Re: [v11][PATCH 9/9] Document clone_with_pids() syscall

From: "Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
To: Oren Laadan <orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org>
Cc: arnd-r2nGTMty4D4@public.gmane.org,
	Containers
	<containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	"Eric W. Biederman"
	<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>,
	hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org,
	Sukadev Bhattiprolu
	<sukadev-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	Alexey Dobriyan
	<adobriyan-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	roland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	Pavel Emelyanov <xemul-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org>
Subject: Re: [v11][PATCH 9/9] Document clone_with_pids() syscall
Date: Sun, 8 Nov 2009 09:09:35 -0600	[thread overview]
Message-ID: <20091108150935.GA14991__27744.6491098546$1257693058$gmane$org@us.ibm.com> (raw)
In-Reply-To: <4AF5ECFD.3000509-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org>

Quoting Oren Laadan (orenl-RdfvBDnrOixBDgjK7y7TUQ@public.gmane.org):
> Sukadev Bhattiprolu wrote:
> > Matt Helsley [matthltc-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org] wrote:
> > | > If userspace passes an array with n pids and there are k namespace levels
> > | > then clone_with_pids() makes sure that the kernel sees a pid array like:
> > | > 
> > | > index	  0     ... k - (n + 1)        ...          k - 1
> > | > 	+-----------------------+-------------------------+
> > | > pid_t	| 0 ..................0 | <copied from userspace> |
> > | > 	+-----------------------+-------------------------+
> > | 
> > | (diagram assumes n != k. If n == k then pids[0] is the pid desired
> > | in the initial namespace..)
> > 
> > True.
> > 
> > Also I was not sure if we should prevent choosing pids in ancestor containers.
> > since a process is not even supposed to know of ancestor namespaces. Is there
> > a need for choosing pids in those namespaces.

Yes, that is necessary.

> > | I don't know if it makes more sense to change clone_with_pids() or have
> > | [e]glibc wrappers swap the array contents.
> 
> I prefer to decide now on an order and stick to it in the kernel and
> in glibc.

Agreed!

I'd forgotten that, as Matt said, we can just specify pids to the depth
that we want, so I guess the current order is fine.

-serge