lkml.org 
[lkml]   [2006]   [Jun]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [Lse-tech] [PATCH 09/11] Task watchers: Add support for per-task watchers
    From
    Date
    On Tue, 2006-06-20 at 15:28 +1000, Peter Williams wrote:
    > 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.

    Assuming you meant s/task/function/:

    In the common case this will return a result because most tasks have a
    real parent. The only exception should be the init task. However, the
    init task does not "fork" from another task so this function will never
    get called with WATCH_TASK_INIT and the init task.

    This means that if one wants to use per-task watchers to associate data
    and a function call with *every* task, special care will need to be
    taken to register with the init task.

    > Peter

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-06-21 01:05    [W:0.027 / U:185.404 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site