Il 22/04/2013 17:27, Fedorov Sergey ha scritto:
E.g. network hub has 3 ports. Suppose when iterating through port list
in net_hub_port_can_receive() a packet is successfully delivered to the
first port, and then is queued in the source port queue because the
second port cannot receive packets. Later net_hub_flush() will flush the
packet from the source port queue and it will be delivered in every
port. But it had been already delivered to one of them. So it will be
delivered twice to some ports. Moreover there is less chance to dequeue
the packet if several clients can't receive periodically.
Perhaps it is indeed wrong to do this blocking in can_receive()...
You're right that a hubport can always receive, but the hub itself
should have a queue. If one port cannot receive, the packet should be
appended to the hub's queue. And net_hub_flush will just go through the
hub's queue.
Anyway, actually there is no need in net_hub_port_can_receive() as the
network hub can always receive packets and pass it to its port network
clients with qemu_send_packet(). I think it's more natural solution.
I think the point was to keep dumps in sync with what actually happened
on the other ports. Otherwise a "-net dump" port will show the packet
immediately, even though it hasn't been delivered yet.
Paolo