diff options
author | Cyrill Gorcunov <gorcunov@openvz.org> | 2012-05-31 16:26:43 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-05-31 17:49:32 -0700 |
commit | 818411616baf46ceba0cff6f05af3a9b294734f7 (patch) | |
tree | b6e338e20d4a45b6a05ffa37e6af33e0cc1b50c0 /fs/proc/array.c | |
parent | 98ed57eef9f67dfe541be0bca34660ffc88365b2 (diff) |
fs, proc: introduce /proc/<pid>/task/<tid>/children entry
When we do checkpoint of a task we need to know the list of children the
task, has but there is no easy and fast way to generate reverse
parent->children chain from arbitrary <pid> (while a parent pid is
provided in "PPid" field of /proc/<pid>/status).
So instead of walking over all pids in the system (creating one big
process tree in memory, just to figure out which children a task has) --
we add explicit /proc/<pid>/task/<tid>/children entry, because the kernel
already has this kind of information but it is not yet exported.
This is a first level children, not the whole process tree.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/proc/array.c')
-rw-r--r-- | fs/proc/array.c | 123 |
1 files changed, 123 insertions, 0 deletions
diff --git a/fs/proc/array.c b/fs/proc/array.c index 3a26d23420c..62887e39a2d 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 */ |