selftests: ublk: add test for covering UBLK_AUTO_BUF_REG_FALLBACK

Add test for covering UBLK_AUTO_BUF_REG_FALLBACK:

- pass '--auto_zc_fallback' to null target, which requires both F_AUTO_BUF_REG
and F_SUPPORT_ZERO_COPY for handling UBLK_AUTO_BUF_REG_FALLBACK

- add ->buf_index() method for returning invalid buffer index to trigger
UBLK_AUTO_BUF_REG_FALLBACK

- add generic_09 for running the test

- add --auto_zc_fallback test in stress_03/stress_04/stress_05

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250520045455.515691-7-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

tools/testing/selftests/ublk/Makefile

@@ -16,6 +16,7 @@ TEST_PROGS += test_generic_06.sh
 TEST_PROGS += test_generic_07.sh
 
 TEST_PROGS += test_generic_08.sh
+TEST_PROGS += test_generic_09.sh
 
 TEST_PROGS += test_null_01.sh
 TEST_PROGS += test_null_02.sh

tools/testing/selftests/ublk/fault_inject.c

@@ -16,6 +16,11 @@ static int ublk_fault_inject_tgt_init(const struct dev_ctx *ctx,
 	const struct ublksrv_ctrl_dev_info *info = &dev->dev_info;
 	unsigned long dev_size = 250UL << 30;
 
+	if (ctx->auto_zc_fallback) {
+		ublk_err("%s: not support auto_zc_fallback\n", __func__);
+		return -EINVAL;
+	}
+
 	dev->tgt.dev_size = dev_size;
 	dev->tgt.params = (struct ublk_params) {
 		.types = UBLK_PARAM_TYPE_BASIC,

tools/testing/selftests/ublk/file_backed.c

@@ -149,6 +149,11 @@ static int ublk_loop_tgt_init(const struct dev_ctx *ctx, struct ublk_dev *dev)
 		},
 	};
 
+	if (ctx->auto_zc_fallback) {
+		ublk_err("%s: not support auto_zc_fallback\n", __func__);
+		return -EINVAL;
+	}
+
 	ret = backing_file_tgt_init(dev);
 	if (ret)
 		return ret;

tools/testing/selftests/ublk/kublk.c

@@ -405,7 +405,7 @@ static void ublk_queue_deinit(struct ublk_queue *q)
 		free(q->ios[i].buf_addr);
 }
 
-static int ublk_queue_init(struct ublk_queue *q)
+static int ublk_queue_init(struct ublk_queue *q, unsigned extra_flags)
 {
 	struct ublk_dev *dev = q->dev;
 	int depth = dev->dev_info.queue_depth;
@@ -427,6 +427,7 @@ static int ublk_queue_init(struct ublk_queue *q)
 		if (dev->dev_info.flags & UBLK_F_AUTO_BUF_REG)
 			q->state |= UBLKSRV_AUTO_BUF_REG;
 	}
+	q->state |= extra_flags;
 
 	cmd_buf_size = ublk_queue_cmd_buf_sz(q);
 	off = UBLKSRV_CMD_BUF_OFFSET + q->q_id * ublk_queue_max_cmd_buf_sz();
@@ -528,14 +529,19 @@ static void ublk_dev_unprep(struct ublk_dev *dev)
 	close(dev->fds[0]);
 }
 
-static void ublk_set_auto_buf_reg(struct io_uring_sqe *sqe,
-				  unsigned short buf_idx,
-				  unsigned char flags)
+static void ublk_set_auto_buf_reg(const struct ublk_queue *q,
+				  struct io_uring_sqe *sqe,
+				  unsigned short tag)
 {
-	struct ublk_auto_buf_reg buf = {
-		.index = buf_idx,
-		.flags = flags,
-	};
+	struct ublk_auto_buf_reg buf = {};
+
+	if (q->tgt_ops->buf_index)
+		buf.index = q->tgt_ops->buf_index(q, tag);
+	else
+		buf.index = tag;
+
+	if (q->state & UBLKSRV_AUTO_BUF_REG_FALLBACK)
+		buf.flags = UBLK_AUTO_BUF_REG_FALLBACK;
 
