[PATCH blktests 2/4] nvme/071: test that nvmet sends no data for a failed read

[Andrea Parri <parri.andrea@gmail.com>]

Issue a failing Identify into a buffer filled with a sentinel and verify
that the target transfers no data, with a successful Identify and a
namespace read as controls. The test runs on every configured transport;
only nvmet-fc failed it before the fix. Add a small helper because
nvme-cli cannot prefill the data buffer.

The test fails over fc on the unpatched kernel and passes with the fix
applied.

Assisted-by: LLM
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
---
 src/.gitignore           |  1 +
 src/Makefile             |  1 +
 src/nvme-sentinel-read.c | 89 ++++++++++++++++++++++++++++++++++++++++
 tests/nvme/071           | 80 ++++++++++++++++++++++++++++++++++++
 tests/nvme/071.out       |  2 +
 5 files changed, 173 insertions(+)
 create mode 100644 src/nvme-sentinel-read.c
 create mode 100755 tests/nvme/071
 create mode 100644 tests/nvme/071.out

diff --git a/src/.gitignore b/src/.gitignore
index e9869e172b20f..2429da9d9cf44 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -18,3 +18,4 @@
 /ioctl-lbmd-query
 /nvme-passthru-admin-uring
 /nvme-delay-ioctl
+/nvme-sentinel-read
diff --git a/src/Makefile b/src/Makefile
index dd646940fa25e..78433f0762b4a 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -24,6 +24,7 @@ C_TARGETS := \
 	mount_clear_sock \
 	nvme-delay-ioctl \
 	nvme-passthrough-meta \
+	nvme-sentinel-read \
 	ioctl-lbmd-query \
 	nbdsetsize \
 	openclose \
diff --git a/src/nvme-sentinel-read.c b/src/nvme-sentinel-read.c
new file mode 100644
index 0000000000000..dd36f283f46e2
--- /dev/null
+++ b/src/nvme-sentinel-read.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-3.0+
+// Copyright (C) 2026 Andrea Parri
+
+/*
+ * Issue an NVMe admin read command into a buffer filled with a sentinel and
+ * print the NVMe status and the number of bytes the command overwrote.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/nvme_ioctl.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#define SENTINEL	0xa5
+
+static int parse_u32(const char *s, uint32_t *val)
+{
+	unsigned long v;
+	char *end;
+
+	errno = 0;
+	v = strtoul(s, &end, 0);
+	if (errno || end == s || *end || v > UINT32_MAX)
+		return -1;
+	*val = v;
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	struct nvme_passthru_cmd cmd = { };
+	uint32_t opcode, cdw10, len, i, changed = 0;
+	unsigned char *buf;
+	void *p;
+	int fd, ret;
+
+	if (argc != 5 || parse_u32(argv[2], &opcode) || opcode > 0xff ||
+	    parse_u32(argv[3], &cdw10) || parse_u32(argv[4], &len) || !len) {
+		fprintf(stderr, "usage: %s /dev/nvmeX opcode cdw10 data-len\n",
+			argv[0]);
+		return 2;
+	}
+
+	/*
+	 * Page-align the buffer so that the kernel maps it for the transfer
+	 * instead of bouncing it: a bounce buffer is zero-filled and copied
+	 * back even when the command fails, which would hide the sentinel.
+	 */
+	ret = posix_memalign(&p, 4096, len);
+	if (ret) {
+		fprintf(stderr, "posix_memalign: %s\n", strerror(ret));
+		return 2;
+	}
+	buf = p;
+	memset(buf, SENTINEL, len);
+
+	fd = open(argv[1], O_RDONLY);
+	if (fd < 0) {
+		perror(argv[1]);
+		free(buf);
+		return 2;
+	}
+
+	cmd.opcode = opcode;
+	cmd.addr = (uintptr_t)buf;
+	cmd.data_len = len;
+	cmd.cdw10 = cdw10;
+
+	ret = ioctl(fd, NVME_IOCTL_ADMIN_CMD, &cmd);
+	close(fd);
+	if (ret < 0) {
+		perror("NVME_IOCTL_ADMIN_CMD");
+		free(buf);
+		return 2;
+	}
+
+	for (i = 0; i < len; i++)
+		if (buf[i] != SENTINEL)
+			changed++;
+
+	printf("%#x %u\n", ret, changed);
+	free(buf);
+	return 0;
+}
diff --git a/tests/nvme/071 b/tests/nvme/071
new file mode 100755
index 0000000000000..5333bfac8db53
--- /dev/null
+++ b/tests/nvme/071
@@ -0,0 +1,80 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-3.0+
+# Copyright (C) 2026 Andrea Parri
+#
+# Check that the NVMe target transfers no read data for a failed command.
+# The host buffer is filled with a sentinel, so any data the target sends
+# shows up as changed bytes.
+#
+# Regression test for patch "nvmet-fc: only send read data for successful
+# commands".
+
+. tests/nvme/rc
+
+DESCRIPTION="verify nvmet does not transfer data for failed reads"
+QUICK=1
+
+requires() {
+	_nvme_requires
+	_have_loop
+	_require_kernel_nvme_target
+	_have_src_program nvme-sentinel-read
+}
+
+set_conditions() {
+	_set_nvme_trtype "$@"
+}
+
+# Issue an Identify with CNS $2 to controller $1 and print the NVMe status
+# and the number of changed bytes in the 4096-byte data buffer.
+_identify() {
+	src/nvme-sentinel-read "$1" 0x06 "$2" 4096 2>>"$FULL"
+}
+
+test() {
+	echo "Running ${TEST_NAME}"
+
+	local changed ctrl ns status
+
+	_setup_nvmet
+	# File backing: the namespace read below fails over loop with the
+	# default loop device backing, for reasons unrelated to this test.
+	_nvmet_target_setup --blkdev file
+	_nvme_connect_subsys
+
+	ctrl=$(_find_nvme_dev "$def_subsysnqn")
+	ns="/dev/${ctrl}n1"
+
+	# Identify Controller succeeds and must overwrite the sentinel.
+	if ! read -r status changed < <(_identify "/dev/$ctrl" 0x01); then
+		echo "successful Identify could not be issued"
+	else
+		echo "cns=0x01 status=$status changed=$changed" >>"$FULL"
+		if ((status != 0 || changed == 0)); then
+			echo "successful Identify returned status $status with $changed bytes"
+		fi
+	fi
+
+	# An unsupported CNS fails and must leave the sentinel intact.
+	if ! read -r status changed < <(_identify "/dev/$ctrl" 0xff); then
+		echo "failed Identify could not be issued"
+	else
+		echo "cns=0xff status=$status changed=$changed" >>"$FULL"
+		if (((status & 0x7ff) != 2)); then
+			echo "failed Identify returned status $status, expected 0x2"
+		fi
+		if ((changed != 0)); then
+			echo "failed Identify transferred data: $changed bytes changed"
+		fi
+	fi
+
+	if ! dd if="$ns" of=/dev/null bs=4096 count=256 iflag=direct \
+	     status=none >>"$FULL" 2>&1; then
+		echo "namespace read failed"
+	fi
+
+	_nvme_disconnect_subsys
+	_nvmet_target_cleanup
+
+	echo "Test complete"
+}
diff --git a/tests/nvme/071.out b/tests/nvme/071.out
new file mode 100644
index 0000000000000..146809b91e0a3
--- /dev/null
+++ b/tests/nvme/071.out
@@ -0,0 +1,2 @@
+Running nvme/071
+Test complete
-- 
2.53.0