Hi Stefan, Thanks for your reply.
On Thu, Aug 15, 2019 at 7:07 AM Stefan Hajnoczi <stefa...@gmail.com> wrote: > > On Wed, Aug 14, 2019 at 10:54:34AM -0700, William Tu wrote: > > Hi, > > > > I'm using libvhost-user.a to write a vhost backend, in order to receive and > > send packets from/to VMs from OVS. I started by reading the > > vhost-user-bridge.c. > > I can now pass the initialization stage, seeing .queue_set_started get > > invoked. > > > > However, I am stuck at receiving the packet from VM. > > So is it correct to do: > > 1) check vu_queue_empty, started, and aval_bytes, if OK, then > > This step can be skipped because vu_queue_pop() returns NULL if there > are no virtqueue elements available. > > > 2) elem = vu_queue_pop(&dev->vudev, vq, sizeof(VuVirtqElement)); > > 3) the packet payload should be at elem->in_sg->iov_base + hdrlen? or > > at elem->out_sg? > > The driver->device buffers are elem->out_sg and the device->driver > buffers are elem->in_sg. OK, thanks. Then for vswitch to receive from qemu, I should check device->driver. > > Device implementations must not make assumptions about the layout of > out_sg and in_sg (e.g. you cannot assume that in_sg[0]->iov_len == > sizeof(struct virtio_net_hdr) and you must handle the case where > in_sg[0]->iov_len == 1). OK so I might need to copy to a single continuous buffer. > > > I tried to hex dump the iov_base, but the content doesn't look like > > having a ethernet header. I saw in vubr_backend_recv_cb at > > vhost-user-bridge.c, > > we're creating another iovec and recvmsg(vubr->backend_udp_sock, &msg, 0); > > I don't think I have to create backend UDP sock, am I correct? > > Please see the VIRTIO specification for details of the virtio-net rx/tx > virtqueue formats: > https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-2050006 > > I think you may need to handle the struct virtio_net_hdr that comes > before the Ethernet header. Thank, will look at it. William > > Stefan
