Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751274AbWAIEz4 (ORCPT ); Sun, 8 Jan 2006 23:55:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751275AbWAIEzz (ORCPT ); Sun, 8 Jan 2006 23:55:55 -0500 Received: from x35.xmailserver.org ([69.30.125.51]:6325 "EHLO x35.xmailserver.org") by vger.kernel.org with ESMTP id S1751274AbWAIEzz (ORCPT ); Sun, 8 Jan 2006 23:55:55 -0500 X-AuthUser: davidel@xmailserver.org Date: Sun, 8 Jan 2006 20:55:44 -0800 (PST) From: Davide Libenzi X-X-Sender: davide@localhost.localdomain To: David Schwartz cc: Linux Kernel Mailing List Subject: RE: [PATCH/RFC] POLLHUP tinkering ... In-Reply-To: Message-ID: References: X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1724 Lines: 47 On Sun, 8 Jan 2006, David Schwartz wrote: > >> From: Davide Libenzi >> 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 there is an error, an error event must be returned. An edge-triggered > interface must report every event that occurs with an indication of that > type. Yes, that's the case. >> 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. > > If the connection closes and the edge-triggered interface does not give a > HUP indication, then it is broken. Same as above. I think DaveM was thinking at the classical poll/select usage scenario, where the wait queue head stays in the device's wait queue only during the poll/select system call. With epoll, they're resident and always collection events through wakeups (callbacks in the epoll case) done by the device on its poll wait queue. - Davide - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/