linux-kernel - [PATCH 14/20] selftests: ublk: add utility to get block device metadata size

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Message-ID: <20251217053455.281509-15-csander@purestorage.com>
Date: Tue, 16 Dec 2025 22:34:48 -0700
From: Caleb Sander Mateos <csander@...estorage.com>
To: Ming Lei <ming.lei@...hat.com>,
	Jens Axboe <axboe@...nel.dk>,
	Shuah Khan <shuah@...nel.org>
Cc: linux-block@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Stanley Zhang <stazhang@...estorage.com>,
	Uday Shankar <ushankar@...estorage.com>,
	Caleb Sander Mateos <csander@...estorage.com>
Subject: [PATCH 14/20] selftests: ublk: add utility to get block device metadata size

Some block device integrity parameters are available in sysfs, but
others are only accessible using the FS_IOC_GETLBMD_CAP ioctl. Add a
metadata_size utility program to print out the logical block metadata
size, PI offset, and PI size within the metadata. Example output:
$ metadata_size /dev/ublkb0
metadata_size: 64
pi_offset: 56
pi_tuple_size: 8

Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
---
 tools/testing/selftests/ublk/Makefile        |  4 +--
 tools/testing/selftests/ublk/metadata_size.c | 36 ++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/ublk/metadata_size.c

diff --git a/tools/testing/selftests/ublk/Makefile b/tools/testing/selftests/ublk/Makefile
index 837977b62417..0f6abb95c87a 100644
--- a/tools/testing/selftests/ublk/Makefile
+++ b/tools/testing/selftests/ublk/Makefile
@@ -46,14 +46,14 @@ TEST_PROGS += test_stress_03.sh
 TEST_PROGS += test_stress_04.sh
 TEST_PROGS += test_stress_05.sh
 TEST_PROGS += test_stress_06.sh
 TEST_PROGS += test_stress_07.sh
 
-TEST_GEN_PROGS_EXTENDED = kublk
+TEST_GEN_PROGS_EXTENDED = kublk metadata_size
 
 include ../lib.mk
 
-$(TEST_GEN_PROGS_EXTENDED): kublk.c null.c file_backed.c common.c stripe.c \
+$(OUTPUT)/kublk: kublk.c null.c file_backed.c common.c stripe.c \
 	fault_inject.c
 
 check:
 	shellcheck -x -f gcc *.sh
diff --git a/tools/testing/selftests/ublk/metadata_size.c b/tools/testing/selftests/ublk/metadata_size.c
new file mode 100644
index 000000000000..76ecddf04d25
--- /dev/null
+++ b/tools/testing/selftests/ublk/metadata_size.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <stdio.h>
+#include <sys/ioctl.h>
+
+int main(int argc, char **argv)
+{
+	struct logical_block_metadata_cap cap = {};
+	const char *filename;
+	int fd;
+	int result;
+
+	if (argc != 2) {
+		fprintf(stderr, "Usage: %s BLOCK_DEVICE\n", argv[0]);
+		return 1;
+	}
+
+	filename = argv[1];
+	fd = open(filename, O_RDONLY);
+	if (fd < 0) {
+		perror(filename);
+		return 1;
+	}
+
+	result = ioctl(fd, FS_IOC_GETLBMD_CAP, &cap);
+	if (result < 0) {
+		perror("ioctl");
+		return 1;
+	}
+
+	printf("metadata_size: %u\n", cap.lbmd_size);
+	printf("pi_offset: %u\n", cap.lbmd_pi_offset);
+	printf("pi_tuple_size: %u\n", cap.lbmd_pi_size);
+	return 0;
+}
-- 
2.45.2