 	sqe->addr = ublk_auto_buf_reg_to_sqe_addr(&buf);
 }
@@ -595,7 +601,7 @@ int ublk_queue_io_cmd(struct ublk_queue *q, struct ublk_io *io, unsigned tag)
 		cmd->addr	= 0;
 
 	if (q->state & UBLKSRV_AUTO_BUF_REG)
-		ublk_set_auto_buf_reg(sqe[0], tag, 0);
+		ublk_set_auto_buf_reg(q, sqe[0], tag);
 
 	user_data = build_user_data(tag, _IOC_NR(cmd_op), 0, 0);
 	io_uring_sqe_set_data64(sqe[0], user_data);
@@ -747,6 +753,7 @@ struct ublk_queue_info {
 	struct ublk_queue 	*q;
 	sem_t 			*queue_sem;
 	cpu_set_t 		*affinity;
+	unsigned char 		auto_zc_fallback;
 };
 
 static void *ublk_io_handler_fn(void *data)
@@ -754,9 +761,13 @@ static void *ublk_io_handler_fn(void *data)
 	struct ublk_queue_info *info = data;
 	struct ublk_queue *q = info->q;
 	int dev_id = q->dev->dev_info.dev_id;
+	unsigned extra_flags = 0;
 	int ret;
 
-	ret = ublk_queue_init(q);
+	if (info->auto_zc_fallback)
+		extra_flags = UBLKSRV_AUTO_BUF_REG_FALLBACK;
+
+	ret = ublk_queue_init(q, extra_flags);
 	if (ret) {
 		ublk_err("ublk dev %d queue %d init queue failed\n",
 				dev_id, q->q_id);
@@ -849,6 +860,7 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev)
 		qinfo[i].q = &dev->q[i];
 		qinfo[i].queue_sem = &queue_sem;
 		qinfo[i].affinity = &affinity_buf[i];
+		qinfo[i].auto_zc_fallback = ctx->auto_zc_fallback;
 		pthread_create(&dev->q[i].thread, NULL,
 				ublk_io_handler_fn,
 				&qinfo[i]);
@@ -1264,7 +1276,7 @@ static void __cmd_create_help(char *exe, bool recovery)
 
 	printf("%s %s -t [null|loop|stripe|fault_inject] [-q nr_queues] [-d depth] [-n dev_id]\n",
 			exe, recovery ? "recover" : "add");
-	printf("\t[--foreground] [--quiet] [-z] [--auto_zc] [--debug_mask mask] [-r 0|1 ] [-g]\n");
+	printf("\t[--foreground] [--quiet] [-z] [--auto_zc] [--auto_zc_fallback] [--debug_mask mask] [-r 0|1 ] [-g]\n");
 	printf("\t[-e 0|1 ] [-i 0|1]\n");
 	printf("\t[target options] [backfile1] [backfile2] ...\n");
 	printf("\tdefault: nr_queues=2(max 32), depth=128(max 1024), dev_id=-1(auto allocation)\n");
@@ -1319,7 +1331,8 @@ int main(int argc, char *argv[])
 		{ "recovery_fail_io",	1,	NULL, 'e'},
 		{ "recovery_reissue",	1,	NULL, 'i'},
 		{ "get_data",		1,	NULL, 'g'},
-		{ "auto_zc",		0,	NULL,  0},
+		{ "auto_zc",		0,	NULL,  0 },
+		{ "auto_zc_fallback", 	0,	NULL,  0 },
 		{ 0, 0, 0, 0 }
 	};
 	const struct ublk_tgt_ops *ops = NULL;
@@ -1390,6 +1403,8 @@ int main(int argc, char *argv[])
 				ctx.fg = 1;
 			if (!strcmp(longopts[option_idx].name, "auto_zc"))
 				ctx.flags |= UBLK_F_AUTO_BUF_REG;
+			if (!strcmp(longopts[option_idx].name, "auto_zc_fallback"))
+				ctx.auto_zc_fallback = 1;
 			break;
 		case '?':
 			/*
@@ -1413,6 +1428,16 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	/* auto_zc_fallback depends on F_AUTO_BUF_REG & F_SUPPORT_ZERO_COPY */
+	if (ctx.auto_zc_fallback &&
+	    !((ctx.flags & UBLK_F_AUTO_BUF_REG) &&
+		    (ctx.flags & UBLK_F_SUPPORT_ZERO_COPY))) {
+		ublk_err("%s: auto_zc_fallback is set but neither "
+				"F_AUTO_BUF_REG nor F_SUPPORT_ZERO_COPY is enabled\n",
+					__func__);
+		return -EINVAL;
+	}
+
 	i = optind;
 	while (i < argc && ctx.nr_files < MAX_BACK_FILES) {
 		ctx.files[ctx.nr_files++] = argv[i++];

