Added thread::io_priority field and functions to get/set it.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@27247 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/thread.h

@@ -48,6 +48,9 @@ int32 thread_used_threads(void);
 
 const char* thread_state_to_text(struct thread* thread, int32 state);
 
+int32 thread_get_io_priority(thread_id id);
+void thread_set_io_priority(int32 priority);
+
 #define thread_get_current_thread arch_thread_get_current_thread
 
 struct thread *thread_get_thread_struct(thread_id id);

headers/private/kernel/thread_types.h

@@ -240,6 +240,7 @@ struct thread {
 	char			name[B_OS_NAME_LENGTH];
 	int32			priority;
 	int32			next_priority;
+	int32			io_priority;
 	int32			state;
 	int32			next_state;
 	struct cpu_ent	*cpu;

src/system/kernel/thread.cpp

@@ -234,6 +234,7 @@ create_thread_struct(struct thread *inthread, const char *name,
 	thread->team_next = NULL;
 	thread->queue_next = NULL;
 	thread->priority = thread->next_priority = -1;
+	thread->io_priority = -1;
 	thread->args1 = NULL;  thread->args2 = NULL;
 	thread->alarm.period = 0;
 	reset_signals(thread);
@@ -1991,6 +1992,37 @@ thread_state_to_text(struct thread* thread, int32 state)
 }
 
 
+int32
+thread_get_io_priority(thread_id id)
+{
+	// take a shortcut, if it is the current thread
+	struct thread* thread = thread_get_current_thread();
+	int32 priority;
+	if (id == thread->id) {
+		int32 priority = thread->io_priority;
+		return priority < 0 ? thread->priority : priority;
+	}
+
+	// not the current thread -- get it
+	InterruptsSpinLocker locker(gThreadSpinlock);
+
+	thread = thread_get_thread_struct_locked(id);
+	if (thread == NULL)
+		return B_BAD_THREAD_ID;
+
+	priority = thread->io_priority;
+	return priority < 0 ? thread->priority : priority;
+}
+
+
+void
+thread_set_io_priority(int32 priority)
+{
+	struct thread* thread = thread_get_current_thread();
+	thread->io_priority = priority;
+}
+
+
 status_t
 thread_init(kernel_args *args)
 {