Re: [PATCH 09/11] Task watchers: Add support for per-task watchers

[Peter Williams <pwil3058@bigpond.net.au>]

Matt Helsley wrote:
> This introduces a second, per-task, blocking notifier chain. The per-task
> chain offers watchers the chance to register with a specific task nstead of
> all tasks. It also allows the watcher to associate a block of data with the task
> by wrapping the notifier block using containerof().
> 
> Both the global, all-tasks chain and the per-task chain are called from the samefunction. The two types of chains share the same set of notification
> values, however registration functions and the registered notifier blocks must
> be separate.
> 
> These notifiers are only safe if notifier blocks are registered with the current
> task while in the context of the current task. This ensures that there are no
> races between registration, unregistration, and notification.
> 
> Signed-off-by: Matt Helsley <matthltc@us.ibm.com>
> Cc: Jes Sorensen <jes@sgi.com>
> Cc: Chandra S. Seetharaman <sekharan@us.ibm.com>
> Cc: Alan Stern <stern@rowland.harvard.edu>
[bits deleted]

> Index: linux-2.6.17-rc6-mm2/kernel/sys.c
> ===================================================================
> --- linux-2.6.17-rc6-mm2.orig/kernel/sys.c
> +++ linux-2.6.17-rc6-mm2/kernel/sys.c
> @@ -450,13 +450,41 @@ int unregister_task_watcher(struct notif
>  	return blocking_notifier_chain_unregister(&task_watchers, nb);
>  }
>  
>  EXPORT_SYMBOL_GPL(unregister_task_watcher);
>  
> +static inline int notify_per_task_watchers(unsigned int val,
> +					   struct task_struct *task)
> +{
> +	if (get_watch_event(val) != WATCH_TASK_INIT)
> +		return raw_notifier_call_chain(&task->notify, val, task);
> +	RAW_INIT_NOTIFIER_HEAD(&task->notify);
> +	if (task->real_parent)
> +		return raw_notifier_call_chain(&task->real_parent->notify,
> +		   			       val, task);
> +}

It's possible for this task to exit without returning a result.

Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce