From owner-freebsd-current@freebsd.org Thu Jul 7 06:28:50 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 7CA18B76D6C for ; Thu, 7 Jul 2016 06:28:50 +0000 (UTC) (envelope-from mailing-machine@vniz.net) Received: from mail-lf0-f46.google.com (mail-lf0-f46.google.com [209.85.215.46]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 0B5761ECD for ; Thu, 7 Jul 2016 06:28:49 +0000 (UTC) (envelope-from mailing-machine@vniz.net) Received: by mail-lf0-f46.google.com with SMTP id l188so4878934lfe.2 for ; Wed, 06 Jul 2016 23:28:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=EdmFlZ1aF8fhmSd8eppdAdvgKXWYd1kULvgaG+xbvvg=; b=RZnIuZNQ5vusyYNM8wTHm2vc8fMXnzaB8qGHgq+dOEJSQ9Epbksx7qD33mU8Eesxum 3tmv7mzKsDMiBma7UMQ8Vc/I82mvvd367YQs35iD0w/2z8OEI3GcqjtgNkhGZ+UfHXOx S3Gmli7whMm97fBHkrVQcKEwAQV4dZ2DiI0ycumxvuWmj56bmSfKveQKGV9PwjevZMgI ViF9qG850PamVo0TBUYLVmDLWpCjYAbLTAW/57EXmOOe6CoTSqkR6Iif68H0N4wx0fIX MQkjGueZ1VRelkza74CBG1vgmamlLe3MNKywMAgChNSNl294zYGFCSmonjBEeDaX2CAH e1gQ== X-Gm-Message-State: ALyK8tJ3kmzHtKrV8Y2LU1bYPjklybeTrGZ7JWZJDL2B5DbdpZwseAz4M3zmLj3DuSMFDw== X-Received: by 10.25.21.16 with SMTP id l16mr5460245lfi.99.1467872922271; Wed, 06 Jul 2016 23:28:42 -0700 (PDT) Received: from [192.168.1.2] ([89.169.173.68]) by smtp.gmail.com with ESMTPSA id a199sm705946lfe.35.2016.07.06.23.28.41 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jul 2016 23:28:41 -0700 (PDT) Subject: Re: difference in SIGCHLD behavior between Linux and FreeBSD breaks apt To: "K. Macy" , Don Lewis References: <155c3a25e3f.11fb4143170445.2284890475527649192@nextbsd.org> <201607070443.u674hsgK007808@gw.catspoiler.org> Cc: "mmacy@nextbsd.org" , "freebsd-current@freebsd.org" , "freebsd-hackers@freebsd.org" From: Andrey Chernov Message-ID: <558d9bff-0f9b-2b08-b057-32b2a41953ff@freebsd.org> Date: Thu, 7 Jul 2016 09:28:40 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=us-ascii 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: Thu, 07 Jul 2016 06:28:50 -0000 On 07.07.2016 7:52, K. Macy wrote: > On Wednesday, July 6, 2016, Don Lewis wrote: > >> On 6 Jul, 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. >> >> It shoulds like SA_RESTART is set in sa_flags for SIGCHLD but shouldn't >> be in this case. > > > > Good point. > > Thinking more about it, this seems like a bug in FreeBSD. Not a valid > behavioral difference. You better need consult with POSIX before fixing things toward any Linuxisms blindly in our native code. I don't have a time now to see, is it really a bug according to POSIX, but please read or just find all SIGCHLD there: http://pubs.opengroup.org/onlinepubs/9699919799/functions/wait.html it explain SIGCHLD actions in deep details. And that one too: http://pubs.opengroup.org/onlinepubs/009695399/functions/sigaction.html