From: Colin Walters Subject: Re: [PATCH] nextfd(2) Date: Wed, 04 Apr 2012 13:10:12 -0400 Message-ID: <1333559412.10230.67.camel@lenny> References: <20120401125741.GA7484@p183.telecom.by> <4F7A3CC2.1040200@zytor.com> <4F7C777E.10608@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "H. Peter Anvin" , Alexey Dobriyan , akpm@linux-foundation.org, viro@zeniv.linux.org.uk, torvalds@linux-foundation.org, drepper@gmail.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org To: KOSAKI Motohiro Return-path: In-Reply-To: <4F7C777E.10608@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2012-04-04 at 09:31 -0700, KOSAKI Motohiro wrote: > Ideally possible. but practically impossible. 2) people don't use a their > own malloc. they only uses open sources alternative malloc. And, I think > you have too narrowing concern. Even though malloc people adds a workaround, > the standard inhibit to use it What do you mean? If as hpa says, the maintainer of e.g. google tcmalloc added a call to pthread_atfork(), then code which uses opendir() would start working. > and people may continue to use more dangerous > RLIM_NOFILE loop. 1) I haven't seen _practical_ userland software uses such > linux internal hacking. Almost all major software can run on multiple OSs. Except that if you're using /proc/self/fd, you're already relying on Linux-specific functionality. So it's not burdensome to use "struct linux_dirent" and O_DIRECTORY either. In GLib we're presently doing the regular /proc+opendir() under #ifdef __linux__: http://git.gnome.org/browse/glib/tree/glib/gspawn.c#n932 Now I'd happily switch to hpa's fdwalk() implementation if I was aware of someone using glib in combination with an alternative malloc hitting this problem. Basically I think hpa is right here, and it's not really worth adding a new system call. The thing is, even if it were added today, since we need to run on old kernels, we'd have to carry the code to use the /proc trick approximately forever. And in the end all nextfd() would accomplish would be a *third* case in the already messy ifdefs/fallbacks in the various implementations of process spawning.