Re: [RFC][PATCH 04/20] pspace: Allow multiple instaces of the process id namespace

["Serge E. Hallyn" <serue@us.ibm.com>]

Quoting Herbert Poetzl (herbert@13thfloor.at):
> > I also don't understand why you are eager to introduce new sys calls 
> > like pkill(path_to_process), but is trying to use waitpid() for pspace 
> > die notifications? Maybe it is simply better to introduce container 
> > specific syscalls which should be clean and tidy, instead of messing 
> > things up with clone()/waitpid() and so on? The more simple code we 
> > have, the better it is for all of us.
> 
> now that you mention it, maybe we should have a few
> rounds how those 'generic' container syscalls would 
> look like?

I still like the following:

clone(): extended with flags for asking a private copy of various
	namespaces.  For the CLONE_NEWPIDSPACE flag, the pid which
	is returned to the parent process is it's handle to the
	new pidspace.

sys_execpid(pid, argv, envp): exec a new syscall with the requested
	pid, if the pid is available.  Else either return an error,
	or pick a random pid.  Error makes sense to me, but that's
	probably debatable.

sys_fork_slide(pid): fork and slide into the pidspace belong to pid.
	This way we can do things like

	p = sys_fork_slide(2794);
	if (p == 0) {
		kill(2974);
	} else {
		waitpid(p, 0, 0);
	}

Ok, this last one in particular needs to be improved, but these two
syscalls and the clone flags together give us all we need.  Right?

-serge
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