selftests: ublk: add kernel selftests for ublk

Both ublk driver and userspace heavily depends on io_uring subsystem,
and tools/testing/selftests/ should be the best place for holding this
cross-subsystem tests.

Add basic read/write IO test over this ublk null disk, and make sure ublk
working.

More tests will be added.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250228161919.2869102-2-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 38 insertions, 0 deletions

diff --git a/tools/testing/selftests/ublk/null.c b/tools/testing/selftests/ublk/null.c
new file mode 100644
index 000000000000..b6ef16a8f514
--- /dev/null
+++ b/tools/testing/selftests/ublk/null.c
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "kublk.h"
+
+static int ublk_null_tgt_init(struct ublk_dev *dev)
+{
+	const struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
+	unsigned long dev_size = 250UL << 30;
+
+	dev->tgt.dev_size = dev_size;
+	dev->tgt.params = (struct ublk_params) {
+		.types = UBLK_PARAM_TYPE_BASIC,
+		.basic = {
+			.logical_bs_shift	= 9,
+			.physical_bs_shift	= 12,
+			.io_opt_shift		= 12,
+			.io_min_shift		= 9,
+			.max_sectors		= info->max_io_buf_bytes >> 9,
+			.dev_sectors		= dev_size >> 9,
+		},
+	};
+
+	return 0;
+}
+
+static int ublk_null_queue_io(struct ublk_queue *q, int tag)
+{
+	const struct ublksrv_io_desc *iod = ublk_get_iod(q, tag);
+
+	ublk_complete_io(q, tag, iod->nr_sectors << 9);
+	return 0;
+}
+
+const struct ublk_tgt_ops null_tgt_ops = {
+	.name = "null",
+	.init_tgt = ublk_null_tgt_init,
+	.queue_io = ublk_null_queue_io,
+};