Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754644AbZGCI1n (ORCPT ); Fri, 3 Jul 2009 04:27:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752095AbZGCI13 (ORCPT ); Fri, 3 Jul 2009 04:27:29 -0400 Received: from qw-out-2122.google.com ([74.125.92.27]:63099 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751742AbZGCI11 convert rfc822-to-8bit (ORCPT ); Fri, 3 Jul 2009 04:27:27 -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=HUqAcSg8FE1pIbntjxzmXTGl/HgpfYtwkQj98VethF0FDW42qfh2iTrASHRlyeGGwe AIlFAH3rqc+93RDafoRj05x9OG7goCEoFgn9KM+QKk7RJ+kJp34yRfC5+Jct8gAWiR/C 31Nab4uvaKXyzLKiJi1qcOPnzXWlF1l1uLzUg= MIME-Version: 1.0 In-Reply-To: <20090703081655.GH5880@cr0.nay.redhat.com> References: <20090702102138.GF6372@cr0.nay.redhat.com> <20090703015554.GB5880@cr0.nay.redhat.com> <412e6f7f0907021910w64af0525h17afb518f0e18f97@mail.gmail.com> <20090703030008.GD5880@cr0.nay.redhat.com> <412e6f7f0907022108p7c533ed2wd16fceb0f282ed62@mail.gmail.com> <20090703051917.GE5880@cr0.nay.redhat.com> <412e6f7f0907022242r52ad981fyd51c2a55f41ab228@mail.gmail.com> <20090703071504.GG5880@cr0.nay.redhat.com> <412e6f7f0907030040v6133badat7058186a01d78f44@mail.gmail.com> <20090703081655.GH5880@cr0.nay.redhat.com> Date: Fri, 3 Jul 2009 16:27:29 +0800 Message-ID: <412e6f7f0907030127u3d6806dfo9168600e7c71b241@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: 2056 Lines: 60 On Fri, Jul 3, 2009 at 4:16 PM, Amerigo Wang wrote: > On Fri, Jul 03, 2009 at 03:40:34PM +0800, Changli Gao wrote: >>On Fri, Jul 3, 2009 at 3:15 PM, Amerigo Wang wrote: >>> >>> If saving one fd really helps here, probably you want to >>> save more, you will need a syscall like: >>> >>>  int splice_without_new_fd(int infd, int outfd); >>Do you know sendfile()? Its current implementation is buggy, and will >>be blocked on outfd. Anyway, the above code is just a use case, there >>are other cases sendfile can't cover. > > So what? So you should fix it intead of inventing a new pipe() and use > splice(2)... I said: It just a special case. Fixing sendfile() won't fix everything. > > Wait... if splice(2) doesn't block, what is your point for saving > an fd in your code? You can do: > > int splice_two_fd(int fd1, int fd2) > { >        int fds[2]; >        pipe(fds); >        splice(fd1, fds[0]);//not block >        splice(fds[1], fd2);//not block >        close(fds[0]); //can be closed soon >        close(fds[1]); //ditto > } > > Outside this function no new fd's are used. > In fact, sendfile(2) is implemented via splice(2) infrastructure. The logic is the same, and much clever than yours. Dive into its code, you will find the reason why it must be blocked on outfd. >> >>> >>> But splice(2) is designed to be as it is. You need to increase >>> your fd limit, instead of saving one by pipe(). >>> >>I don't agree with you. We should save resource as much as we can, and >>not work around it. > > You are saying splice(2) is wrong? Because it is splice(2) who > needs 3 fd's finally. > It isn't splice(2)'s fault. In fact, I can also work around this issue by named pipe. -- 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/