[PATCH v7 3/3] selftests: statmount: tests for STATMOUNT_BY_FD

29 Nov 2025

Add tests for STATMOUNT_BY_FD flag, which adds support for passing a
file descriptors to statmount(). The fd can also be on a "unmounted"
mount (mount unmounted with MNT_DETACH), we also include tests for that.
Co-developed-by: Andrei Vagin avagin@gmail.com
Signed-off-by: Andrei Vagin avagin@gmail.com
Signed-off-by: Bhavik Sachdev b.sachdev1904@gmail.com
---
 .../filesystems/statmount/statmount.h         |  15 +-
 .../filesystems/statmount/statmount_test.c    | 261 +++++++++++++++++-
 .../filesystems/statmount/statmount_test_ns.c | 101 ++++++-
 3 files changed, 354 insertions(+), 23 deletions(-)

diff --git a/tools/testing/selftests/filesystems/statmount/statmount.h b/tools/testing/selftests/filesystems/statmount/statmount.h
index 99e5ad082fb1..e1cba4bfd8d9 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount.h
+++ b/tools/testing/selftests/filesystems/statmount/statmount.h
@@ -43,19 +43,24 @@
    #endif
 #endif
-static inline int statmount(uint64_t mnt_id, uint64_t mnt_ns_id, uint64_t mask,
-			    struct statmount *buf, size_t bufsize,
+static inline int statmount(uint64_t mnt_id, uint64_t mnt_ns_id, uint32_t fd,
+			    uint64_t mask, struct statmount *buf, size_t bufsize,
    		    unsigned int flags)
 {
    struct mnt_id_req req = {
    	.size = MNT_ID_REQ_SIZE_VER0,
-		.mnt_id = mnt_id,
    	.param = mask,
    };
-	if (mnt_ns_id) {
+	if (flags & STATMOUNT_BY_FD) {
    	req.size = MNT_ID_REQ_SIZE_VER1;
-		req.mnt_ns_id = mnt_ns_id;
+		req.mnt_fd = fd;
+	} else {
+		req.mnt_id = mnt_id;
+		if (mnt_ns_id) {
+			req.size = MNT_ID_REQ_SIZE_VER1;
+			req.mnt_ns_id = mnt_ns_id;
+		}
    }
return syscall(__NR_statmount, &req, buf, bufsize, flags);
diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c
index f048042e53e9..4790a349806e 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount_test.c
+++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c
@@ -33,15 +33,24 @@ static const char *const known_fs[] = {
    "sysv", "tmpfs", "tracefs", "ubifs", "udf", "ufs", "v7", "vboxsf",
    "vfat", "virtiofs", "vxfs", "xenfs", "xfs", "zonefs", NULL };
-static struct statmount *statmount_alloc(uint64_t mnt_id, uint64_t mask, unsigned int flags)
+static struct statmount *statmount_alloc(uint64_t mnt_id, int fd, uint64_t mask, unsigned int flags)
 {
    size_t bufsize = 1 << 15;
-	struct statmount *buf = NULL, *tmp = alloca(bufsize);
+	struct statmount *buf = NULL, *tmp = NULL;
    int tofree = 0;
    int ret;
+	if (flags & STATMOUNT_BY_FD && fd < 0)
+		return NULL;
+
+	tmp = alloca(bufsize);
+
    for (;;) {
-		ret = statmount(mnt_id, 0, mask, tmp, bufsize, flags);
+		if (flags & STATMOUNT_BY_FD)
+			ret = statmount(0, 0, (uint32_t) fd, mask, tmp, bufsize, flags);
+		else
+			ret = statmount(mnt_id, 0, 0, mask, tmp, bufsize, flags);
+
    	if (ret != -1)
    		break;
    	if (tofree)
@@ -237,7 +246,7 @@ static void test_statmount_zero_mask(void)
    struct statmount sm;
    int ret;
-	ret = statmount(root_id, 0, 0, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, 0, 0, &sm, sizeof(sm), 0);
    if (ret == -1) {
    	ksft_test_result_fail("statmount zero mask: %s\n",
    			      strerror(errno));
