On 04/22/2013 03:47 PM, Stefan Hajnoczi wrote:
On Thu, Apr 18, 2013 at 03:31:55PM +0400, Sergey Fedorov wrote:
Network hub should always receive incoming packets. Then forward them to
the appropriate port queue and let the qemu_send_packet() do the right
things. If the destination queue cannot receive the packet it will be
appended to the queue. When the receiver call
qemu_flush_queued_packets() later the queue will be really flushed and
no packets will be stalled in the sender network queue.
Signed-off-by: Sergey Fedorov <address@hidden>
---
net/hub.c | 20 --------------------
1 file changed, 20 deletions(-)
What is the point of this change? There is no semantic difference for
well-behaved net clients.
Does it fix a bug, if so, please include details?
Stefan
Yes, this fixes a bug. There were packet stalls when using user-mode
networking with USB network device. slirp_output() calls
qemu_send_packet() which eventually calls qemu_net_queue_send().
qemu_net_queue_send() calls qemu_can_send_packet(), which calls
can_receive() callback of network hub. Then
net_hub_port_can_receive() also calls qemu_can_send_packet() for
each port except packet source port.
Sometimes USB network device is not able to receive packet and
qemu_can_send_packet() returns false. In my case there is no more
ports and net_hub_port_can_receive() returns false. So
qemu_net_queue_send() call qemu_net_queue_append() instead of
qemu_net_queue_deliver(). qemu_net_queue_append() appends the packet
to the receiving port of the network hub which is not flushed when
USB netork device calls qemu_flush_queued_packets(). It is flushed
only when slirp resend the packet by timeout.
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(). And if the destination port
network client cannot receive the packet it will be queued in the
*destination* port network client queue. Queued packets from that
queue will be delivered as soon as the network client call
qemu_flush_queued_packets().