);
+ vblk->sg[0].length = sizeof(vbr->out_hdr);
+
+ vbr->out_id = vblk->vdev->ops->add_outbuf(vblk->vdev, vblk->sg, 1,
+ vbr);
This strikes me as wasteful. Why not set up a single descriptor which
contains both placement and the data itself?
--
error compiling committee.c: too many arguments to function
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