From owner-freebsd-current@freebsd.org Mon Jul 18 23:11:53 2016 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 47D0AB9D854 for ; Mon, 18 Jul 2016 23:11:53 +0000 (UTC) (envelope-from alfred@freebsd.org) Received: from elvis.mu.org (elvis.mu.org [IPv6:2001:470:1f05:b76::196]) by mx1.freebsd.org (Postfix) with ESMTP id 39402187B for ; Mon, 18 Jul 2016 23:11:53 +0000 (UTC) (envelope-from alfred@freebsd.org) Received: from AlfredMacbookAir.local (unknown [IPv6:2601:645:8003:a4d6:c924:a77d:2190:5f76]) by elvis.mu.org (Postfix) with ESMTPSA id F143F346DFD1; Mon, 18 Jul 2016 16:11:52 -0700 (PDT) Subject: Re: difference in SIGCHLD behavior between Linux and FreeBSD breaks apt To: Matthew Macy , "freebsd-current@freebsd.org" References: <155c3a25e3f.11fb4143170445.2284890475527649192@nextbsd.org> From: Alfred Perlstein Organization: FreeBSD Message-ID: <884f17bd-7742-cc6f-0974-81c7bc833175@freebsd.org> Date: Mon, 18 Jul 2016 16:11:53 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 MIME-Version: 1.0 In-Reply-To: <155c3a25e3f.11fb4143170445.2284890475527649192@nextbsd.org> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 18 Jul 2016 23:11:53 -0000 I believe the On 7/6/16 9:34 PM, Matthew Macy wrote: > As a first step towards managing linux user space in a chrooted /compat/linux, initially for i915 testing with intel gpu tools, later on to get widevine and steam to work I'm trying to get apt to work. I've fixed a number of issues to date in pseudofs/linprocfs but now I'm running in to a bug caused by differences in SIGCHLD handling between Linux and FreeBSD. The situation is that apt will spawn dpkg and wait on a pipe read. On Linux when dpkg exits the SIGCHLD to apt causes a short read on the pipe which lets apt then continue. On FreeBSD a SIGCHLD is silently ignored. I've even experimented with doing a kill -20 to no effect. > > It would be easy enough to check sysvec against linux in pipe_read and break out of the loop when it's awakened from msleep (assuming there aren't deeper issues with signal propagation for anything other than SIGINT/SIGKILL) and then do a short read. However, I'm assuming that anyone who has worked in this area probably has a cleaner solution. > > Thanks in advance. Are you sure you need a hack in pipe_read and not one of the following possibilities: 1) a setting for the default signal disposition for linux processes needs to be fixed. 2) a flag set in p_flag2 that says set this behavior properly in a generic manner. Again not sure why you need to hack pipe_read and not just make sure that SIGCHLD is generated... Finally that sure is oddball behavior, dpkg probably has a bug where the parent is keeping the write side of the pipe open, you might be able to get them to take a patch upstream to fix that. -Alfred