Pavel Emelianov [xemul@openvz.org] wrote:
| When clone() is invoked with CLONE_NEWPID, create a new pid namespace
| and then create a new struct pid for the new process. Allocate pid_t's
| for the new process in the new pid namespace and all ancestor pid
| namespaces. Make the newly cloned process the session and process group
| leader.
| 
| Since the active pid namespace is special and expected to be the first

active pid ns is the *last entry* in this patchset (not first) right ?

| entry in pid->upid_list, preserve the order of pid namespaces.
| 
| The size of 'struct pid' is dependent on the the number of pid namespaces
| the process exists in, so we use multiple pid-caches'. Only one pid cache
| is created during system startup and this used by processes that exist
| only in init_pid_ns.
| 
| When a process clones its pid namespace, we create additional pid caches
| as necessary and use the pid cache to allocate 'struct pids' for that depth.
| 
| Note, that with this patch the newly created namespace won't work, since
| the rest of the kernel still uses global pids, but this is to be fixed
| soon. Init pid namespace still works.
| 
| Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
| Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
| 
| ---
| 
|  include/linux/sched.h |    1 
|  kernel/fork.c         |   48 +++++++++++++++++---------
|  kernel/nsproxy.c      |    3 +
|  kernel/pid.c          |   91 +++++++++++++++++++++++++++++++++++++++++++++-----
|  4 files changed, 118 insertions(+), 25 deletions(-)
| 
| --- ./include/linux/sched.h.ve14	2007-08-06 15:00:09.000000000 +0400
| +++ ./include/linux/sched.h	2007-08-06 15:00:09.000000000 +0400
| @@ -27,6 +27,7 @@
|  #define CLONE_NEWUTS		0x04000000	/* New utsname group? */
|  #define CLONE_NEWIPC		0x08000000	/* New ipcs */
|  #define CLONE_NEWUSER		0x10000000	/* New user namespace */
| +#define CLONE_NEWPID		0x20000000	/* New pids */

Nit. I think "New pid namespace" would be a better comment.

Suka