Date: Sun, 8 Jan 2006 16:11:10 -0800 (PST)
From: Davide Libenzi <davidel@xmailserver.org>
To: "David S. Miller" <davem@davemloft.net>
cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH/RFC] POLLHUP tinkering ...
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On Sun, 8 Jan 2006, David S. Miller wrote:

> From: Davide Libenzi <davidel@xmailserver.org>
> Date: Sun, 8 Jan 2006 16:02:10 -0800 (PST)
>
>> But if and hangup happened with some data (data + FIN), they won't
>> receive any more events for the Linux poll subsystem (and epoll,
>> when using the event triggered interface), so they are forced to
>> issue an extra read() after the loop to detect the EOF
>> condition. Besides from the extra read() overhead, the code does not
>> come exactly pretty.
>
> The extra last read is always necessary, it's an error synchronization
> barrier.  Did you know that?
>
> If a partial read or write hits an error, the successful amount of
> bytes read or written before the error occurred is returned.  Then any
> subsequent read or write will report the error immediately.

Sorry for the missing info, but I was clearly talking about O_NONBLOCK 
here.


- Davide


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