On Thu, 07/02 14:30, Stefan Hajnoczi wrote:
> On Tue, Jun 30, 2015 at 10:29:20AM +0800, Fam Zheng wrote:
> > It returns true as long as there is another attached port. This is not
> > strictly necessary because even if there is only one port (the sender),
> > net_hub_port_receive could succeed with a NOP. So always deliver the
> > packets, instead of queuing them.
> >
> > This fixes the possible hanging issue after net layer changed how
> > can_read is handled. That is, if net_hub_port_can_receive returned
> > false, the peer would disable the queue until it's explicitly flushed
> > (for example, a call to qemu_flush_queued_packets() in net_hub_add_port,
> > where net_hub_port_can_receive() would become true). This patch avoids
> > that complication.
> >
> > Signed-off-by: Fam Zheng <f...@redhat.com>
> > ---
> > net/hub.c | 20 --------------------
> > 1 file changed, 20 deletions(-)
>
> Hmm...I misread the hub code:
>
> net_hub_port_can_receive() returns true if *any* port can receive.
>
> net_hub_receive_iov() always accepts packets. It never discards or
> queues.
>
> So in order to move to the semantics you want, let's drop
> net_hub_port_can_receive() *and* change net_hub_receive_iov():
>
> static ssize_t net_hub_receive(NetHub *hub, NetHubPort *source_port,
> const uint8_t *buf, size_t len)
> {
> NetHubPort *port;
>
> QLIST_FOREACH(port, &hub->ports, next) {
> if (port == source_port) {
> continue;
> }
>
> /* No need for a callback because net_hub_flush() is called
> * when the peer flushes the queue anyway.
> *
> * Note that packets are duplicated if there are multiple
> * ports and some of them accepted a packet before a later
> * port queued it. Live with it, the network tolerates
> * duplicates.
> */
> if (qemu_send_packet(&port->nc, buf, len) == 0) {
> return 0;
I'm not sure if it is a good idea to return 0 from either net_hub_port_receive
or net_hub_receive. Because that way if one out of ten ports is down, other
ones will no longer get more packets from tap.
Fam
> }
> }
> return len;
> }
