[LTP] [PATCH v5 1/3] lib: add tst_test.needs_debugfs flag
Piotr Kubaj
piotr.kubaj@intel.com
Wed Oct 21 10:59:30 CEST 2026
Tests reading debugfs files each carry the same statfs() and mount()
dance, because /sys/kernel/debug exists as a plain sysfs directory even
when debugfs is not mounted on it, so checking for the path is not
enough.
With needs_debugfs set the library mounts debugfs during setup, exits
with TCONF if it cannot, and unmounts it at the end only if it did the
mount. The flag implies needs_root. Add TST_DEBUGFS_PATH for tests to
build their paths from, register the flag in the metadata parser and add
a lib/newlib_tests self-test.
Signed-off-by: Piotr Kubaj <piotr.kubaj@intel.com>
---
doc/developers/writing_tests.rst | 3 +++
include/tst_fs.h | 6 +++++
include/tst_test.h | 8 ++++++
lib/newlib_tests/.gitignore | 1 +
lib/newlib_tests/runtest.sh | 1 +
lib/newlib_tests/tst_needs_debugfs.c | 32 +++++++++++++++++++++++
lib/tst_test.c | 38 ++++++++++++++++++++++++++++
metadata/metaparse.c | 1 +
8 files changed, 90 insertions(+)
create mode 100644 lib/newlib_tests/tst_needs_debugfs.c
diff --git a/doc/developers/writing_tests.rst b/doc/developers/writing_tests.rst
index 9a56c0265..5d08cd907 100644
--- a/doc/developers/writing_tests.rst
+++ b/doc/developers/writing_tests.rst
@@ -448,6 +448,9 @@ shell API. For tests using the new shell loader library, see
* - .needs_cpu_vendor
- \-
+ * - .needs_debugfs
+ - \-
+
* - .needs_devfs
- \-
diff --git a/include/tst_fs.h b/include/tst_fs.h
index 80eb1292e..278bbab17 100644
--- a/include/tst_fs.h
+++ b/include/tst_fs.h
@@ -8,6 +8,7 @@
/* man 2 statfs or kernel-source/include/uapi/linux/magic.h */
#define TST_BTRFS_MAGIC 0x9123683E
+#define TST_DEBUGFS_MAGIC 0x64626720
#define TST_NFS_MAGIC 0x6969
#define TST_RAMFS_MAGIC 0x858458f6
#define TST_TMPFS_MAGIC 0x01021994
@@ -58,6 +59,11 @@ enum {
#define OVL_WORK OVL_BASE_MNTPOINT"/work"
#define OVL_MNT OVL_BASE_MNTPOINT"/ovl"
+/**
+ * TST_DEBUGFS_PATH - Where debugfs is mounted by tst_test.needs_debugfs.
+ */
+#define TST_DEBUGFS_PATH "/sys/kernel/debug"
+
/*
* @path: path is the pathname of any file within the mounted file system
* @mult: mult should be TST_KB, TST_MB or TST_GB
diff --git a/include/tst_test.h b/include/tst_test.h
index 80b46f9b1..9e464ea85 100644
--- a/include/tst_test.h
+++ b/include/tst_test.h
@@ -358,6 +358,13 @@ struct tst_fs {
* needed for tests that need to create device files since tmpfs
* at /tmp is usually mounted with 'nodev' option.
*
+ * @needs_debugfs: If set debugfs is mounted at TST_DEBUGFS_PATH i.e.
+ * /sys/kernel/debug, unless it is mounted there already, and
+ * the test exits with TCONF if it cannot be. The library
+ * unmounts it at the end of the test if it mounted it. Both
+ * mounting debugfs and reading its content require root, so
+ * the flag implies tst_test.needs_root.
+ *
* @restore_wallclock: Saves wall clock at the start of the test and restores
* it at the end with the help of monotonic timers.
* Testcases that modify system wallclock use this to
@@ -576,6 +583,7 @@ struct tst_fs {
unsigned int child_needs_reinit:1;
unsigned int runs_script:1;
unsigned int needs_devfs:1;
+ unsigned int needs_debugfs:1;
unsigned int restore_wallclock:1;
unsigned int all_filesystems:1;
diff --git a/lib/newlib_tests/.gitignore b/lib/newlib_tests/.gitignore
index 3a6e1643c..24008fa5c 100644
--- a/lib/newlib_tests/.gitignore
+++ b/lib/newlib_tests/.gitignore
@@ -59,6 +59,7 @@ tst_needs_cmds05
tst_needs_cmds06
tst_needs_cmds07
tst_needs_cmds08
+tst_needs_debugfs
test_runtime01
test_runtime02
test_children_cleanup
diff --git a/lib/newlib_tests/runtest.sh b/lib/newlib_tests/runtest.sh
index 71808ef8b..1a51d8b7a 100755
--- a/lib/newlib_tests/runtest.sh
+++ b/lib/newlib_tests/runtest.sh
@@ -27,6 +27,7 @@ tst_expiration_timer
tst_filesystems01
tst_fuzzy_sync0[1-3]
tst_needs_cmds0[1-36-8]
+tst_needs_debugfs
tst_res_hexd
tst_safe_sscanf
tst_strstatus}"
diff --git a/lib/newlib_tests/tst_needs_debugfs.c b/lib/newlib_tests/tst_needs_debugfs.c
new file mode 100644
index 000000000..7689665a4
--- /dev/null
+++ b/lib/newlib_tests/tst_needs_debugfs.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2026 Piotr Kubaj <piotr.kubaj@intel.com>
+ */
+
+/*
+ * Test that tst_test.needs_debugfs gets debugfs mounted for the test.
