The current implementation may change the packet layout when vnet_hdr needs an endianness swap. The layout change causes one more iov to be added to the iov[] passed from the guest, which is a barrier to making the TX queue size 1024 due to the possible off-by-one issue.
This patch changes the implementation to remain the packet layout intact. In this case, the number of iov[] passed to writev will be equal to the number obtained from the guest. Signed-off-by: Wei Wang <wei.w.w...@intel.com> --- hw/net/virtio-net.c | 29 ++++++++++++++--------------- 1 file changed, 14 insertions(+), 15 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index 7d091c9..a51e9a8 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -1287,8 +1287,7 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) for (;;) { ssize_t ret; unsigned int out_num; - struct iovec sg[VIRTQUEUE_MAX_SIZE], sg2[VIRTQUEUE_MAX_SIZE + 1], *out_sg; - struct virtio_net_hdr_mrg_rxbuf mhdr; + struct iovec sg[VIRTQUEUE_MAX_SIZE], mhdr, *out_sg; elem = virtqueue_pop(q->tx_vq, sizeof(VirtQueueElement)); if (!elem) { @@ -1305,7 +1304,10 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) } if (n->has_vnet_hdr) { - if (iov_to_buf(out_sg, out_num, 0, &mhdr, n->guest_hdr_len) < + /* Buffer to copy vnet_hdr and the possible adjacent data */ + mhdr.iov_len = out_sg[0].iov_len; + mhdr.iov_base = g_malloc0(mhdr.iov_len); + if (iov_to_buf(out_sg, out_num, 0, mhdr.iov_base, mhdr.iov_len) < n->guest_hdr_len) { virtio_error(vdev, "virtio-net header incorrect"); virtqueue_detach_element(q->tx_vq, elem, 0); @@ -1313,17 +1315,12 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) return -EINVAL; } if (n->needs_vnet_hdr_swap) { - virtio_net_hdr_swap(vdev, (void *) &mhdr); - sg2[0].iov_base = &mhdr; - sg2[0].iov_len = n->guest_hdr_len; - out_num = iov_copy(&sg2[1], ARRAY_SIZE(sg2) - 1, - out_sg, out_num, - n->guest_hdr_len, -1); - if (out_num == VIRTQUEUE_MAX_SIZE) { - goto drop; - } - out_num += 1; - out_sg = sg2; + virtio_net_hdr_swap(vdev, mhdr.iov_base); + /* Copy the first iov where the vnet_hdr resides in */ + out_num = iov_copy(sg, 1, &mhdr, 1, 0, mhdr.iov_len); + out_num += iov_copy(sg + 1, ARRAY_SIZE(sg) - 1, out_sg + 1, + elem->out_num - 1, 0, -1); + out_sg = sg; } } /* @@ -1345,13 +1342,15 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) ret = qemu_sendv_packet_async(qemu_get_subqueue(n->nic, queue_index), out_sg, out_num, virtio_net_tx_complete); + if (n->has_vnet_hdr) { + g_free(mhdr.iov_base); + } if (ret == 0) { virtio_queue_set_notification(q->tx_vq, 0); q->async_tx.elem = elem; return -EBUSY; } -drop: virtqueue_push(q->tx_vq, elem, 0); virtio_notify(vdev, q->tx_vq); g_free(elem); -- 2.7.4