[Bug 175269] truss(1): truss -ff doesn't detach from processes properly

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=175269

John Baldwin <jhb at FreeBSD.org> changed:

           What    |Removed                     |Added
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                 CC|                            |jhb at FreeBSD.org

--- Comment #2 from John Baldwin <jhb at FreeBSD.org> ---
So when I run this I get an error from kill saying that -<pid> doesn't exist. 
And in particular, sh doesn't create a new process group when it runs a script,
so there is no process group to kill so this keeps running forever.  When you
run rsleeper.sh directly from the shell it is run in a new process group by the
shell which is why your 'kill -$$' works.

I tried modifying truss to create a new process group for the child process,
but the result of this is that the tty driver in the kernel no longer sends a
SIGINT to anything when Ctrl-C is pressed.  (I ktrace'd the shell with
inheritance and no processes got a SIGINT when Ctrl-C was hit).  Note also that
the problem isn't that truss is stuck trying to detach, the problem is that the
child isn't exiting (and the Ctrl-C should be forcing the child to exit).  This
probably has something to do with truss being the parent that the shell
originally forks rather than being a "helper" process.  Hmm, so truss
explicitly ignores SIGINT/TERM/QUIT when exec'ing and the comment above that
says "they should be passed off to the process", but using SIG_IGN doesn't do
that.  Instead, it needs to "forward" signals to the child process.

So I did a patch to forward the signals, and then also placed the new process
in its own process group.  This fixed the rsleeper.sh case, but probably needs
a bit more testing.  Also, I'm not sure why you are using 'truss -ff' as the
double -f doesn't mean anything to truss.

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