@@ -263,7 +272,7 @@ static void test_statmount_mnt_basic(void)
    int ret;
    uint64_t mask = STATMOUNT_MNT_BASIC;
-	ret = statmount(root_id, 0, mask, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, 0, mask, &sm, sizeof(sm), 0);
    if (ret == -1) {
    	ksft_test_result_fail("statmount mnt basic: %s\n",
    			      strerror(errno));
@@ -323,7 +332,7 @@ static void test_statmount_sb_basic(void)
    struct statx sx;
    struct statfs sf;
-	ret = statmount(root_id, 0, mask, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, 0, mask, &sm, sizeof(sm), 0);
    if (ret == -1) {
    	ksft_test_result_fail("statmount sb basic: %s\n",
    			      strerror(errno));
@@ -375,7 +384,7 @@ static void test_statmount_mnt_point(void)
 {
    struct statmount *sm;
-	sm = statmount_alloc(root_id, STATMOUNT_MNT_POINT, 0);
+	sm = statmount_alloc(root_id, 0, STATMOUNT_MNT_POINT, 0);
    if (!sm) {
    	ksft_test_result_fail("statmount mount point: %s\n",
    			      strerror(errno));
@@ -405,7 +414,7 @@ static void test_statmount_mnt_root(void)
    assert(last_dir);
    last_dir++;
-	sm = statmount_alloc(root_id, STATMOUNT_MNT_ROOT, 0);
+	sm = statmount_alloc(root_id, 0, STATMOUNT_MNT_ROOT, 0);
    if (!sm) {
    	ksft_test_result_fail("statmount mount root: %s\n",
    			      strerror(errno));
@@ -438,7 +447,7 @@ static void test_statmount_fs_type(void)
    const char *fs_type;
    const char *const *s;
-	sm = statmount_alloc(root_id, STATMOUNT_FS_TYPE, 0);
+	sm = statmount_alloc(root_id, 0, STATMOUNT_FS_TYPE, 0);
    if (!sm) {
    	ksft_test_result_fail("statmount fs type: %s\n",
    			      strerror(errno));
@@ -467,7 +476,7 @@ static void test_statmount_mnt_opts(void)
    char *line = NULL;
    size_t len = 0;
-	sm = statmount_alloc(root_id, STATMOUNT_MNT_BASIC | STATMOUNT_MNT_OPTS,
+	sm = statmount_alloc(root_id, 0, STATMOUNT_MNT_BASIC | STATMOUNT_MNT_OPTS,
    		     0);
    if (!sm) {
    	ksft_test_result_fail("statmount mnt opts: %s\n",
@@ -557,7 +566,7 @@ static void test_statmount_string(uint64_t mask, size_t off, const char *name)
    uint32_t start, i;
    int ret;
-	sm = statmount_alloc(root_id, mask, 0);
+	sm = statmount_alloc(root_id, 0, mask, 0);
    if (!sm) {
    	ksft_test_result_fail("statmount %s: %s\n", name,
    			      strerror(errno));
@@ -586,14 +595,14 @@ static void test_statmount_string(uint64_t mask, size_t off, const char *name)
    exactsize = sm->size;
    shortsize = sizeof(*sm) + i;
-	ret = statmount(root_id, 0, mask, sm, exactsize, 0);
+	ret = statmount(root_id, 0, 0, mask, sm, exactsize, 0);
    if (ret == -1) {
    	ksft_test_result_fail("statmount exact size: %s\n",
    			      strerror(errno));
    	goto out;
    }
    errno = 0;
-	ret = statmount(root_id, 0, mask, sm, shortsize, 0);
+	ret = statmount(root_id, 0, 0, mask, sm, shortsize, 0);
    if (ret != -1 || errno != EOVERFLOW) {
    	ksft_test_result_fail("should have failed with EOVERFLOW: %s\n",
    			      strerror(errno));
@@ -658,6 +667,226 @@ static void test_listmount_tree(void)
    ksft_test_result_pass("listmount tree\n");
 }
+static void test_statmount_by_fd(void)
+{
+	struct statmount *sm = NULL;
+	char tmpdir[] = "/statmount.fd.XXXXXX";
+	const char root[] = "/test";
+	char subdir[PATH_MAX], tmproot[PATH_MAX];
+	int fd;
+
