From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262096AbUBXAAR (ORCPT ); Mon, 23 Feb 2004 19:00:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262100AbUBXAAR (ORCPT ); Mon, 23 Feb 2004 19:00:17 -0500 Received: from fw.osdl.org ([65.172.181.6]:57305 "EHLO mail.osdl.org") by vger.kernel.org with ESMTP id S262096AbUBXAAL (ORCPT ); Mon, 23 Feb 2004 19:00:11 -0500 Date: Mon, 23 Feb 2004 16:01:48 -0800 From: Andrew Morton To: Graham Swallow Cc: linux-kernel@vger.kernel.org Subject: Re: /proc/kmsg blocks with O_NONBLOCK, read() should return 0 with EAGAIN Message-Id: <20040223160148.400895f3.akpm@osdl.org> In-Reply-To: <20040223122410.6eb44df1.Information-Cascade@ntlworld.com> References: <20040223122410.6eb44df1.Information-Cascade@ntlworld.com> X-Mailer: Sylpheed version 0.9.7 (GTK+ 1.2.10; i586-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Graham Swallow wrote: > > /proc/kmsg blocks with O_NONBLOCK, read() should return 0 with EAGAIN > > fd = open( "/proc/kmsg", O_RDONLY|O_NONBLOCK ); > ... > poll() -- says read it > > len = read(fd,buff,len); // first read is fine > ... > len = read(fd,buff,len); // second read blocks > > I call read() a second time, because I'm feeling lucky, > (this is library code, which also reads from sockets). > > I expected it to return 0 with errno==EAGAIN. > Instead it waits: do_syslog(2,buf,count); > Does this work? diff -puN fs/proc/kmsg.c~kmsg-nonblock fs/proc/kmsg.c --- 24/fs/proc/kmsg.c~kmsg-nonblock Mon Feb 23 16:00:48 2004 +++ 24-akpm/fs/proc/kmsg.c Mon Feb 23 16:01:12 2004 @@ -32,6 +32,8 @@ static int kmsg_release(struct inode * i static ssize_t kmsg_read(struct file * file, char * buf, size_t count, loff_t *ppos) { + if ((file->f_flags & O_NONBLOCK) && !do_syslog(9, 0, 0)) + return -EAGAIN; return do_syslog(2,buf,count); } _