On 7/18/16 4:15 PM, Matthew Macy wrote:

  ---- On Mon, 18 Jul 2016 16:11:53 -0700 Alfred Perlstein <alf...@freebsd.org> 
wrote ----
  > 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 <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.
  > >
  > > 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.

If you read my final mail it turns out I was holding a reference to the pipe in 
question in linprocfs. Maintaining the reference kept apt from getting the EOF 
on the pipe. I've since fixed this.


Ah that makes sense. :)

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