+	if (!mkdtemp(tmpdir)) {
+		ksft_perror("mkdtemp");
+		return;
+	}
+
+	if (mount("statmount.test", tmpdir, "tmpfs", 0, NULL)) {
+		ksft_perror("mount");
+		rmdir(tmpdir);
+		return;
+	}
+
+	snprintf(subdir, PATH_MAX, "%s%s", tmpdir, root);
+	snprintf(tmproot, PATH_MAX, "%s/%s", tmpdir, "chroot");
+
+	if (mkdir(subdir, 0755)) {
+		ksft_perror("mkdir");
+		goto err_tmpdir;
+	}
+
+	if (mount(subdir, subdir, NULL, MS_BIND, 0)) {
+		ksft_perror("mount");
+		goto err_subdir;
+	}
+
+	if (mkdir(tmproot, 0755)) {
+		ksft_perror("mkdir");
+		goto err_subdir;
+	}
+
+	fd = open(subdir, O_PATH);
+	if (fd < 0) {
+		ksft_perror("open");
+		goto err_tmproot;
+	}
+
+	if (chroot(tmproot)) {
+		ksft_perror("chroot");
+		goto err_fd;
+	}
+
+	sm = statmount_alloc(0, fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT, STATMOUNT_BY_FD);
+	if (!sm) {
+		ksft_test_result_fail("statmount by fd failed: %s\n", strerror(errno));
+		goto err_chroot;
+	}
+
+	if (sm->size < sizeof(*sm)) {
+		ksft_test_result_fail("unexpected size: %u < %u\n",
+				      sm->size, (uint32_t) sizeof(*sm));
+		goto err_chroot;
+	}
+
+	if (sm->mask & STATMOUNT_MNT_POINT) {
+		ksft_test_result_fail("STATMOUNT_MNT_POINT unexpectedly set in statmount\n");
+		goto err_chroot;
+	}
+
+	if (!(sm->mask & STATMOUNT_MNT_ROOT)) {
+		ksft_test_result_fail("STATMOUNT_MNT_ROOT not set in statmount\n");
+		goto err_chroot;
+	}
+
+	if (strcmp(root, sm->str + sm->mnt_root) != 0) {
+		ksft_test_result_fail("statmount returned incorrect mnt_root,"
+			"statmount mnt_root: %s != %s\n",
+			sm->str + sm->mnt_root, root);
+		goto err_chroot;
+	}
+
+	if (chroot(".")) {
+		ksft_perror("chroot");
+		goto out;
+	}
+
+	free(sm);
+	sm = statmount_alloc(0, fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT, STATMOUNT_BY_FD);
+	if (!sm) {
+		ksft_test_result_fail("statmount by fd failed: %s\n", strerror(errno));
+		goto err_fd;
+	}
+
+	if (sm->size < sizeof(*sm)) {
+		ksft_test_result_fail("unexpected size: %u < %u\n",
+				      sm->size, (uint32_t) sizeof(*sm));
+		goto out;
+	}
+
+	if (!(sm->mask & STATMOUNT_MNT_POINT)) {
+		ksft_test_result_fail("STATMOUNT_MNT_POINT not set in statmount\n");
+		goto out;
+	}
+
+	if (!(sm->mask & STATMOUNT_MNT_ROOT)) {
+		ksft_test_result_fail("STATMOUNT_MNT_ROOT not set in statmount\n");
+		goto out;
+	}
+
+	if (strcmp(subdir, sm->str + sm->mnt_point) != 0) {
+		ksft_test_result_fail("statmount returned incorrect mnt_point,"
+			"statmount mnt_point: %s != %s\n", sm->str + sm->mnt_point, subdir);
+		goto out;
+	}
+
+	if (strcmp(root, sm->str + sm->mnt_root) != 0) {
+		ksft_test_result_fail("statmount returned incorrect mnt_root,"
+			"statmount mnt_root: %s != %s\n", sm->str + sm->mnt_root, root);
+		goto out;
+	}
+
+	ksft_test_result_pass("statmount by fd\n");
+	goto out;
+err_chroot:
+	chroot(".");
+out:
+	free(sm);
+err_fd:
+	close(fd);
+err_tmproot:
+	rmdir(tmproot);
+err_subdir:
+	umount2(subdir, MNT_DETACH);
+	rmdir(subdir);
+err_tmpdir:
+	umount2(tmpdir, MNT_DETACH);
+	rmdir(tmpdir);
+}
+
+static void test_statmount_by_fd_unmounted(void)
+{
+	const char root[] = "/test.unmounted";
+	char tmpdir[] = "/statmount.fd.XXXXXX";
+	char subdir[PATH_MAX];
+	int fd;
+	struct statmount *sm = NULL;
+
+	if (!mkdtemp(tmpdir)) {
+		ksft_perror("mkdtemp");
