|
From: | Fedorov Sergey |
Subject: | Re: [Qemu-devel] [PATCH] net/hub: remove can_receive handler |
Date: | Mon, 22 Apr 2013 16:26:16 +0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 |
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().
-- Best regards, Sergey Fedorov, Junior Software Engineer, Samsung R&D Institute Rus. E-mail: address@hidden
[Prev in Thread] | Current Thread | [Next in Thread] |