[RFC][PATCH 7/7][v2] Define clone_with_pids syscall

[Sukadev Bhattiprolu]

Serge E. Hallyn [serue at us.ibm.com] wrote:
| Quoting Oren Laadan (orenl at cs.columbia.edu):
| > In general, can a task figure out it's depth in the pid-ns hierarchy ?
| 
| In user-space?  No.

Not from any existing user interface. But hypothetically or in the
long-term can/should sys_checkpoint() not be able to figure out if
it has to C/R say a bash shell that has nested pid namespaces ?

I am guessing sys_checkpoint() can know if its crossing a pid-ns
boundary by comparing or computing the max nesting level while
walking a process tree. i.e if task_pid(task)->pid_ns->level is
not the same for all process in the tree, then we have nested
namespaces. How to checkpoint/restart such a tree is of course a
bigger challenge.

But if sys_checkpoint() can find the max nesting level ? If that
info is saved in checkpoint image, clone_with_pids() could
use that info - no ?

| 
| That's why the task has to be allowed to specify only 2 pids, and
| have that mean 'auto-select all other pids'.
| 
| -serge