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Re: [Qemu-discuss] [BUG or NOT] NICs in up state can not receive any pac

From: Rongqing Li
Subject: Re: [Qemu-discuss] [BUG or NOT] NICs in up state can not receive any packages if other one NIC is in down state
Date: Mon, 20 Aug 2012 14:26:33 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1

On 2012年08月17日 16:06, Stefan Hajnoczi wrote:
On Fri, Aug 17, 2012 at 09:38:45AM +0800, Rongqing Li wrote:

On 2012年08月16日 20:57, Stefan Hajnoczi wrote:
I think the solution is not to drop Vincent/Zhi Yong's code.  Instead we
should distinguish between "up" and "down".  If a net client is "up" but
cannot receive, then the hub will queue the packet.  If a net client is
"down" then the hub will ignore the client and send packets to other

I don't have patches for this but have added it to my TODO list.


Ok, Thanks for you explanation! and expect your patch.

If you have time to fix this I suggest you try to submit the patch
because I may not get to within the next week.

We need a way to determine whether the interface is up/down.  There is
already a link_down flag that can be set.  Not sure if its semantics are
exactly what we need, you'd need to check net.h/net.c.

The second step is looking at qemu_can_send_packet() and .can_receive().
net/hub.c:net_hub_port_can_receive() needs to be tweaked so peers with
link_down are skipped.


Hi Stefan:

Seem the link_down flags can not report if NIC is in down or in
up status.

Down the NIC by "ifconfig eth0 down", but link_down still is 0,
and "mii-tool eth0" says link is ready.

To e1000 dev, only "s->mac_reg[RCTL] & E1000_RCTL_EN" is 0 after
down it.

I did not find other flags and methods which reflect the NIC
up/down status.


Best Reagrds,
Roy | RongQing Li

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