Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755507AbZGCIPF (ORCPT ); Fri, 3 Jul 2009 04:15:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751935AbZGCIOq (ORCPT ); Fri, 3 Jul 2009 04:14:46 -0400 Received: from mail-px0-f190.google.com ([209.85.216.190]:49442 "EHLO mail-px0-f190.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753850AbZGCIOp (ORCPT ); Fri, 3 Jul 2009 04:14:45 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:content-transfer-encoding :in-reply-to:user-agent; b=Xn7BVClsuMPbAZzrTcnZErFAqjKx1Dvlqxc1Hhryfp+UE4qJ1HLT1YplUdeEHnKt6n b7s/pKVNuZAwAmaog3+Bdh2kRQ7xALNY3J1SIzn9Quvwza41WxYVvd5A36D0EeCRxTln tYtreOI2fHNNiyqyOXM2sLruQnrczSn+b7Iws= Date: Fri, 3 Jul 2009 16:16:55 +0800 From: Amerigo Wang To: Changli Gao Cc: Amerigo Wang , Linus Torvalds , Linux Kernel Mailing List Subject: Re: PROPOSAL: extend pipe() to support NULL argument. Message-ID: <20090703081655.GH5880@cr0.nay.redhat.com> References: <20090702102138.GF6372@cr0.nay.redhat.com> <412e6f7f0907021743m6ed8ae10uecd13c4fc4ec7cbb@mail.gmail.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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <412e6f7f0907030040v6133badat7058186a01d78f44@mail.gmail.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1456 Lines: 44 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)... 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. > >> >> 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. -- 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/