Date: Wed, 06 Jul 2016 23:59:43 -0700 From: Matthew Macy <mmacy@nextbsd.org> To: "Andrey Chernov" <ache@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, "Don Lewis" <truckman@freebsd.org>, "freebsd-current@freebsd.org" <freebsd-current@freebsd.org>, "K. Macy" <kmacy@freebsd.org> Subject: Re: difference in SIGCHLD behavior between Linux and FreeBSD breaks apt Message-ID: <155c427b1ea.e316552376378.990303254341485453@nextbsd.org> In-Reply-To: <2249b671-765a-13e5-3b19-862416f6f73d@freebsd.org> References: <155c3a25e3f.11fb4143170445.2284890475527649192@nextbsd.org> <201607070443.u674hsgK007808@gw.catspoiler.org> <CAHM0Q_O3Apy86DZqDBXnJJ6axMhVPu0xHngoJoHQqKe1QN4%2BgA@mail.gmail.com> <558d9bff-0f9b-2b08-b057-32b2a41953ff@freebsd.org> <155c41681bb.1141d206175455.3130944807853755277@nextbsd.org> <2249b671-765a-13e5-3b19-862416f6f73d@freebsd.org>
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---- On Wed, 06 Jul 2016 23:48:53 -0700 Andrey Chernov <ache@freebsd.org> wrote ---- > On 07.07.2016 9:40, Matthew Macy wrote: > > > > > > > > ---- On Wed, 06 Jul 2016 23:28:40 -0700 Andrey Chernov <ache@freebsd.org> wrote ---- > > > 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 > > > > > > > > I was pretty clear in my initial email that I'm only interested in changing behavior for Linux programs. > > Of course, but in case it is FreeBSD bug, it should be fixed in our > native code first before making any changes in Linuxator. > > > And I was asking for help with that, not a link to SUSv3 or POSIX. > > In case I was not helpful, sorry for that. Before you try to change > something in Linuxator you need to be sure that FreeBSD does it right > (or wrong, then fix FreeBSD native code first). I am just insisting on > proper steps of fixing it. > I'm sorry for snapping . I misunderstood your intent. Using a SIGCHLD to deliberately interrupt a pipe read is such a weird idiom. I'll test fork vs clone on Linux and see how OS X responds to a SIGCHLD during a pipe read. Thanks. -M > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >
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