Re: [PATCH 1/3] Introduce the dummy_pid

Randy Dunlap
2007-10-03T18:11:42Z

On Wed, 03 Oct 2007 18:19:01 +0400 Pavel Emelyanov wrote:

> This is a pid which is attached to tasks when they detach
> their pids. This is done in detach_pid() and transfer_pid().
> The pid_alive() check is changed to reflect this fact.
>
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
>
> ---
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 4f21af1..e17b8f8 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1286,9 +1286,11 @@ static inline pid_t task_ppid_nr_ns(stru
> * If pid_alive fails, then pointers within the task structure
> * can be stale and must not be dereferenced.
> */
> +extern struct pid dummy_pid;
> +
> static inline int pid_alive(struct task_struct *p)
> {
> - return p->pids[PIDTYPE_PID].pid != NULL;
> + return p->pids[PIDTYPE_PID].pid != &dummy_pid;
> }
>
> /**
> diff --git a/kernel/pid.c b/kernel/pid.c
> index d7388d7..b7a11cf 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -81,6 +81,17 @@ struct pid_namespace init_pid_ns = {
> };
> EXPORT_SYMBOL_GPL(init_pid_ns);
>
> +struct pid dummy_pid = {
> + .count = ATOMIC_INIT(1),
> + .numbers = { {
> + .nr = 0, /* this is what pid_nr will return
> + * for tasks with no pids
> + */
> + .ns = &init_pid_ns,
> + }, }
> +};
> +EXPORT_SYMBOL(dummy_pid);

Why is the EXPORT_SYMBOL() needed?
IOW, is some loadable module going to use this?

---
~Randy