+		return;
+	}
+
+	if (mount("statmount.test", tmpdir, "tmpfs", 0, NULL)) {
+		ksft_perror("mount");
+		rmdir(tmpdir);
+		return;
+	}
+
+	snprintf(subdir, PATH_MAX, "%s%s", tmpdir, root);
+
+	if (mkdir(subdir, 0755)) {
+		ksft_perror("mkdir");
+		goto err_tmpdir;
+	}
+
+	if (mount(subdir, subdir, 0, MS_BIND, NULL)) {
+		ksft_perror("mount");
+		goto err_subdir;
+	}
+
+	fd = open(subdir, O_PATH);
+	if (fd < 0) {
+		ksft_perror("open");
+		goto err_subdir;
+	}
+
+	if (umount2(tmpdir, MNT_DETACH)) {
+		ksft_perror("umount2");
+		goto err_fd;
+	}
+
+	sm = statmount_alloc(0, fd, STATMOUNT_MNT_POINT | STATMOUNT_MNT_ROOT, STATMOUNT_BY_FD);
+	if (!sm) {
+		ksft_test_result_fail("statmount by fd unmounted: %s\n",
+				      strerror(errno));
+		goto err_sm;
+	}
+
+	if (sm->size < sizeof(*sm)) {
+		ksft_test_result_fail("unexpected size: %u < %u\n",
+				      sm->size, (uint32_t) sizeof(*sm));
+		goto err_sm;
+	}
+
+	if (sm->mask & STATMOUNT_MNT_POINT) {
+		ksft_test_result_fail("STATMOUNT_MNT_POINT unexpectedly set in mask\n");
+		goto err_sm;
+	}
+
+	if (!(sm->mask & STATMOUNT_MNT_ROOT)) {
+		ksft_test_result_fail("STATMOUNT_MNT_ROOT not set in mask\n");
+		goto err_sm;
+	}
+
+	if (strcmp(sm->str + sm->mnt_root, root) != 0) {
+		ksft_test_result_fail("statmount returned incorrect mnt_root,"
+			"statmount mnt_root: %s != %s\n",
+			sm->str + sm->mnt_root, root);
+		goto err_sm;
+	}
+
+	ksft_test_result_pass("statmount by fd on unmounted mount\n");
+err_sm:
+	free(sm);
+err_fd:
+	close(fd);
+err_subdir:
+	umount2(subdir, MNT_DETACH);
+	rmdir(subdir);
+err_tmpdir:
+	umount2(tmpdir, MNT_DETACH);
+	rmdir(tmpdir);
+}
+
 #define str_off(memb) (offsetof(struct statmount, memb) / sizeof(uint32_t))
int main(void)
@@ -669,14 +898,14 @@ int main(void)
ksft_print_header();
-	ret = statmount(0, 0, 0, NULL, 0, 0);
+	ret = statmount(0, 0, 0, 0, NULL, 0, 0);
    assert(ret == -1);
    if (errno == ENOSYS)
    	ksft_exit_skip("statmount() syscall not supported\n");
setup_namespace();
-	ksft_set_plan(15);
+	ksft_set_plan(17);
    test_listmount_empty_root();
    test_statmount_zero_mask();
    test_statmount_mnt_basic();
@@ -693,6 +922,8 @@ int main(void)
    test_statmount_string(all_mask, str_off(fs_type), "fs type & all");
test_listmount_tree();
+	test_statmount_by_fd_unmounted();
+	test_statmount_by_fd();
if (ksft_get_fail_cnt() + ksft_get_error_cnt() > 0)
diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test_ns.c b/tools/testing/selftests/filesystems/statmount/statmount_test_ns.c
index 605a3fa16bf7..6449b50dde0c 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount_test_ns.c
+++ b/tools/testing/selftests/filesystems/statmount/statmount_test_ns.c
@@ -102,7 +102,7 @@ static int _test_statmount_mnt_ns_id(void)
    if (!root_id)
    	return NSID_ERROR;
-	ret = statmount(root_id, 0, STATMOUNT_MNT_NS_ID, &sm, sizeof(sm), 0);
+	ret = statmount(root_id, 0, 0, STATMOUNT_MNT_NS_ID, &sm, sizeof(sm), 0);
    if (ret == -1) {
    	ksft_print_msg("statmount mnt ns id: %s\n", strerror(errno));
    	return NSID_ERROR;
@@ -128,6 +128,98 @@ static int _test_statmount_mnt_ns_id(void)
    return NSID_PASS;
 }
+static int _test_statmount_mnt_ns_id_by_fd(void)
+{
+	struct statmount sm;
+	uint64_t mnt_ns_id;
