[PATCH 01/15] proc: pick out a function to iterate task children

[Andrey Vagin]

This function will be used in task_diag.

Signed-off-by: Andrey Vagin <ava...@openvz.org>
---
 fs/proc/array.c    | 53 +++++++++++++++++++++++++++++++++--------------------
 fs/proc/internal.h |  3 +++
 2 files changed, 36 insertions(+), 20 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index b6c00ce..3eceab1 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -593,31 +593,25 @@ int proc_pid_statm(struct seq_file *m, struct 
pid_namespace *ns,
 }
 
 #ifdef CONFIG_PROC_CHILDREN
-static struct pid *
-get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t pos)
+struct task_struct *
+task_next_child(struct task_struct *parent, struct task_struct *prev, unsigned 
int pos)
 {
-       struct task_struct *start, *task;
-       struct pid *pid = NULL;
-
-       read_lock(&tasklist_lock);
-
-       start = pid_task(proc_pid(inode), PIDTYPE_PID);
-       if (!start)
-               goto out;
+       struct task_struct *task;
 
        /*
         * Lets try to continue searching first, this gives
         * us significant speedup on children-rich processes.
         */
-       if (pid_prev) {
-               task = pid_task(pid_prev, PIDTYPE_PID);
-               if (task && task->real_parent == start &&
+       if (prev) {
+               task = prev;
+               if (task && task->real_parent == parent &&
                    !(list_empty(&task->sibling))) {
-                       if (list_is_last(&task->sibling, &start->children))
+                       if (list_is_last(&task->sibling, &parent->children)) {
+                               task = NULL;
                                goto out;
+                       }
                        task = list_first_entry(&task->sibling,
                                                struct task_struct, sibling);
-                       pid = get_pid(task_pid(task));
                        goto out;
                }
        }
@@ -637,12 +631,31 @@ get_children_pid(struct inode *inode, struct pid 
*pid_prev, loff_t pos)
         * So one need to stop or freeze the leader and all
         * its children to get a precise result.
         */
-       list_for_each_entry(task, &start->children, sibling) {
-               if (pos-- == 0) {
-                       pid = get_pid(task_pid(task));
-                       break;
-               }
+       list_for_each_entry(task, &parent->children, sibling) {
+               if (pos-- == 0)
+                       goto out;
        }
+       task = NULL;
+out:
+       return task;
+}
+
+static struct pid *
+get_children_pid(struct inode *inode, struct pid *prev_pid, loff_t pos)
+{
+       struct task_struct *start, *task, *prev;
+       struct pid *pid = NULL;
+
+       read_lock(&tasklist_lock);
+       start = pid_task(proc_pid(inode), PIDTYPE_PID);
+       if (!start)
+               goto out;
+
+       prev = prev_pid ? pid_task(prev_pid, PIDTYPE_PID) : NULL;
+
+       task = task_next_child(start, prev, pos);
+       if (task)
+               pid = get_pid(task_pid(task));
 
 out:
        read_unlock(&tasklist_lock);
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index aa27810..969e05b 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -303,3 +303,6 @@ extern unsigned long task_statm(struct mm_struct *,
                                unsigned long *, unsigned long *,
                                unsigned long *, unsigned long *);
 extern void task_mem(struct seq_file *, struct mm_struct *);
+
+struct task_struct *
+task_next_child(struct task_struct *parent, struct task_struct *prev, unsigned 
int pos);
-- 
2.5.5