Am 05.12.2012 21:47, schrieb Stefan Hajnoczi:
> virtio-blk-data-plane is a subset implementation of virtio-blk. It only
> handles read, write, and flush requests. It does this using a dedicated
> thread that executes an epoll(2)-based event loop and processes I/O
> using Linux AIO.
>
> This approach performs very well but can be used for raw image files
> only. The number of IOPS achieved has been reported to be several times
> higher than the existing virtio-blk implementation.
>
> Eventually it should be possible to unify virtio-blk-data-plane with the
> main body of QEMU code once the block layer and hardware emulation is
> able to run outside the global mutex.
>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> +static int process_request(IOQueue *ioq, struct iovec iov[],
> + unsigned int out_num, unsigned int in_num,
> + unsigned int head)
> +{
> + VirtIOBlockDataPlane *s = container_of(ioq, VirtIOBlockDataPlane,
> ioqueue);
> + struct iovec *in_iov = &iov[out_num];
> + struct virtio_blk_outhdr outhdr;
> + QEMUIOVector *inhdr;
> + size_t in_size;
> +
> + /* Copy in outhdr */
> + if (unlikely(iov_to_buf(iov, out_num, 0, &outhdr,
> + sizeof(outhdr)) != sizeof(outhdr))) {
> + error_report("virtio-blk request outhdr too short");
> + return -EFAULT;
> + }
> + iov_discard(&iov, &out_num, sizeof(outhdr));
> +
> + /* Grab inhdr for later */
> + in_size = iov_size(in_iov, in_num);
> + if (in_size < sizeof(struct virtio_blk_inhdr)) {
> + error_report("virtio_blk request inhdr too short");
> + return -EFAULT;
> + }
> + inhdr = g_slice_new(QEMUIOVector);
> + qemu_iovec_init(inhdr, 1);
> + qemu_iovec_concat_iov(inhdr, in_iov, in_num,
> + in_size - sizeof(struct virtio_blk_inhdr),
> + sizeof(struct virtio_blk_inhdr));
> + iov_discard(&in_iov, &in_num, -sizeof(struct virtio_blk_inhdr));
> +
> + /* TODO Linux sets the barrier bit even when not advertised! */
> + outhdr.type &= ~VIRTIO_BLK_T_BARRIER;
> +
> + struct iocb *iocb;
> + switch (outhdr.type & (VIRTIO_BLK_T_OUT | VIRTIO_BLK_T_SCSI_CMD |
> + VIRTIO_BLK_T_FLUSH)) {
> + case VIRTIO_BLK_T_IN:
> + iocb = ioq_rdwr(ioq, true, in_iov, in_num, outhdr.sector * 512);
> + break;
> +
> + case VIRTIO_BLK_T_OUT:
> + iocb = ioq_rdwr(ioq, false, iov, out_num, outhdr.sector * 512);
> + break;
> +
> + case VIRTIO_BLK_T_SCSI_CMD:
> + /* TODO support SCSI commands */
> + fail_request_early(s, head, inhdr, VIRTIO_BLK_S_UNSUPP);
> + return 0;
> +
> + case VIRTIO_BLK_T_FLUSH:
> + /* TODO fdsync not supported by Linux AIO, do it synchronously here!
> */
> + fdatasync(s->fd);
We shouldn't ignore errors here.
> + fail_request_early(s, head, inhdr, VIRTIO_BLK_S_OK);
> + return 0;
> +
Kevin
