CLONE_PARENT in a container

[Sukadev Bhattiprolu]

Cc: Oleg, Eric

Oren Laadan [orenl at cs.columbia.edu] wrote:
| 
| What happens when a container-init calls clone() with the
| CLONE_PARENT flag set ?
| 
| Since CLONE_PARENT can be used to create a sibling, I'd
| think that this will create a sibling, in particular,  a
| new task in the same container whose parent is the parent
| of the container. From a quick look in the code I can't
| see why this would be impossible.
| 
| Is this so ?  Is this the desired behavior ?

Good question.  CLONE_PARENT was discussed recently on lkml but did
not look obvious to me who uses it or what the semantics are.
Some observations.

	- the "reaper" for this sibling would be the reaper of the
	  parent container, not the init of the new container.

	- if container-init exits, this sibling will also be killed since
	  it has a pid in this container.
	   
Not sure if it needs to be prevented though.  An using CLONE_PARENT
may want to run as a container-init :-) And if CLONE_PARENT is used
with CLONE_THREAD, we don't want to preclude threaded container-inits.

Sukadev