Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755629AbZGCAno (ORCPT ); Thu, 2 Jul 2009 20:43:44 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751917AbZGCAnh (ORCPT ); Thu, 2 Jul 2009 20:43:37 -0400 Received: from mail-vw0-f202.google.com ([209.85.212.202]:34214 "EHLO mail-vw0-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751847AbZGCAng convert rfc822-to-8bit (ORCPT ); Thu, 2 Jul 2009 20:43:36 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=XdM1hjnSHC7MgWY5VF5qKqmrgMDh0/Da9YuU2L0jjhjdFRWlDyJXYhkDKeae0vmuGp 2XH7hf5uLz+C7sTgpmN4tFMrILV/rhgnxTQG7BNWHighTiF0EtEP7DqB7yovpVnqz0eg uVE1kqK9YuQQWHx7c5W+JG+nCypYVmQ314j+I= MIME-Version: 1.0 In-Reply-To: <20090702102138.GF6372@cr0.nay.redhat.com> References: <412e6f7f0907020036y76abbc7du99c7b695f725be4@mail.gmail.com> <20090702091309.GB6372@cr0.nay.redhat.com> <412e6f7f0907020218m1f4a9651l2c682a9905925bcd@mail.gmail.com> <20090702094620.GE6372@cr0.nay.redhat.com> <412e6f7f0907020304u166b6d17id1bcf5d334b45c53@mail.gmail.com> <20090702102138.GF6372@cr0.nay.redhat.com> Date: Fri, 3 Jul 2009 08:43:39 +0800 Message-ID: <412e6f7f0907021743m6ed8ae10uecd13c4fc4ec7cbb@mail.gmail.com> Subject: Re: PROPOSAL: extend pipe() to support NULL argument. From: Changli Gao To: Amerigo Wang Cc: Linus Torvalds , Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2189 Lines: 73 On Thu, Jul 2, 2009 at 6:21 PM, Amerigo Wang wrote: > On Thu, Jul 02, 2009 at 06:04:02PM +0800, Changli Gao wrote: >>On Thu, Jul 2, 2009 at 5:46 PM, Amerigo Wang wrote: >>>>Are you familiar with splice() and tee()? They both use pipes as kernel buffers. >>> >>> You are not answering the question, obviously. >>When you use pipes as kernel buffer handlers, two fd isn't necessary. >>Using one will save half of fd resources. Is it obviously? > > Not really.. I can't see any reason why you use this method to save > fd's... pick read(2)/write(2). In order to use splice, you must have pipe first. The common code is: int fd[2]; pipe(fd); splice(infd, NULL, fd[1], NULL, getpagesize(), SPLICE_F_MOVE); splice(fd[0], NULL, outfd, NULL, getpagesize(), SPLICE_F_MOVE); close(fd[0]); close(fd[1]); if pipe supports NULL argument, and returnes a RW pipe fd in that case, the code will become: int fd; fd = pipe(NULL); splice(infd, NULL, fd, NULL, getpagesize(), SPLICE_F_MOVE); splice(fd, NULL, outfd, NULL, getpagesize(), SPLICE_F_MOVE); close(fd); One fd is saved. > >> >>> >>> And you snipped too much, how can you return that fd? Using the return value? >>one RW file descriptor is returned. I have answered this in the first post. > > No, you never say *how* it is returned. return value. save in %eax in i386. > >> >>> Ah! This will probably break the user-space program... >>> >>I don't think so. As a skillful programmer, who will trasfter pipe() a >>NULL pointer? In any way, it is break sth, but not very seriously, and >>won't affact any right and robust program. > > Huh? Isn't the code sample below too common? > > if (pipe(...)) >   perror("pipe"); > > Currently pipe(2) can make sure this is robust. > > You are trying to break it... > It depends on the argument for pipe, if the argument is NULL, it breaks the code above. -- Regards， Changli Gao(xiaosuo@gmail.com) -- 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/