On 2022/03/01 17:09, Vladislav Yaroshchuk wrote:
> Not sure that only one field is enough, cause > we may have two states on bh execution start: > 1. There are packets in vmnet buffer s->packets_buf > that were rejected by qemu_send_async and waiting > to be sent. If this happens, we should complete sending > these waiting packets with qemu_send_async firstly, > and after that we should call vmnet_read to get > new ones and send them to QEMU; > 2. There are no packets in s->packets_buf to be sent to > qemu, we only need to get new packets from vmnet > with vmnet_read and send them to QEMUIn case 1, you should just keep calling qemu_send_packet_async. Actually qemu_send_packet_async adds the packet to its internal queue and calls the callback when it is consumed. I'm not sure we can keep calling qemu_send_packet_async, because as docs from net/queue.c says: /* [...] * If a sent callback is provided to send(), the caller must handle a * zero return from the delivery handler by not sending any more packets * until we have invoked the callback. Only in that case will we queue * the packet. * * If a sent callback isn't provided, we just drop the packet to avoid * unbounded queueing. */ So after we did vmnet_read and read N packets into temporary s->packets_buf, we begin calling qemu_send_packet_async. If it returns 0 - it says "no more packets until sent_cb called please". At this moment we have N packets in s->packets_buf and already queued K < N of them. But, packets K..N are not queued and keep waiting for sent_cb to be sent with qemu_send_packet_async. Thus when sent_cb called, we should finish our transfer of packets K..N from s->packets_buf to qemu calling qemu_send_packet_async. I meant this.
I missed the comment. The description is contradicting with the actual code; qemu_net_queue_send_iov appends the packet to the queue whenever it cannot send one immediately.
Jason Wang, I saw you are in the MAINTAINERS for net/. Can you tell if calling qemu_send_packet_async is allowed after it returns 0?
Regards, Akihiko Odaki