tools/testing/selftests/ublk/kublk.h

@@ -84,6 +84,7 @@ struct dev_ctx {
 	unsigned int	all:1;
 	unsigned int	fg:1;
 	unsigned int	recovery:1;
+	unsigned int	auto_zc_fallback:1;
 
 	int _evtfd;
 	int _shmid;
@@ -141,6 +142,9 @@ struct ublk_tgt_ops {
 	 */
 	void (*parse_cmd_line)(struct dev_ctx *ctx, int argc, char *argv[]);
 	void (*usage)(const struct ublk_tgt_ops *ops);
+
+	/* return buffer index for UBLK_F_AUTO_BUF_REG */
+	unsigned short (*buf_index)(const struct ublk_queue *, int tag);
 };
 
 struct ublk_tgt {
@@ -170,6 +174,7 @@ struct ublk_queue {
 #define UBLKSRV_NO_BUF		(1U << 2)
 #define UBLKSRV_ZC		(1U << 3)
 #define UBLKSRV_AUTO_BUF_REG		(1U << 4)
+#define UBLKSRV_AUTO_BUF_REG_FALLBACK	(1U << 5)
 	unsigned state;
 	pid_t tid;
 	pthread_t thread;
@@ -205,6 +210,12 @@ struct ublk_dev {
 extern unsigned int ublk_dbg_mask;
 extern int ublk_queue_io_cmd(struct ublk_queue *q, struct ublk_io *io, unsigned tag);
 
+
+static inline int ublk_io_auto_zc_fallback(const struct ublksrv_io_desc *iod)
+{
+	return !!(iod->op_flags & UBLK_IO_F_NEED_REG_BUF);
+}
+
 static inline int is_target_io(__u64 user_data)
 {
 	return (user_data & (1ULL << 63)) != 0;

tools/testing/selftests/ublk/null.c

@@ -116,7 +116,7 @@ static int ublk_null_queue_io(struct ublk_queue *q, int tag)
 	unsigned zc = ublk_queue_use_zc(q);
 	int queued;
 
-	if (auto_zc)
+	if (auto_zc && !ublk_io_auto_zc_fallback(iod))
 		queued = null_queue_auto_zc_io(q, tag);
 	else if (zc)
 		queued = null_queue_zc_io(q, tag);
@@ -128,9 +128,21 @@ static int ublk_null_queue_io(struct ublk_queue *q, int tag)
 	return 0;
 }
 
