FreeBSD: Implement taskq_init_ent()

Previously taskq_init_ent() was an empty macro, while actual init
was done by taskq_dispatch_ent().  It could be slightly faster in
case taskq never enqueued. But without it taskq_empty_ent() relied
on the structure being zeroed by somebody else, that is not good.

As a side effect this allows the same task to be queued several
times, that is normal on FreeBSD, that may or may not get useful
here also one day.

Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Closes #15455

include/os/freebsd/spl/sys/taskq.h

@@ -82,7 +82,6 @@ typedef struct taskq_ent {
 
 #define	TASKQID_INVALID		((taskqid_t)0)
 
-#define	taskq_init_ent(x)
 extern taskq_t *system_taskq;
 /* Global dynamic task queue for long delay */
 extern taskq_t *system_delay_taskq;
@@ -93,6 +92,7 @@ extern taskqid_t taskq_dispatch_delay(taskq_t *, task_func_t, void *,
 extern void taskq_dispatch_ent(taskq_t *, task_func_t, void *, uint_t,
     taskq_ent_t *);
 extern int taskq_empty_ent(taskq_ent_t *);
+extern void taskq_init_ent(taskq_ent_t *);
 taskq_t	*taskq_create(const char *, int, pri_t, int, int, uint_t);
 taskq_t	*taskq_create_synced(const char *, int, pri_t, int, int, uint_t,
     kthread_t ***);

module/os/freebsd/spl/spl_taskq.c

@@ -480,21 +480,33 @@ void
 taskq_dispatch_ent(taskq_t *tq, task_func_t func, void *arg, uint32_t flags,
     taskq_ent_t *task)
 {
-	int prio;
-
 	/*
 	 * If TQ_FRONT is given, we want higher priority for this task, so it
 	 * can go at the front of the queue.
 	 */
-	prio = !!(flags & TQ_FRONT);
-	task->tqent_id = 0;
+	task->tqent_task.ta_priority = !!(flags & TQ_FRONT);
 	task->tqent_func = func;
 	task->tqent_arg = arg;
-
-	TASK_INIT(&task->tqent_task, prio, taskq_run_ent, task);
 	taskqueue_enqueue(tq->tq_queue, &task->tqent_task);
 }
 
+void
+taskq_init_ent(taskq_ent_t *task)
+{
+	TASK_INIT(&task->tqent_task, 0, taskq_run_ent, task);
+	task->tqent_func = NULL;
+	task->tqent_arg = NULL;
+	task->tqent_id = 0;
+	task->tqent_type = NORMAL_TASK;
+	task->tqent_rc = 0;
+}
+
+int
+taskq_empty_ent(taskq_ent_t *task)
+{
+	return (task->tqent_task.ta_pending == 0);
+}
+
 void
 taskq_wait(taskq_t *tq)
 {
@@ -521,9 +533,3 @@ taskq_wait_outstanding(taskq_t *tq, taskqid_t id __unused)
 {
 	taskqueue_drain_all(tq->tq_queue);
 }
-
-int
-taskq_empty_ent(taskq_ent_t *t)
-{
-	return (t->tqent_task.ta_pending == 0);
-}