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From: Scott Feldman <sfeldma@gmail.com>
Date: Tue, 30 Jun 2015 00:49:12 -0400
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To: QEMU Developers <qemu-devel@nongnu.org>, famz@redhat.com, Stefan Hajnoczi <stefanha@redhat.com>
Cc: =?UTF-8?B?SmnFmcOtIFDDrXJrbw==?= <jiri@resnulli.us>

Hi Fam, Stefan,

I'm running a test with rocker device using UDP sockets connections
and I'm seeing the socket s->read_poll stay disabled if the device
receives a packet when the device's can_receive returns false.
Receive is stuck after that; nothing ever re-enables s->read_poll.  I
see the first packet queued on queue->packets and that's it.   No more
receives.  If I modify the device to lie and always return
can_receive=true, and drop the pkt in driver receive, then things work
fine.

I think this patch broke can_receive semantics for net/socket.c:

commit 6e99c631f116221d169ea53953d91b8aa74d297a
Author: Fam Zheng <famz@redhat.com>
Date:   Thu Jun 4 14:45:16 2015 +0800

    net/socket: Drop net_socket_can_send

Anything jump out?

(In the test, rocker device is enabling the netdev port once the guest
OS driver signals to enable the port based on STP process running on
the guest.  The initial STP state is DISABLED, so the port is isolated
from the network.  As STP algo progresses, the port is opened up and
the netdev is enabled for Rx traffic).

-scott