block: Generalize get_current_ioprio() for any task

get_current_ioprio() operates only on current task. We will need the
same functionality for other tasks as well. Generalize
get_current_ioprio() for that and also move the bulk out of the header
file because it is large enough.

Reviewed-by: Damien Le Moal <[e-mail]>
Tested-by: Damien Le Moal <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

block/ioprio.c

···
 	return ret;
 }
 
+/*
+ * If the task has set an I/O priority, use that. Otherwise, return
+ * the default I/O priority.
+ *
+ * Expected to be called for current task or with task_lock() held to keep
+ * io_context stable.
+ */
+int __get_task_ioprio(struct task_struct *p)
+{
+	struct io_context *ioc = p->io_context;
+	int prio;
+
+	if (p != current)
+		lockdep_assert_held(&p->alloc_lock);
+	if (ioc)
+		prio = ioc->ioprio;
+	else
+		prio = IOPRIO_DEFAULT;
+
+	if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
+		prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(p),
+					 task_nice_ioprio(p));
+	return prio;
+}
+EXPORT_SYMBOL_GPL(__get_task_ioprio);
+
 static int get_task_ioprio(struct task_struct *p)
 {
 	int ret;

include/linux/ioprio.h

···
 		return IOPRIO_CLASS_BE;
 }
 
-/*
- * If the calling process has set an I/O priority, use that. Otherwise, return
- * the default I/O priority.
- */
+#ifdef CONFIG_BLOCK
+int __get_task_ioprio(struct task_struct *p);
+#else
+static inline int __get_task_ioprio(struct task_struct *p)
+{
+	return IOPRIO_DEFAULT;
+}
+#endif /* CONFIG_BLOCK */
+
 static inline int get_current_ioprio(void)
 {
-	struct io_context *ioc = current->io_context;
-	int prio;
-
-	if (ioc)
-		prio = ioc->ioprio;
-	else
-		prio = IOPRIO_DEFAULT;
-
-	if (IOPRIO_PRIO_CLASS(prio) == IOPRIO_CLASS_NONE)
-		prio = IOPRIO_PRIO_VALUE(task_nice_ioclass(current),
-					 task_nice_ioprio(current));
-	return prio;
+	return __get_task_ioprio(current);
 }
 
 /*