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

[Justus Winter <4winter@informatik.uni-hamburg.de>]

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