selftests/statmount: add statmount_alloc() helper

Add a helper to allocate a statmount buffer and call statmount(). This
helper will be shared by multiple test suites that need to query mount
information via statmount().

Link: https://patch.msgid.link/20260122-work-fsmount-namespace-v1-5-5ef0a886e646@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

3 files changed, 58 insertions, 46 deletions

diff --git a/tools/testing/selftests/filesystems/open_tree_ns/open_tree_ns_test.c b/tools/testing/selftests/filesystems/open_tree_ns/open_tree_ns_test.c
index 9711556280ae..86d5d7a831c1 100644
--- a/tools/testing/selftests/filesystems/open_tree_ns/open_tree_ns_test.c
+++ b/tools/testing/selftests/filesystems/open_tree_ns/open_tree_ns_test.c
@@ -115,7 +115,7 @@ static void dump_mounts(struct __test_metadata *_metadata, uint64_t mnt_ns_id)
 				     STATMOUNT_MNT_BASIC |
 				     STATMOUNT_FS_TYPE |
 				     STATMOUNT_MNT_ROOT |
-				     STATMOUNT_MNT_POINT);
+				     STATMOUNT_MNT_POINT, 0);
 		if (!sm) {
 			TH_LOG("  [%zd] mnt_id %llu: statmount failed: %s",
 			       i, (unsigned long long)list[i], strerror(errno));
@@ -746,7 +746,7 @@ TEST_F(open_tree_ns_userns, umount_fails_einval)
 			const char *mnt_point;
 
 			sm = statmount_alloc(list[i], new_ns_id,
-					     STATMOUNT_MNT_POINT);
+					     STATMOUNT_MNT_POINT, 0);
 			if (!sm)
 				_exit(11);
 
@@ -863,7 +863,7 @@ TEST_F(open_tree_ns_userns, umount_succeeds)
 			const char *mnt_point;
 
 			sm = statmount_alloc(list[i], new_ns_id,
-					     STATMOUNT_MNT_POINT);
+					     STATMOUNT_MNT_POINT, 0);
 			if (!sm)
 				_exit(11);
 
@@ -1003,7 +1003,7 @@ TEST_F(open_tree_ns_unbindable, recursive_skips_on_unbindable)
 		struct statmount *sm;
 		const char *mnt_point;
 
-		sm = statmount_alloc(list[i], new_ns_id, STATMOUNT_MNT_POINT);
+		sm = statmount_alloc(list[i], new_ns_id, STATMOUNT_MNT_POINT, 0);
 		ASSERT_NE(sm, NULL) {
 			TH_LOG("statmount_alloc failed for mnt_id %llu",
 			       (unsigned long long)list[i]);
diff --git a/tools/testing/selftests/filesystems/statmount/statmount.h b/tools/testing/selftests/filesystems/statmount/statmount.h
index e1cba4bfd8d9..675f7cc00076 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount.h
+++ b/tools/testing/selftests/filesystems/statmount/statmount.h
@@ -3,10 +3,14 @@
 #ifndef __STATMOUNT_H
 #define __STATMOUNT_H
 
+#include <errno.h>
 #include <stdint.h>
+#include <stdlib.h>
 #include <linux/mount.h>
 #include <asm/unistd.h>
 
+#define STATMOUNT_BUFSIZE (1 << 15)
+
 #ifndef __NR_statmount
 	#if defined __alpha__
 		#define __NR_statmount 567
@@ -84,4 +88,51 @@ static inline ssize_t listmount(uint64_t mnt_id, uint64_t mnt_ns_id,
 	return syscall(__NR_listmount, &req, list, num, flags);
 }
 