+ *
+ * Run it both with debugfs mounted and with it unmounted, it has to pass either
+ * way. In the latter case the library reports mounting debugfs and has to leave
+ * it unmounted once the test is over.
+ */
+
+#include <sys/vfs.h>
+#include "tst_test.h"
+
+static void run(void)
+{
+ struct statfs sfs;
+
+ SAFE_STATFS(TST_DEBUGFS_PATH, &sfs);
+
+ if (sfs.f_type == TST_DEBUGFS_MAGIC)
+ tst_res(TPASS, "debugfs is mounted at %s", TST_DEBUGFS_PATH);
+ else
+ tst_res(TFAIL, "debugfs is not mounted at %s", TST_DEBUGFS_PATH);
+}
+
+static struct tst_test test = {
+ .needs_debugfs = 1,
+ .test_all = run,
+};
diff --git a/lib/tst_test.c b/lib/tst_test.c
index 10ff73397..a42d3f462 100644
--- a/lib/tst_test.c
+++ b/lib/tst_test.c
@@ -15,6 +15,7 @@
#include <errno.h>
#include <sys/mount.h>
#include <sys/types.h>
+#include <sys/vfs.h>
#include <sys/utsname.h>
#include <sys/wait.h>
#include <math.h>
@@ -81,6 +82,7 @@ struct context {
tst_atomic_t abort_flag;
uint32_t mntpoint_mounted:1;
uint32_t ovl_mounted:1;
+ uint32_t debugfs_mounted:1;
uint32_t tdebug;
};
@@ -1224,6 +1226,31 @@ static void prepare_and_mount_dev_fs(const char *mntpoint)
}
}
+static void mount_debugfs(void)
+{
+ struct statfs sfs;
+
+ /*
+ * TST_DEBUGFS_PATH exists as a plain sysfs directory whenever
+ * CONFIG_DEBUG_FS is enabled, whether or not debugfs is mounted on it,
+ * so the filesystem type has to be checked rather than the directory
+ * being present.
+ */
+ if (statfs(TST_DEBUGFS_PATH, &sfs))
+ tst_brk(TCONF | TERRNO, "Can't statfs %s", TST_DEBUGFS_PATH);
+
+ if (sfs.f_type == TST_DEBUGFS_MAGIC)
+ return;
+
+ if (mount("debugfs", TST_DEBUGFS_PATH, "debugfs", 0, NULL)) {
+ tst_brk(TCONF | TERRNO, "Can't mount debugfs at %s",
+ TST_DEBUGFS_PATH);
+ }
+
+ tst_res(TINFO, "Mounted debugfs at %s", TST_DEBUGFS_PATH);
+ context->debugfs_mounted = 1;
+}
+
static void prepare_and_mount_hugetlb_fs(void)
{
if (access(PATH_MM_HUGEPAGES, F_OK))
@@ -1474,6 +1501,9 @@ static void do_setup(int argc, char *argv[])
if (tst_test->needs_kconfigs && tst_kconfig_check(tst_test->needs_kconfigs))
tst_brk(TCONF, "Aborting due to unsuitable kernel config, see above!");
+ if (tst_test->needs_debugfs)
+ tst_test->needs_root = 1;
+
if (tst_test->needs_root && geteuid() != 0)
tst_brk(TCONF, "Test needs to be run as root");
@@ -1565,6 +1595,9 @@ static void do_setup(int argc, char *argv[])
"Two or more of needs_{rofs, devfs, device, hugetlbfs} are set");
}
+ if (tst_test->needs_debugfs)
+ mount_debugfs();
+
if (tst_test->needs_devfs)
prepare_and_mount_dev_fs(tst_test->mntpoint);
@@ -1676,6 +1709,11 @@ static void do_cleanup(void)
if (context->mntpoint_mounted)
tst_umount(tst_test->mntpoint);
+ if (context->debugfs_mounted) {
+ tst_umount(TST_DEBUGFS_PATH);
+ context->debugfs_mounted = 0;
+ }
+
if (tst_test->needs_device && tdev.dev)
tst_release_device(tdev.dev);
diff --git a/metadata/metaparse.c b/metadata/metaparse.c
index cb141c383..7f2c09037 100644
--- a/metadata/metaparse.c
+++ b/metadata/metaparse.c
@@ -1169,6 +1169,7 @@ static struct typemap tst_test_typemap[] = {
{.id = "child_needs_reinit", .type = DATA_BOOL},
{.id = "runs_script", .type = DATA_BOOL},
{.id = "needs_devfs", .type = DATA_BOOL},
+ {.id = "needs_debugfs", .type = DATA_BOOL},
{.id = "restore_wallclock", .type = DATA_BOOL},
{.id = "all_filesystems", .type = DATA_BOOL},
{.id = "skip_in_lockdown", .type = DATA_BOOL},
--
2.47.3
---------------------------------------------------------------------
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