From owner-freebsd-bugs@FreeBSD.ORG Sat Apr 14 13:20:12 2012 Return-Path: Delivered-To: freebsd-bugs@hub.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 86E89106564A for ; Sat, 14 Apr 2012 13:20:12 +0000 (UTC) (envelope-from gnats@FreeBSD.org) Received: from freefall.freebsd.org (freefall.freebsd.org [IPv6:2001:4f8:fff6::28]) by mx1.freebsd.org (Postfix) with ESMTP id 579B18FC08 for ; Sat, 14 Apr 2012 13:20:12 +0000 (UTC) Received: from freefall.freebsd.org (localhost [127.0.0.1]) by freefall.freebsd.org (8.14.5/8.14.5) with ESMTP id q3EDKCjN076998 for ; Sat, 14 Apr 2012 13:20:12 GMT (envelope-from gnats@freefall.freebsd.org) Received: (from gnats@localhost) by freefall.freebsd.org (8.14.5/8.14.5/Submit) id q3EDKCSE076995; Sat, 14 Apr 2012 13:20:12 GMT (envelope-from gnats) Date: Sat, 14 Apr 2012 13:20:12 GMT Message-Id: <201204141320.q3EDKCSE076995@freefall.freebsd.org> To: freebsd-bugs@FreeBSD.org From: Jeremie Le Hen Cc: Subject: Re: bin/166660: [libc] [patch] New util/shlib to change per-fd default stdio buffering mode X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Jeremie Le Hen List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 14 Apr 2012 13:20:12 -0000 The following reply was made to PR bin/166660; it has been noted by GNATS. From: Jeremie Le Hen To: John Baldwin Cc: Jeremie Le Hen , bug-followup@freebsd.org Subject: Re: bin/166660: [libc] [patch] New util/shlib to change per-fd default stdio buffering mode Date: Sat, 14 Apr 2012 15:11:31 +0200 On Tue, Apr 10, 2012 at 09:43:16AM -0400, John Baldwin wrote: > On Monday, April 09, 2012 5:21:03 pm Jeremie Le Hen wrote: > > Hi John, > > > > On Mon, Apr 09, 2012 at 11:30:08AM -0400, John Baldwin wrote: > > > I think it would be fine to do this in libc directly rather than via > > > LD_PRELOAD. That would let it work for static binaries as well as > > > dynamic libraries. My understanding is that this is how stdbuf works on > > > Linux (glibc honors the relevant magic environment variables). To that > > > end, I think it would be ok to move this into libc directly. > > > > I thought it would be too expensive to check for three (actually up to > > six, see below) in such a critical path. Moreover, this would have > > lowered a lot my chances to see this committed simply because very few > > committers would have taken the responsibility for this and the time to > > handle the debates that would have sprouted. > > > > Your point for static binaries is very valid but aren't you afraid of > > the performance impact? I'll try to spare some time this week to move > > libstdbuf code into libc and do some benchmarks. > > Hmm, I hadn't considered the performance impact, but to be honest, this > is stdio. :) If it only happens once when stdio is first used then I think > this is fine to do in libc. I looked in the stdio source to see how I could implement there efficiently, but the problem is that there isn't a single entry point. The best I can do I think is basically something like this: int stdbuf_done = 0; void _stdbuf() { /* libstdbuf code */ stdbuf_done = 1; } #define STDBUF() if (!stdbuf_done) _stdbuf() And scatter STDBUF() all around. What do you think of it? (FWIW, I checked how Linux implemented this, they used an additional shared library.) > > > One more question, do you use the same environment variable as glibc for > > > this, or do you use a different scheme? > > > > I didn't like the GNU variable names (_STDBUF_I, _STDBUF_O and > > _STDBUF_E) so I used STDBUF_0, STDBUF_1 and STDBUF_2 instead. But the > > former are supported for obvious compatibility reasons. To be honest I > > don't really care about the names, we can use the GNU ones if you think > > it's better to avoid doing to much strcmp(3), especially if we but the > > code in the libc startup path. > > If the variable values have the same semantics, then I think it is best to > simply use the same names as glibc. Ok, I'll do this. -- Jeremie Le Hen Men are born free and equal. Later on, they're on their own. Jean Yanne