selftests: ublk: specify io_cmd_buf pointer type

Matching the ublk driver, change the type of io_cmd_buf from char * to
struct ublksrv_io_desc *.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250328194230.2726862-3-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/testing/selftests/ublk/kublk.c

@@ -322,7 +322,7 @@ static int ublk_queue_init(struct ublk_queue *q)
 
 	cmd_buf_size = ublk_queue_cmd_buf_sz(q);
 	off = UBLKSRV_CMD_BUF_OFFSET + q->q_id * ublk_queue_max_cmd_buf_sz();
-	q->io_cmd_buf = (char *)mmap(0, cmd_buf_size, PROT_READ,
+	q->io_cmd_buf = mmap(0, cmd_buf_size, PROT_READ,
 			MAP_SHARED | MAP_POPULATE, dev->fds[0], off);
 	if (q->io_cmd_buf == MAP_FAILED) {
 		ublk_err("ublk dev %d queue %d map io_cmd_buf failed %m\n",

tools/testing/selftests/ublk/kublk.h

@@ -128,7 +128,7 @@ struct ublk_queue {
 	unsigned int io_inflight;
 	struct ublk_dev *dev;
 	const struct ublk_tgt_ops *tgt_ops;
-	char *io_cmd_buf;
+	struct ublksrv_io_desc *io_cmd_buf;
 	struct io_uring ring;
 	struct ublk_io ios[UBLK_QUEUE_DEPTH];
 #define UBLKSRV_QUEUE_STOPPING	(1U << 0)
@@ -302,7 +302,7 @@ static inline void ublk_mark_io_done(struct ublk_io *io, int res)
 
 static inline const struct ublksrv_io_desc *ublk_get_iod(const struct ublk_queue *q, int tag)
 {
-	return (struct ublksrv_io_desc *)&(q->io_cmd_buf[tag * sizeof(struct ublksrv_io_desc)]);
+	return &q->io_cmd_buf[tag];
 }
 
 static inline void ublk_set_sqe_cmd_op(struct io_uring_sqe *sqe, __u32 cmd_op)