+	int ret, fd, mounted = 1, status = NSID_ERROR;
+	char mnt[] = "/statmount.fd.XXXXXX";
+
+	ret = get_mnt_ns_id("/proc/self/ns/mnt", &mnt_ns_id);
+	if (ret != NSID_PASS)
+		return ret;
+
+	if (!mkdtemp(mnt)) {
+		ksft_print_msg("statmount by fd mnt ns id mkdtemp: %s\n", strerror(errno));
+		return NSID_ERROR;
+	}
+
+	if (mount(mnt, mnt, NULL, MS_BIND, 0)) {
+		ksft_print_msg("statmount by fd mnt ns id mount: %s\n", strerror(errno));
+		status = NSID_ERROR;
+		goto err;
+	}
+
+	fd = open(mnt, O_PATH);
+	if (fd < 0) {
+		ksft_print_msg("statmount by fd mnt ns id open: %s\n", strerror(errno));
+		goto err;
+	}
+
+	ret = statmount(0, 0, fd, STATMOUNT_MNT_NS_ID, &sm, sizeof(sm), STATMOUNT_BY_FD);
+	if (ret == -1) {
+		ksft_print_msg("statmount mnt ns id statmount: %s\n", strerror(errno));
+		status = NSID_ERROR;
+		goto out;
+	}
+
+	if (sm.size != sizeof(sm)) {
+		ksft_print_msg("unexpected size: %u != %u\n", sm.size,
+			       (uint32_t)sizeof(sm));
+		status = NSID_FAIL;
+		goto out;
+	}
+	if (sm.mask != STATMOUNT_MNT_NS_ID) {
+		ksft_print_msg("statmount mnt ns id unavailable\n");
+		status = NSID_SKIP;
+		goto out;
+	}
+
+	if (sm.mnt_ns_id != mnt_ns_id) {
+		ksft_print_msg("unexpected mnt ns ID: 0x%llx != 0x%llx\n",
+			       (unsigned long long)sm.mnt_ns_id,
+			       (unsigned long long)mnt_ns_id);
+		status = NSID_FAIL;
+		goto out;
+	}
+
+	mounted = 0;
+	if (umount2(mnt, MNT_DETACH)) {
+		ksft_print_msg("statmount by fd mnt ns id umount2: %s\n", strerror(errno));
+		goto out;
+	}
+
+	ret = statmount(0, 0, fd, STATMOUNT_MNT_NS_ID, &sm, sizeof(sm), STATMOUNT_BY_FD);
+	if (ret == -1) {
+		ksft_print_msg("statmount mnt ns id statmount: %s\n", strerror(errno));
+		status = NSID_ERROR;
+		goto out;
+	}
+
+	if (sm.size != sizeof(sm)) {
+		ksft_print_msg("unexpected size: %u != %u\n", sm.size,
+			       (uint32_t)sizeof(sm));
+		status = NSID_FAIL;
+		goto out;
+	}
+
+	if (sm.mask == STATMOUNT_MNT_NS_ID) {
+		ksft_print_msg("unexpected STATMOUNT_MNT_NS_ID in mask\n");
+		status = NSID_FAIL;
+		goto out;
+	}
+
+	status = NSID_PASS;
+out:
+	close(fd);
+	if (mounted)
+		umount2(mnt, MNT_DETACH);
+err:
+	rmdir(mnt);
+	return status;
+}
+
+
 static void test_statmount_mnt_ns_id(void)
 {
    pid_t pid;
@@ -148,6 +240,9 @@ static void test_statmount_mnt_ns_id(void)
    if (ret != NSID_PASS)
    	exit(ret);
    ret = _test_statmount_mnt_ns_id();
+	if (ret != NSID_PASS)
+		exit(ret);
+	ret = _test_statmount_mnt_ns_id_by_fd();
    exit(ret);
 }
@@ -179,7 +274,7 @@ static int validate_external_listmount(pid_t pid, uint64_t child_nr_mounts)
    for (int i = 0; i < nr_mounts; i++) {
    	struct statmount sm;
-		ret = statmount(list[i], mnt_ns_id, STATMOUNT_MNT_NS_ID, &sm,
+		ret = statmount(list[i], mnt_ns_id, 0, STATMOUNT_MNT_NS_ID, &sm,
    			sizeof(sm), 0);
    	if (ret < 0) {
    		ksft_print_msg("statmount mnt ns id: %s\n", strerror(errno));
@@ -275,7 +370,7 @@ int main(void)
    int ret;
ksft_print_header();
-	ret = statmount(0, 0, 0, NULL, 0, 0);
+	ret = statmount(0, 0, 0, 0, NULL, 0, 0);
    assert(ret == -1);
    if (errno == ENOSYS)
    	ksft_exit_skip("statmount() syscall not supported\n");
-- 
2.52.0



    

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[PATCH v7 3/3] selftests: statmount: tests for STATMOUNT_BY_FD