From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff King Subject: Re: RLIMIT_NOFILE fallback Date: Wed, 18 Dec 2013 16:28:48 -0500 Message-ID: <20131218212847.GA13685@sigill.intra.peff.net> References: <20131218171446.GA19657@kitenet.net> <20131218191702.GA9083@sigill.intra.peff.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: Joey Hess , git@vger.kernel.org To: Junio C Hamano X-From: git-owner@vger.kernel.org Wed Dec 18 22:29:09 2013 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VtOfu-0002tt-9B for gcvg-git-2@plane.gmane.org; Wed, 18 Dec 2013 22:29:02 +0100 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754758Ab3LRV2y (ORCPT ); Wed, 18 Dec 2013 16:28:54 -0500 Received: from cloud.peff.net ([50.56.180.127]:46923 "HELO peff.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751942Ab3LRV2w (ORCPT ); Wed, 18 Dec 2013 16:28:52 -0500 Received: (qmail 8344 invoked by uid 102); 18 Dec 2013 21:28:52 -0000 Received: from va-71-48-137-223.dhcp.embarqhsd.net (HELO sigill.intra.peff.net) (71.48.137.223) (smtp-auth username relayok, mechanism cram-md5) by peff.net (qpsmtpd/0.84) with ESMTPA; Wed, 18 Dec 2013 15:28:52 -0600 Received: by sigill.intra.peff.net (sSMTP sendmail emulation); Wed, 18 Dec 2013 16:28:48 -0500 Content-Disposition: inline In-Reply-To: Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: On Wed, Dec 18, 2013 at 11:50:24AM -0800, Junio C Hamano wrote: > -------------------------------- 8< ------------------------------ > > static unsigned int get_max_fd_limit(void) > { > #ifdef RLIMIT_NOFILE > struct rlimit lim; > > if (!getrlimit(RLIMIT_NOFILE, &lim)) > return lim.rlim_cur; > #endif > > #if defined(_SC_OPEN_MAX) > { > long sc_open_max = sysconf(_SC_OPEN_MAX); > if (0 < sc_open_max) > return sc_open_max; > } > > #if defined(OPEN_MAX) > return OPEN_MAX; > #else > return 1; /* see the caller ;-) */ > #endif > } > > -------------------------------- >8 ------------------------------ Yeah, with the #endif followup you posted, this is what I had in mind. > But the sysconf part makes me wonder; here is what we see in > http://pubs.opengroup.org/onlinepubs/9699919799/functions/sysconf.html > > If name is an invalid value, sysconf() shall return -1 and set errno > to indicate the error. If the variable corresponding to name is > described in as a maximum or minimum value and the > variable has no limit, sysconf() shall return -1 without changing > the value of errno. Note that indefinite limits do not imply > infinite limits; see . > > For a broken system (like RLIMIT_NOFILE defined for the compiler, > but the actual call returns a bogus error), the compiler may see the > _SC_OPEN_MAX defined, while sysconf() may say "I've never heard of > such a name" and return -1, or the system, whether broken or not, > may want to say "Unlimited" and return -1. The caller takes > anything unreasonable as a positive value capped to 25 or something, > so there isn't a real harm if we returned a bogus value from here, > but I am not sure what the safe default behaviour of this function > should be to help such a broken system while not harming systems > that are functioning correctly. According to the POSIX quote above, it sounds like we could do: #if defined (_SC_OPEN_MAX) { long max; errno = 0; max = sysconf(_SC_OPEN_MAX); if (0 < max) /* got the limit */ return max; else if (!errno) /* unlimited, cast to int-max */ return max; /* otherwise, fall through */ } #endif Obviously you could collapse the two branches of the conditional, though I think it deserves at least a comment to explain what is going on. -Peff