scsi: block: ioprio: Clean up interface definition

The I/O priority user interface defines the 16-bits ioprio values as the
combination of the upper 3-bits for an I/O priority class and the lower
13-bits as priority data. However, the kernel only uses the lower 3-bits of
the priority data to define priority levels for the RT and BE priority
classes. The data part of an ioprio value is completely ignored for the
IDLE and NONE classes. This is enforced by checks done in
ioprio_check_cap(), which is called for all paths that allow defining an
I/O priority for I/Os: the per-context ioprio_set() system call, aio
interface and io_uring interface.

Clarify this fact in the uapi ioprio.h header file and introduce the
IOPRIO_PRIO_LEVEL_MASK and IOPRIO_PRIO_LEVEL() macros for users to define
and get priority levels in an ioprio value. The coarser macro
IOPRIO_PRIO_DATA() is retained for backward compatibility with old
applications already using it. There is no functional change introduced
with this.

In-kernel users of the IOPRIO_PRIO_DATA() macro which are explicitly
handling I/O priority data as a priority level are modified to use the new
IOPRIO_PRIO_LEVEL() macro without any functional change. Since f2fs is the
only user of this macro not explicitly using that value as a priority
level, it is left unchanged.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20230511011356.227789-2-nks@flawful.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 3164e3177965..3067b75f3fd0 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5524,16 +5524,16 @@ bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
 		bfqq->new_ioprio_class = task_nice_ioclass(tsk);
 		break;
 	case IOPRIO_CLASS_RT:
-		bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
+		bfqq->new_ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
 		bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
 		break;
 	case IOPRIO_CLASS_BE:
-		bfqq->new_ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
+		bfqq->new_ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
 		bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
 		break;
 	case IOPRIO_CLASS_IDLE:
 		bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
-		bfqq->new_ioprio = 7;
+		bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
 		break;
 	}
 
@@ -5830,7 +5830,7 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
 				       struct bfq_io_cq *bic,
 				       bool respawn)
 {
-	const int ioprio = IOPRIO_PRIO_DATA(bic->ioprio);
+	const int ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
 	const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
 	struct bfq_queue **async_bfqq = NULL;
 	struct bfq_queue *bfqq;