+/*
+ * return invalid buffer index for triggering auto buffer register failure,
+ * then UBLK_IO_RES_NEED_REG_BUF handling is covered
+ */
+static unsigned short ublk_null_buf_index(const struct ublk_queue *q, int tag)
+{
+	if (q->state & UBLKSRV_AUTO_BUF_REG_FALLBACK)
+		return (unsigned short)-1;
+	return tag;
+}
+
 const struct ublk_tgt_ops null_tgt_ops = {
 	.name = "null",
 	.init_tgt = ublk_null_tgt_init,
 	.queue_io = ublk_null_queue_io,
 	.tgt_io_done = ublk_null_io_done,
+	.buf_index = ublk_null_buf_index,
 };

tools/testing/selftests/ublk/stripe.c

@@ -288,6 +288,11 @@ static int ublk_stripe_tgt_init(const struct dev_ctx *ctx, struct ublk_dev *dev)
 	loff_t bytes = 0;
 	int ret, i, mul = 1;
 
+	if (ctx->auto_zc_fallback) {
+		ublk_err("%s: not support auto_zc_fallback\n", __func__);
+		return -EINVAL;
+	}
+
 	if ((chunk_size & (chunk_size - 1)) || !chunk_size) {
 		ublk_err("invalid chunk size %u\n", chunk_size);
 		return -EINVAL;

tools/testing/selftests/ublk/test_generic_09.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+. "$(cd "$(dirname "$0")" && pwd)"/test_common.sh
+
+TID="generic_09"
+ERR_CODE=0
+
+if ! _have_feature "AUTO_BUF_REG"; then
+	exit "$UBLK_SKIP_CODE"
+fi
+
+if ! _have_program fio; then
+	exit "$UBLK_SKIP_CODE"
+fi
+
+_prep_test "null" "basic IO test"
+
+dev_id=$(_add_ublk_dev -t null -z --auto_zc --auto_zc_fallback)
+_check_add_dev $TID $?
+
+# run fio over the two disks
+fio --name=job1 --filename=/dev/ublkb"${dev_id}" --ioengine=libaio --rw=readwrite --iodepth=32 --size=256M > /dev/null 2>&1
+ERR_CODE=$?
+
+_cleanup_test "null"
+
+_show_result $TID $ERR_CODE

tools/testing/selftests/ublk/test_stress_03.sh

@@ -37,6 +37,7 @@ if _have_feature "AUTO_BUF_REG"; then
 	ublk_io_and_remove 8G -t null -q 4 --auto_zc &
 	ublk_io_and_remove 256M -t loop -q 4 --auto_zc "${UBLK_BACKFILES[0]}" &
 	ublk_io_and_remove 256M -t stripe -q 4 --auto_zc "${UBLK_BACKFILES[1]}" "${UBLK_BACKFILES[2]}" &
+	ublk_io_and_remove 8G -t null -q 4 -z --auto_zc --auto_zc_fallback &
 fi
 wait
 

tools/testing/selftests/ublk/test_stress_04.sh

@@ -36,6 +36,7 @@ if _have_feature "AUTO_BUF_REG"; then
 	ublk_io_and_kill_daemon 8G -t null -q 4 --auto_zc &
 	ublk_io_and_kill_daemon 256M -t loop -q 4 --auto_zc "${UBLK_BACKFILES[0]}" &
 	ublk_io_and_kill_daemon 256M -t stripe -q 4 --auto_zc "${UBLK_BACKFILES[1]}" "${UBLK_BACKFILES[2]}" &
+	ublk_io_and_kill_daemon 8G -t null -q 4 -z --auto_zc --auto_zc_fallback &
 fi
 wait
 

tools/testing/selftests/ublk/test_stress_05.sh

@@ -64,6 +64,7 @@ if _have_feature "AUTO_BUF_REG"; then
 	for reissue in $(seq 0 1); do
 		ublk_io_and_remove 8G -t null -q 4 -g --auto_zc -r 1 -i "$reissue" &
 		ublk_io_and_remove 256M -t loop -q 4 -g --auto_zc -r 1 -i "$reissue" "${UBLK_BACKFILES[1]}" &
+		ublk_io_and_remove 8G -t null -q 4 -g -z --auto_zc --auto_zc_fallback -r 1 -i "$reissue" &
 		wait
 	done
 fi