[RFC PATCH v2 09/14] selftests/kcov_dataflow: add ioctl interface selftest

From: Yunseong Kim

Date: Thu Jun 11 2026 - 12:27:15 EST

Add kselftest_harness-based test in user_ioctl/ covering the
kcov_dataflow ioctl interface (9 TAP cases): init, mmap, enable,
disable, error paths, double-enable rejection, and record capture.

Test:

make -C tools/testing/selftests/kcov_dataflow
./user_ioctl/user_ioctl

Result:

TAP version 13
1..9
# Starting 9 tests from 1 test cases.
# RUN kcov_dataflow.init_track ...
# OK kcov_dataflow.init_track
ok 1 kcov_dataflow.init_track
# RUN kcov_dataflow.init_track_too_small ...
# OK kcov_dataflow.init_track_too_small
ok 2 kcov_dataflow.init_track_too_small
# RUN kcov_dataflow.init_track_double ...
# OK kcov_dataflow.init_track_double
ok 3 kcov_dataflow.init_track_double
# RUN kcov_dataflow.mmap_before_init ...
# OK kcov_dataflow.mmap_before_init
ok 4 kcov_dataflow.mmap_before_init
# RUN kcov_dataflow.enable_disable ...
# OK kcov_dataflow.enable_disable
ok 5 kcov_dataflow.enable_disable
# RUN kcov_dataflow.enable_without_mmap ...
# OK kcov_dataflow.enable_without_mmap
ok 6 kcov_dataflow.enable_without_mmap
# RUN kcov_dataflow.disable_without_enable ...
# OK kcov_dataflow.disable_without_enable
ok 7 kcov_dataflow.disable_without_enable
# RUN kcov_dataflow.double_enable ...
# OK kcov_dataflow.double_enable
ok 8 kcov_dataflow.double_enable
# RUN kcov_dataflow.records_captured ...
# OK kcov_dataflow.records_captured

Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Assisted-by: Claude:claude-opus-4-6 [kiro-chat]
Link: https://github.com/yskzalloc/kcov-dataflow/actions
Signed-off-by: Yunseong Kim <yunseong.kim@xxxxxxxx>
---
tools/testing/selftests/kcov_dataflow/.gitignore | 8 ++
tools/testing/selftests/kcov_dataflow/Makefile | 3 +
tools/testing/selftests/kcov_dataflow/README.rst | 37 +++++
.../kcov_dataflow/user_ioctl/user_ioctl.c | 156 +++++++++++++++++++++
4 files changed, 204 insertions(+)

