fs, proc: introduce /proc/<pid>/task/<tid>/children entry

[GitHub/mt8127/android_kernel_alcatel_ttab.git] / fs / proc / array.c

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 3a26d23420cc00d0f5f2b8d974c073f76de6ccd4..62887e39a2de423e5416f1092b4458f290d31d5a 100644 (file)
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -565,3 +565,126 @@ int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
 
        return 0;
 }
+
+#ifdef CONFIG_CHECKPOINT_RESTORE
+static struct pid *
+get_children_pid(struct inode *inode, struct pid *pid_prev, loff_t 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;
+
+       /*
+        * 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 &&
+                   !(list_empty(&task->sibling))) {
+                       if (list_is_last(&task->sibling, &start->children))
+                               goto out;
+                       task = list_first_entry(&task->sibling,
+                                               struct task_struct, sibling);
+                       pid = get_pid(task_pid(task));
+                       goto out;
+               }
+       }
+
+       /*
+        * Slow search case.
+        *
+        * We might miss some children here if children
+        * are exited while we were not holding the lock,
+        * but it was never promised to be accurate that
+        * much.
+        *
+        * "Just suppose that the parent sleeps, but N children
+        *  exit after we printed their tids. Now the slow paths
+        *  skips N extra children, we miss N tasks." (c)
+        *
+        * 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;
+               }
+       }
+
+out:
+       read_unlock(&tasklist_lock);
+       return pid;
+}
+
+static int children_seq_show(struct seq_file *seq, void *v)
+{
+       struct inode *inode = seq->private;
+       pid_t pid;
+
+       pid = pid_nr_ns(v, inode->i_sb->s_fs_info);
+       return seq_printf(seq, "%d ", pid);
+}
+
+static void *children_seq_start(struct seq_file *seq, loff_t *pos)
+{
+       return get_children_pid(seq->private, NULL, *pos);
+}
+
+static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+       struct pid *pid;
+
+       pid = get_children_pid(seq->private, v, *pos + 1);
+       put_pid(v);
+
+       ++*pos;
+       return pid;
+}
+
+static void children_seq_stop(struct seq_file *seq, void *v)
+{
+       put_pid(v);
+}
+
+static const struct seq_operations children_seq_ops = {
+       .start  = children_seq_start,
+       .next   = children_seq_next,
+       .stop   = children_seq_stop,
+       .show   = children_seq_show,
+};
+
+static int children_seq_open(struct inode *inode, struct file *file)
+{
+       struct seq_file *m;
+       int ret;
+
+       ret = seq_open(file, &children_seq_ops);
+       if (ret)
+               return ret;
+
+       m = file->private_data;
+       m->private = inode;
+
+       return ret;
+}
+
+int children_seq_release(struct inode *inode, struct file *file)
+{
+       seq_release(inode, file);
+       return 0;
+}
+
+const struct file_operations proc_tid_children_operations = {
+       .open    = children_seq_open,
+       .read    = seq_read,
+       .llseek  = seq_lseek,
+       .release = children_seq_release,
+};
+#endif /* CONFIG_CHECKPOINT_RESTORE */