Date: Fri, 17 Mar 2006 15:04:31 -0500
From: Daniel Jacobowitz <dan@debian.org>
To: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>,
       linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] Proposed manpage additions for ptrace(2)
Message-ID: <20060317200431.GA20273@nevyn.them.org>
Mail-Followup-To: Chuck Ebbert <76306.1226@compuserve.com>,
	Michael Kerrisk <mtk-manpages@gmx.net>,
	linux-kernel <linux-kernel@vger.kernel.org>
References: <200603170647_MC3-1-BAD9-ED70@compuserve.com>
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On Fri, Mar 17, 2006 at 06:44:21AM -0500, Chuck Ebbert wrote:
> > Specifically, the three kinds of cloning are distinguished as:
> > 
> > if CLONE_VFORK -> PTRACE_EVENT_VFORK
> > else if clone exit signal == SIGCHLD -> PTRACE_EVENT_FORK
> > else PTRACE_EVENT_CLONE
> > 
> > You need to do some juggling to get the actual clone flags.
> 
> It might be best to leave these descriptions in terms of C library functions
> rather than kernel-internal.  Looking at sys_clone() and sys_fork() I can see
> what you mean but I'm not sure how to describe it to a programmer.

Those are user accessible flags.  Fork will give you a
PTRACE_EVENT_FORK, vfork will give you a PTRACE_EVENT_VFORK, but
clone may give you any of the above, depending on what arguments you
pass to it.  The SIGCHLD test matches the bit described in clone(2)
for __WALL or __WCLONE, for instance.

> > BTW, I believe there are still some potential deadlocks between
> > the vfork event and the vfork done event; I used to regularly generate
> > unkillable processes working on this code.
> 
> I have a test program and didn't hit any problems yet.  Maybe this was fixed?

One thing that IIRC was a problem was killing the parent before the
child (or maybe the other way round) when stopped at this point - such
as would happen if you typed "kill" at a GDB prompt after catch vfork.

-- 
Daniel Jacobowitz
CodeSourcery
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