introduce the walk_process_tree() helper

Add the new helper to walk the process tree, the next patch adds a user.
Note that it visits the group leaders only, proc_visitor can do
for_each_thread itself or we can trivially extend walk_process_tree() to
do this.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d233422..6261bfc 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3053,6 +3053,9 @@ extern bool current_is_single_threaded(void);
 #define for_each_process_thread(p, t)  \
        for_each_process(p) for_each_thread(p, t)
 
+typedef int (*proc_visitor)(struct task_struct *p, void *data);
+void walk_process_tree(struct task_struct *top, proc_visitor, void *);
+
 static inline int get_nr_threads(struct task_struct *tsk)
 {
        return tsk->signal->nr_threads;

diff --git a/kernel/fork.c b/kernel/fork.c
index 11c5c8a..135b7a4 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2053,6 +2053,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 }
 #endif
 
+void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
+{
+       struct task_struct *leader, *parent, *child;
+       int res;
+
+       read_lock(&tasklist_lock);
+       leader = top = top->group_leader;
+down:
+       for_each_thread(leader, parent) {
+               list_for_each_entry(child, &parent->children, sibling) {
+                       res = visitor(child, data);
+                       if (res) {
+                               if (res < 0)
+                                       goto out;
+                               leader = child;
+                               goto down;
+                       }
+up:
+                       ;
+               }
+       }
+
+       if (leader != top) {
+               child = leader;
+               parent = child->real_parent;
+               leader = parent->group_leader;
+               goto up;
+       }
+out:
+       read_unlock(&tasklist_lock);
+}
+
 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
 #define ARCH_MIN_MMSTRUCT_ALIGN 0
 #endif