Re: [PATCH] Introduce ActivePid: in /proc/self/status (v2, was Vpid:)

[Greg Kurz <gkurz@fr.ibm.com>]

On Thu, 2011-06-16 at 08:07 -0700, Eric W. Biederman wrote:
> > Finally, we thought that the 'ActivePid' information was interesting 
> > enough to be exposed in /proc and was solving the case we're facing 
> > rather easily with some framework (cgroups) in user space.
> 
> The pid number by which a process knows itself doesn't seem
> unreasonable.  I'm not totally 
> 
> After having a second look at the code in proc we already have
> a reference to the struct pid we want to print.  So simply
> printing
> pid->numbers[pid->level].nr
> seems reasonable, and race free.
> 
> Alternatively that could be written.
> pid_nr_ns(pid, ns_of_pid(pid));
> 
> Eric

So we end up with the following, since pid is valid:

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 5e4f776..b7316cc 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -183,12 +183,14 @@ static inline void task_state(struct seq_file *m,
struct pid_namespace *ns,
 		"Pid:\t%d\n"
 		"PPid:\t%d\n"
 		"TracerPid:\t%d\n"
+		"ActivePid:\t%d\n"
 		"Uid:\t%d\t%d\t%d\t%d\n"
 		"Gid:\t%d\t%d\t%d\t%d\n",
 		get_task_state(p),
 		task_tgid_nr_ns(p, ns),
 		pid_nr_ns(pid, ns),
 		ppid, tpid,
+		pid_nr_ns(pid, ns_of_pid(pid)),
 		cred->uid, cred->euid, cred->suid, cred->fsuid,
 		cred->gid, cred->egid, cred->sgid, cred->fsgid);

-- 
Gregory Kurz                                     gkurz@fr.ibm.com
Software Engineer @ IBM/Meiosys                  http://www.ibm.com
Tel +33 (0)534 638 479                           Fax +33 (0)561 400 420

"Anarchy is about taking complete responsibility for yourself."
        Alan Moore.