Re: difference in SIGCHLD behavior between Linux and FreeBSD breaks apt

On Wednesday, July 6, 2016, Don Lewis <truckman_at_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.

-M

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