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-rw-r--r--Documentation/filesystems/proc.txt18
-rw-r--r--fs/proc/array.c123
-rw-r--r--fs/proc/base.c3
-rw-r--r--fs/proc/internal.h1
4 files changed, 145 insertions, 0 deletions
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 912af6ce5626..d8d3f9a8e5a3 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -40,6 +40,7 @@ Table of Contents
3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
3.5 /proc/<pid>/mountinfo - Information about mounts
3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
+ 3.7 /proc/<pid>/task/<tid>/children - Information about task children
4 Configuring procfs
4.1 Mount options
@@ -1578,6 +1579,23 @@ then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
comm value.
+3.7 /proc/<pid>/task/<tid>/children - Information about task children
+-------------------------------------------------------------------------
+This file provides a fast way to retrieve first level children pids
+of a task pointed by <pid>/<tid> pair. The format is a space separated
+stream of pids.
+
+Note the "first level" here -- if a child has own children they will
+not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
+to obtain the descendants.
+
+Since this interface is intended to be fast and cheap it doesn't
+guarantee to provide precise results and some children might be
+skipped, especially if they've exited right after we printed their
+pids, so one need to either stop or freeze processes being inspected
+if precise results are needed.
+
+
------------------------------------------------------------------------------
Configuring procfs
------------------------------------------------------------------------------
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 3a26d23420cc..62887e39a2de 100644
--- 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 */
diff --git a/fs/proc/base.c b/fs/proc/base.c
index bd8b4ca6a610..616f41a7cde6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3400,6 +3400,9 @@ static const struct pid_entry tid_base_stuff[] = {
ONE("stat", S_IRUGO, proc_tid_stat),
ONE("statm", S_IRUGO, proc_pid_statm),
REG("maps", S_IRUGO, proc_tid_maps_operations),
+#ifdef CONFIG_CHECKPOINT_RESTORE
+ REG("children", S_IRUGO, proc_tid_children_operations),
+#endif
#ifdef CONFIG_NUMA
REG("numa_maps", S_IRUGO, proc_tid_numa_maps_operations),
#endif
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index a30643784db5..eca4aca5b6e2 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -54,6 +54,7 @@ extern int proc_pid_statm(struct seq_file *m, struct pid_namespace *ns,
struct pid *pid, struct task_struct *task);
extern loff_t mem_lseek(struct file *file, loff_t offset, int orig);
+extern const struct file_operations proc_tid_children_operations;
extern const struct file_operations proc_pid_maps_operations;
extern const struct file_operations proc_tid_maps_operations;
extern const struct file_operations proc_pid_numa_maps_operations;
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