Date: Thu, 7 Jul 2016 09:28:40 +0300 From: Andrey Chernov <ache@freebsd.org> To: "K. Macy" <kmacy@freebsd.org>, Don Lewis <truckman@freebsd.org> Cc: "mmacy@nextbsd.org" <mmacy@nextbsd.org>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org>, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org> Subject: Re: difference in SIGCHLD behavior between Linux and FreeBSD breaks apt Message-ID: <558d9bff-0f9b-2b08-b057-32b2a41953ff@freebsd.org> In-Reply-To: <CAHM0Q_O3Apy86DZqDBXnJJ6axMhVPu0xHngoJoHQqKe1QN4%2BgA@mail.gmail.com> References: <155c3a25e3f.11fb4143170445.2284890475527649192@nextbsd.org> <201607070443.u674hsgK007808@gw.catspoiler.org> <CAHM0Q_O3Apy86DZqDBXnJJ6axMhVPu0xHngoJoHQqKe1QN4%2BgA@mail.gmail.com>
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On 07.07.2016 7:52, K. Macy wrote: > On Wednesday, July 6, 2016, Don Lewis <truckman@freebsd.org> 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 <apt pid> 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
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