On Fri, 2015-10-23 at 17:40 +0100, Alan Burlison wrote:

On 23/10/2015 17:19, Eric Dumazet wrote:

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The AF_UNIX poll one? No, I don't have the means to do so, and in any
case that's not a POSIX issue, just a plain bug. I'm happy to log a bug
if that helps.

BTW, there is no kernel bug here. POSIX poll() man page says :

POLLOUT
     Normal data may be written without blocking.

If you attempt to write on a listener, write() does _not_ block and
returns -1, which seems correct behavior to me, in accordance with man
page.

Except of course data may not be written, because an attempt to actually 
do so fails, because the socket is in the listen state, is not connected 
and therefore no attempt to write to it could ever succeed. The only bit 
of the required behaviour that the current AF_UNIX poll implementation 
actually gets right is the "without blocking" bit, and that's only the 
case because the failure is detected immediately and the write call 
returns immediately with an error.

Yeah, I know some people use poll(NULL, 0, timeout) to implement
msleep().

Because it definitely impresses friends.

So why not poll(&pfd, 1, timeout) to do the same, with a socket listener
and POLLOUT in pfd.events

Go figure. I'll send the fine patch.

Thanks.