netdev - non-symmetric Unix dgram sockets and poll

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Date:	Wed, 2 Feb 2011 17:36:40 +0000
From:	Alban Crequy <alban.crequy@...labora.co.uk>
To:	netdev@...r.kernel.org
Subject: non-symmetric Unix dgram sockets and poll

Hi,

I have 3 Unix dgram sockets (sockA, sockB, sockC):
- sockA is connected to sockB.
- sockB is connected to sockC.
- sockC is not connected.

SockA cannot send any message to sockB because net/unix/af_unix.c::unix_may_send()
prevents it. Is there any reason for that restriction?

If it was possible to send that message, unix_dgram_poll() on sockB could be in a
situation where it needs to add the current process in 2 different wait queues:
- sk_sleep(sk) for POLLIN (messages coming from sockA)
- &unix_sk(other)->peer_wait for POLLOUT (to send messages to sockC)

Is it correct?

Thanks,
Alban
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