Am 10.01.2013 17:48, schrieb Stefan Hajnoczi:
> O_DIRECT on Linux has alignment requirements on I/O buffers and
> misaligned requests result in -EINVAL. The Linux virtio_blk guest
> driver usually submits aligned requests so I forgot to handle misaligned
> requests.
>
> It turns out that virtio-win guest drivers submit misaligned requests.
> Handle them using a bounce buffer that meets alignment requirements.
>
> Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> ---
> hw/dataplane/virtio-blk.c | 36 ++++++++++++++++++++++++++++++++++++
> 1 file changed, 36 insertions(+)
>
> diff --git a/hw/dataplane/virtio-blk.c b/hw/dataplane/virtio-blk.c
> index a6696b8..991ab5f 100644
> --- a/hw/dataplane/virtio-blk.c
> +++ b/hw/dataplane/virtio-blk.c
> @@ -34,6 +34,8 @@ typedef struct {
> struct iocb iocb; /* Linux AIO control block */
> QEMUIOVector *inhdr; /* iovecs for virtio_blk_inhdr */
> unsigned int head; /* vring descriptor index */
> + void *bounce_buffer; /* used if guest buffers are unaligned */
> + QEMUIOVector *read_qiov; /* for read completion /w bounce buffer
> */
> } VirtIOBlockRequest;
>
> struct VirtIOBlockDataPlane {
> @@ -89,6 +91,15 @@ static void complete_request(struct iocb *iocb, ssize_t
> ret, void *opaque)
>
> trace_virtio_blk_data_plane_complete_request(s, req->head, ret);
>
> + if (req->read_qiov) {
> + assert(req->bounce_buffer);
> + qemu_iovec_to_buf(req->read_qiov, 0, req->bounce_buffer, len);
Shouldn't it be qemu_iovec_from_buf()?
Makes me wonder if qtest cases might be doable...
> + qemu_iovec_destroy(req->read_qiov);
> + g_slice_free(QEMUIOVector, req->read_qiov);
> + }
> +
> + qemu_vfree(req->bounce_buffer);
> +
> qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
> qemu_iovec_destroy(req->inhdr);
> g_slice_free(QEMUIOVector, req->inhdr);
> @@ -136,6 +147,29 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool
> read,
> QEMUIOVector *inhdr)
> {
> struct iocb *iocb;
> + QEMUIOVector qiov;
> + struct iovec bounce_iov;
> + void *bounce_buffer = NULL;
> + QEMUIOVector *read_qiov = NULL;
> +
> + qemu_iovec_init_external(&qiov, iov, iov_cnt);
> + if (!bdrv_qiov_is_aligned(s->blk->conf.bs, &qiov)) {
> + /* Redirect I/O to aligned bounce buffer */
> + bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov.size);
> + bounce_iov.iov_base = bounce_buffer;
> + bounce_iov.iov_len = qiov.size;
> + iov = &bounce_iov;
> + iov_cnt = 1;
> +
> + if (read) {
> + /* Need to copy back from bounce buffer on completion */
> + read_qiov = g_slice_new(QEMUIOVector);
> + qemu_iovec_init(read_qiov, iov_cnt);
> + qemu_iovec_concat_iov(read_qiov, iov, iov_cnt, 0, qiov.size);
This would have to be the original iov and iov_cnt, but they are already
overwritten here.
> + } else {
> + qemu_iovec_to_buf(&qiov, 0, bounce_buffer, qiov.size);
> + }
> + }
>
> iocb = ioq_rdwr(&s->ioqueue, read, iov, iov_cnt, offset);
>
> @@ -143,6 +177,8 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
> VirtIOBlockRequest *req = container_of(iocb, VirtIOBlockRequest, iocb);
> req->head = head;
> req->inhdr = inhdr;
> + req->bounce_buffer = bounce_buffer;
> + req->read_qiov = read_qiov;
> return 0;
> }
Kevin
