netdev - Re: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect for sockets in accept(3)

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Date:	Fri, 23 Oct 2015 10:47:33 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alan Burlison <Alan.Burlison@...cle.com>
Cc:	Casper.Dik@...cle.com, Al Viro <viro@...IV.linux.org.uk>,
	David Miller <davem@...emloft.net>, stephen@...workplumber.org,
	netdev@...r.kernel.org, dholland-tech@...bsd.org
Subject: Re: [Bug 106241] New: shutdown(3)/close(3) behaviour is incorrect
 for sockets in accept(3)

On Fri, 2015-10-23 at 17:40 +0100, Alan Burlison wrote:
> On 23/10/2015 17:19, Eric Dumazet wrote:
> 
> >>> 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.



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