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

[Kirill Korotaev <dev@sw.ru>]

>>>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.
- clone has limited number of flags.
- sooner or later you will need to add flags about what and how you want 
to close (e.g. pspace with weak or strong isolation and so on)

> 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.
the problem is that in real life environments where executables can be 
substitutes this is kind of a security issue. Also I really hate the 
idea of using exec() for changing something.
In OpenVZ we successfully do context changes without exec()'s.

> 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?
Again, you concentrate on PIDspaces forgeting about all the other 
namespaces.

I would prefer:

- sys_ns_create()
creates namespace and makes a task to inherit this namespace. If 
_needed_, it _can_ fork inside.

- sys_ns_inherit()
change active namespace.

But how should we reference namespace? by globabl ID?

Kirill