linux-kernel - Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd

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Date:	Fri, 13 Mar 2015 15:20:52 -0700
From:	josh@...htriplett.org
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Oleg Nesterov <oleg@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Thiago Macieira <thiago.macieira@...el.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
 exit notification via fd

On Fri, Mar 13, 2015 at 02:34:58PM -0700, Andy Lutomirski wrote:
> On Fri, Mar 13, 2015 at 12:57 PM,  <josh@...htriplett.org> wrote:
> > A process launching a new process with CLONE_FD is explicitly requesting
> > that the process be automatically reaped without any other process
> > having to wait on it.  The task needs to not become a zombie, because
> > otherwise, it'll show up in waitpid(-1, ...) calls in the parent
> > process, which would break the ability to use this to completely
> > encapsulate process management within a library and not interfere with
> > the parent's process handling via SIGCHLD and wait{pid,3,4}.
> 
> Wouldn't the correct behavior be to keep it alive as a zombie but
> *not* show it in waitpid, etc?

That's a significant change to the semantics of waitpid.  And then
someone would still need to wait on the process, which we'd like to
avoid.  (We don't want to have magic "reap on read(2)" semantics,
because among other things, what if we add a means in the future to get
an additional file descriptor corresponding to an existing process?)

- Josh Triplett
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