On Sun, 2007-06-17 at 17:25 +0300, Avi Kivity wrote: > Rusty Russell wrote: > > + /* 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?
We could actually do this for write, but not for read (where the length & sector need to be sent to other end, and the data comes from other end). The strict separation of in and out in virtio is to support both untrusted inter-guest I/O (admittedly not useful for block devices) and socket-style hypercall interfaces. Thanks, Rusty. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
