From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754835AbbATMyH (ORCPT ); Tue, 20 Jan 2015 07:54:07 -0500 Received: from mail-wi0-f181.google.com ([209.85.212.181]:44008 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752499AbbATMyF (ORCPT ); Tue, 20 Jan 2015 07:54:05 -0500 Message-ID: <54BE4FE8.7030604@gmail.com> Date: Tue, 20 Jan 2015 13:54:00 +0100 From: "Michael Kerrisk (man-pages)" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Daniel Mack , Florian Weimer , David Herrmann , Greg Kroah-Hartman CC: mtk.manpages@gmail.com, Arnd Bergmann , "Eric W. Biederman" , One Thousand Gnomes , Tom Gundersen , Jiri Kosina , Andy Lutomirski , Linux API , linux-kernel , Djalal Harouni Subject: Re: kdbus: add documentation References: <1416546149-24799-1-git-send-email-gregkh@linuxfoundation.org> <1416546149-24799-2-git-send-email-gregkh@linuxfoundation.org> <871tolysbb.fsf@mid.deneb.enyo.de> <87vblwtxee.fsf@mid.deneb.enyo.de> <54BE0D56.5090301@gmail.com> <54BE1116.5060204@zonque.org> In-Reply-To: <54BE1116.5060204@zonque.org> 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 On 01/20/2015 09:25 AM, Daniel Mack wrote: > Hi Michael, > > On 01/20/2015 09:09 AM, Michael Kerrisk (man-pages) wrote: >> On 11/30/2014 06:23 PM, Florian Weimer wrote: >>> * David Herrmann: >>> >>>> On Sun, Nov 30, 2014 at 10:02 AM, Florian Weimer wrote: >>>>> * Greg Kroah-Hartman: >>>>> >>>>>> +7.4 Receiving messages >>> >>>>> What happens if this is not possible because the file descriptor limit >>>>> of the processes would be exceeded? EMFILE, and the message will not >>>>> be received? >>>> >>>> The message is returned without installing the FDs. This is signaled >>>> by EMFILE, but a valid pool offset. >>> >>> Oh. This is really surprising, so it needs documentation. But it's >>> probably better than the alternative (return EMFILE and leave the >>> message stuck, so that you receive it immediately again—this behavior >>> makes non-blocking accept rather difficult to use correctly). >> >> So, was this point in the end explicitly documented? I not >> obvious that it is documented in the revised kdbus.txt that >> Greg K-H sent out 4 days ago. > > No, we've revisited this point and changed the kernel behavior again in > v3. We're no longer returning -EMFILE in this case, but rather set > KDBUS_RECV_RETURN_INCOMPLETE_FDS in a new field in the receive ioctl > struct called 'return_flags'. We believe that's a nicer way of signaling > specific errors. The message will carry -1 for all FDs that failed to > get installed, so the user can actually see which one is missing. > > That's also documented in kdbus.txt, but we missed putting it into the > Changelog - sorry for that. Thanks for the info, Daniel. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/