+static inline struct statmount *statmount_alloc(uint64_t mnt_id, uint64_t mnt_ns_id,
+						 uint64_t mask, unsigned int flags)
+{
+	struct statmount *buf;
+	size_t bufsize = STATMOUNT_BUFSIZE;
+	int ret;
+
+	for (;;) {
+		buf = malloc(bufsize);
+		if (!buf)
+			return NULL;
+
+		ret = statmount(mnt_id, mnt_ns_id, 0, mask, buf, bufsize, flags);
+		if (ret == 0)
+			return buf;
+
+		free(buf);
+		if (errno != EOVERFLOW)
+			return NULL;
+
+		bufsize <<= 1;
+	}
+}
+
+static inline struct statmount *statmount_alloc_by_fd(int fd, uint64_t mask)
+{
+	struct statmount *buf;
+	size_t bufsize = STATMOUNT_BUFSIZE;
+	int ret;
+
+	for (;;) {
+		buf = malloc(bufsize);
+		if (!buf)
+			return NULL;
+
+		ret = statmount(0, 0, fd, mask, buf, bufsize, STATMOUNT_BY_FD);
+		if (ret == 0)
+			return buf;
+
+		free(buf);
+		if (errno != EOVERFLOW)
+			return NULL;
+
+		bufsize <<= 1;
+	}
+}
+
 #endif /* __STATMOUNT_H */
diff --git a/tools/testing/selftests/filesystems/statmount/statmount_test.c b/tools/testing/selftests/filesystems/statmount/statmount_test.c
index a04bcaace126..8dc018d47a93 100644
--- a/tools/testing/selftests/filesystems/statmount/statmount_test.c
+++ b/tools/testing/selftests/filesystems/statmount/statmount_test.c
@@ -33,45 +33,6 @@ 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, int fd, uint64_t mask, unsigned int flags)
-{
-	size_t bufsize = 1 << 15;
-	struct statmount *buf = NULL, *tmp = NULL;
-	int tofree = 0;
-	int ret;
-
-	if (flags & STATMOUNT_BY_FD && fd < 0)
-		return NULL;
-
-	tmp = alloca(bufsize);
-
-	for (;;) {
-		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)
-			free(tmp);
-		if (errno != EOVERFLOW)
-			return NULL;
-		bufsize <<= 1;
-		tofree = 1;
-		tmp = malloc(bufsize);
-		if (!tmp)
-			return NULL;
-	}
-	buf = malloc(tmp->size);
-	if (buf)
-		memcpy(buf, tmp, tmp->size);
-	if (tofree)
-		free(tmp);
-
-	return buf;
-}
-
 static void write_file(const char *path, const char *val)
 {
 	int fd = open(path, O_WRONLY);
@@ -715,7 +676,7 @@ static void test_statmount_by_fd(void)
 		goto err_fd;
 	}
 
-	sm = statmount_alloc(0, fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT, STATMOUNT_BY_FD);
+	sm = statmount_alloc_by_fd(fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT);
 	if (!sm) {
 		ksft_test_result_fail("statmount by fd failed: %s\n", strerror(errno));
 		goto err_chroot;
@@ -750,7 +711,7 @@ static void test_statmount_by_fd(void)
 	}
 
 	free(sm);
-	sm = statmount_alloc(0, fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT, STATMOUNT_BY_FD);
+	sm = statmount_alloc_by_fd(fd, STATMOUNT_MNT_ROOT | STATMOUNT_MNT_POINT);
 	if (!sm) {
 		ksft_test_result_fail("statmount by fd failed: %s\n", strerror(errno));
 		goto err_fd;
@@ -844,7 +805,7 @@ static void test_statmount_by_fd_unmounted(void)
 		goto err_fd;
 	}
 
-	sm = statmount_alloc(0, fd, STATMOUNT_MNT_POINT | STATMOUNT_MNT_ROOT, STATMOUNT_BY_FD);
+	sm = statmount_alloc_by_fd(fd, STATMOUNT_MNT_POINT | STATMOUNT_MNT_ROOT);
 	if (!sm) {
 		ksft_test_result_fail("statmount by fd unmounted: %s\n",
 				      strerror(errno));