diff --git a/tools/testing/selftests/kcov_dataflow/.gitignore b/tools/testing/selftests/kcov_dataflow/.gitignore
new file mode 100644
index 000000000000..f71fc89580f8
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/.gitignore
@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: GPL-2.0
+user_ioctl/user_ioctl
+*.o
+*.ko
+*.mod
+*.mod.c
+Module.symvers
+modules.order
diff --git a/tools/testing/selftests/kcov_dataflow/Makefile b/tools/testing/selftests/kcov_dataflow/Makefile
new file mode 100644
index 000000000000..b9fc1c5f0104
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+TEST_GEN_PROGS := user_ioctl/user_ioctl
+include ../lib.mk
diff --git a/tools/testing/selftests/kcov_dataflow/README.rst b/tools/testing/selftests/kcov_dataflow/README.rst
new file mode 100644
index 000000000000..8b650a62acb1
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/README.rst
@@ -0,0 +1,37 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+KCOV-Dataflow Selftests
+========================
+
+This directory contains selftests for the KCOV-Dataflow subsystem
+(``/sys/kernel/debug/kcov_dataflow``).
+
+Prerequisites
+-------------
+
+Build the kernel with::
+
+ CONFIG_KCOV=y
+ CONFIG_KCOV_DATAFLOW_ARGS=y
+ CONFIG_KCOV_DATAFLOW_RET=y
+ CONFIG_DEBUG_INFO=y
+
+For full capture, also enable::
+
+ CONFIG_KCOV_DATAFLOW_INSTRUMENT_ALL=y
+
+Tests
+-----
+
+user_ioctl/user_ioctl.c
+ Automated ioctl interface test (9 TAP cases)::
+
+ make -C tools/testing/selftests/kcov_dataflow
+ ./user_ioctl/user_ioctl
+
+trigger-view.py
+ Loads a test module via finit_module() with recording active,
+ prints captured records with symbol resolution::
+
+ python3 trigger-view.py <module_name>
+ python3 trigger-view.py <module_name> --raw
diff --git a/tools/testing/selftests/kcov_dataflow/user_ioctl/user_ioctl.c b/tools/testing/selftests/kcov_dataflow/user_ioctl/user_ioctl.c
new file mode 100644
index 000000000000..48448bc02d2f
--- /dev/null
+++ b/tools/testing/selftests/kcov_dataflow/user_ioctl/user_ioctl.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * kcov_dataflow_test.c - Selftest for /sys/kernel/debug/kcov_dataflow
+ *
+ * Verifies the ioctl interface: open, INIT_TRACK, mmap, ENABLE, DISABLE.
+ * With INSTRUMENT_ALL, also verifies that records are produced for
+ * syscalls executed while recording is active.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <stdint.h>
+#include <string.h>
+#include <errno.h>
+
+#include "../../kselftest_harness.h"
+
+#define KCOV_DF_INIT_TRACK _IOR('d', 1, unsigned long)
+#define KCOV_DF_ENABLE _IO('d', 100)
+#define KCOV_DF_DISABLE _IO('d', 101)
+
+#define BUF_SIZE 65536
+
+#define DF_TYPE_ENTRY 0xE
+#define DF_TYPE_RET 0xF
+
+FIXTURE(kcov_dataflow) {
+ int fd;
+ uint64_t *buf;
+};
+
+FIXTURE_SETUP(kcov_dataflow)
+{
+ self->fd = open("/sys/kernel/debug/kcov_dataflow", O_RDWR);
+ if (self->fd < 0)
+ SKIP(return, "kcov_dataflow not available (need CONFIG_KCOV_DATAFLOW_ARGS)");
+ self->buf = MAP_FAILED;
+}
+
+FIXTURE_TEARDOWN(kcov_dataflow)
+{
+ if (self->buf != MAP_FAILED)
+ munmap(self->buf, BUF_SIZE * sizeof(uint64_t));
+ if (self->fd >= 0)
+ close(self->fd);
+}
+
+TEST_F(kcov_dataflow, init_track)
+{
+ int ret = ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE);
+
+ ASSERT_EQ(0, ret);
+}
+
+TEST_F(kcov_dataflow, init_track_too_small)
+{
+ int ret = ioctl(self->fd, KCOV_DF_INIT_TRACK, 1UL);
+
+ ASSERT_EQ(-1, ret);
+ ASSERT_EQ(EINVAL, errno);
+}
+
+TEST_F(kcov_dataflow, init_track_double)
+{
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ ASSERT_EQ(-1, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ ASSERT_EQ(EBUSY, errno);
+}
+
+TEST_F(kcov_dataflow, mmap_before_init)
+{
+ self->buf = mmap(NULL, BUF_SIZE * sizeof(uint64_t),
+ PROT_READ | PROT_WRITE, MAP_SHARED, self->fd, 0);
+ ASSERT_EQ(MAP_FAILED, self->buf);
+}
+
+TEST_F(kcov_dataflow, enable_disable)
+{
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ self->buf = mmap(NULL, BUF_SIZE * sizeof(uint64_t),
+ PROT_READ | PROT_WRITE, MAP_SHARED, self->fd, 0);
+ ASSERT_NE(MAP_FAILED, self->buf);
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_ENABLE, 0));
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_DISABLE, 0));
+}
+
+TEST_F(kcov_dataflow, enable_without_mmap)
+{
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ /* enable works even without mmap (mmap is optional for setup) */
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_ENABLE, 0));
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_DISABLE, 0));
+}
+
+TEST_F(kcov_dataflow, disable_without_enable)
+{
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ ASSERT_EQ(-1, ioctl(self->fd, KCOV_DF_DISABLE, 0));
+ ASSERT_EQ(EINVAL, errno);
+}
+
+TEST_F(kcov_dataflow, double_enable)
+{
+ int fd2;
+
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ self->buf = mmap(NULL, BUF_SIZE * sizeof(uint64_t),
+ PROT_READ | PROT_WRITE, MAP_SHARED, self->fd, 0);
+ ASSERT_NE(MAP_FAILED, self->buf);
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_ENABLE, 0));
+
+ /* Second fd should fail to enable (task already active) */
+ fd2 = open("/sys/kernel/debug/kcov_dataflow", O_RDWR);
+ ASSERT_GE(fd2, 0);
+ ASSERT_EQ(0, ioctl(fd2, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ ASSERT_EQ(-1, ioctl(fd2, KCOV_DF_ENABLE, 0));
+ ASSERT_EQ(EBUSY, errno);
+ close(fd2);
+
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_DISABLE, 0));
+}
+
+TEST_F(kcov_dataflow, records_captured)
+{
+ uint64_t count;
+
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_INIT_TRACK, (unsigned long)BUF_SIZE));
+ self->buf = mmap(NULL, BUF_SIZE * sizeof(uint64_t),
+ PROT_READ | PROT_WRITE, MAP_SHARED, self->fd, 0);
+ ASSERT_NE(MAP_FAILED, self->buf);
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_ENABLE, 0));
+
+ /* Trigger some kernel code in this task */
+ getpid();
+
+ ASSERT_EQ(0, ioctl(self->fd, KCOV_DF_DISABLE, 0));
+
+ count = self->buf[0];
+ /*
+ * With INSTRUMENT_ALL, getpid() produces records.
+ * Without it, count may be 0 (no instrumented code).
+ * Either way, the interface works correctly.
+ */
+ if (count > 0) {
+ uint64_t hdr = self->buf[1];
+ unsigned int type = (hdr >> 28) & 0xF;
+
+ /* First record should be ENTRY or RET */
+ ASSERT_TRUE(type == DF_TYPE_ENTRY || type == DF_TYPE_RET);
+ }
+}
+
+TEST_HARNESS_MAIN

--
2.43.0