[PATCH 1/2] kern: track the parent of a task

[Justus Winter]

Align Machs model of a task more closely with that of a Unix process
by tracking the parent task.

XXX: Not sure if it's worth keeping a real reference to the parent
since that way we prevent the parent task from being collected if it
dies before the child does.

* kern/task.h (struct task): Add field parent_task.
* kern/task.c (task_create): Keep a reference to the parent task.
(task_deallocate): Dereference the parent task.
---
 kern/task.c |    3 +++
 kern/task.h |    1 +
 2 files changed, 4 insertions(+)

diff --git a/kern/task.c b/kern/task.c
index 114dd31..0c0be99 100644
--- a/kern/task.c
+++ b/kern/task.c
@@ -105,6 +105,8 @@ kern_return_t task_create(
        simple_lock_init(&new_task->lock);
        queue_init(&new_task->thread_list);
        new_task->suspend_count = 0;
+       task_reference(parent_task);
+       new_task->parent_task = parent_task;
        new_task->active = TRUE;
        new_task->user_stop_count = 0;
        new_task->thread_count = 0;
@@ -206,6 +208,7 @@ void task_deallocate(
        pset_deallocate(pset);
        vm_map_deallocate(task->map);
        is_release(task->itk_space);
+       task_deallocate(task->parent_task);
        kmem_cache_free(&task_cache, (vm_offset_t) task);
 }
 
diff --git a/kern/task.h b/kern/task.h
index 9bfea57..c8d9f3d 100644
--- a/kern/task.h
+++ b/kern/task.h
@@ -58,6 +58,7 @@ struct task {
        vm_map_t        map;            /* Address space description */
        queue_chain_t   pset_tasks;     /* list of tasks assigned to pset */
        int             suspend_count;  /* Internal scheduling only */
+       task_t          parent_task;    /* Parent of the task */
 
        /* Thread information */
        queue_head_t    thread_list;    /* list of threads */
-- 
1.7.10.4