cgroups: add a read-only "procs" file similar to "tasks" that shows only unique tgids
struct cgroup used to have a bunch of fields for keeping track of the
pidlist for the tasks file. Those are now separated into a new struct
cgroup_pidlist, of which two are had, one for procs and one for tasks.
The way the seq_file operations are set up is changed so that just the
pidlist struct gets passed around as the private data.
Interface example: Suppose a multithreaded process has pid 1000 and other
threads with ids 1001, 1002, 1003:
$ cat tasks
1000
1001
1002
1003
$ cat cgroup.procs
1000
$
Signed-off-by: Ben Blum <bblum@google.com>
Signed-off-by: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c833d6f..2357733 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -141,6 +141,17 @@
CGRP_WAIT_ON_RMDIR,
};
+struct cgroup_pidlist {
+ /* protects the other fields */
+ struct rw_semaphore mutex;
+ /* array of xids */
+ pid_t *list;
+ /* how many elements the above list has */
+ int length;
+ /* how many files are using the current array */
+ int use_count;
+};
+
struct cgroup {
unsigned long flags; /* "unsigned long" so bitops work */
@@ -179,14 +190,9 @@
*/
struct list_head release_list;
- /* pids_mutex protects the fields below */
- struct rw_semaphore pids_mutex;
- /* Array of process ids in the cgroup */
- pid_t *tasks_pids;
- /* How many files are using the current tasks_pids array */
- int pids_use_count;
- /* Length of the current tasks_pids array */
- int pids_length;
+ /* we will have two separate pidlists, one for pids (the tasks file)
+ * and one for tgids (the procs file). */
+ struct cgroup_pidlist tasks, procs;
/* For RCU-protected deletion */
struct rcu_head rcu_head;