netdev - Re: [PATCH] net: netlink: don't try unicast when dst_pid is zero for NETLINK

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Message-ID: <BANLkTimXZ0gU0F0SpmUuUwEsnD3MGSnJcA@mail.gmail.com>
Date:	Sat, 14 May 2011 08:50:37 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] net: netlink: don't try unicast when dst_pid is zero for NETLINK_USERSOCK

On Sat, May 14, 2011 at 4:48 AM, David Miller <davem@...emloft.net> wrote:
> From: Changli Gao <xiaosuo@...il.com>
> Date: Fri, 13 May 2011 14:24:54 +0800
>
>> For NETLINK_USERSOCK, no one listens on PID 0, so sending a message only to
>> to a multicast group should not return -ECONNREFUSED.
>>
>> Signed-off-by: Changli Gao <xiaosuo@...il.com>
>
> I don't think this is a great idea, creating different semantics for
> NETLINK_USERSOCK vs. other types.
>
> You have to set the pid to something which will receive the unicast
> message, and then you can also (on top of that) send it to a multicast
> group as well.
>
> But the base operation is always the unicast send, and that is what
> determines success/failure of the operation.
>

Yes, I have seen that the return value of netlink_broadcast() isn't
returned to the caller, so the caller can't know whether the message
broadcasted is sent successfully or not. It isn't a big problem, as
netlink isn't a reliable datagram protocol. Without this patch
applied, we can also send a message to a multicast group only, but
ignore the -ECONNREFUSED error.

Thanks.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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