[LTP] [PATCH v4] move_mount03: check allow to mount beneath top mount

[Wei Gao]

Signed-off-by: Wei Gao <wegao@suse.com>
---
 include/lapi/fsmount.h                        |   4 +
 runtest/syscalls                              |   1 +
 .../kernel/syscalls/move_mount/.gitignore     |   1 +
 .../kernel/syscalls/move_mount/move_mount03.c | 137 ++++++++++++++++++
 4 files changed, 143 insertions(+)
 create mode 100644 testcases/kernel/syscalls/move_mount/move_mount03.c

diff --git a/include/lapi/fsmount.h b/include/lapi/fsmount.h
index 07eb42ffa..216e966c7 100644
--- a/include/lapi/fsmount.h
+++ b/include/lapi/fsmount.h
@@ -115,6 +115,10 @@ static inline int mount_setattr(int dirfd, const char *from_pathname, unsigned i
 }
 #endif /* HAVE_MOUNT_SETATTR */
 
+#ifndef MOVE_MOUNT_BENEATH
+#define MOVE_MOUNT_BENEATH 		0x00000200
+#endif /* MOVE_MOUNT_BENEATH */
+
 /*
  * New headers added in kernel after 5.2 release, create them for old userspace.
 */
diff --git a/runtest/syscalls b/runtest/syscalls
index b1125dd75..04b758fd9 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -824,6 +824,7 @@ mount_setattr01 mount_setattr01
 
 move_mount01 move_mount01
 move_mount02 move_mount02
+move_mount03 move_mount03
 
 move_pages01 move_pages01
 move_pages02 move_pages02
diff --git a/testcases/kernel/syscalls/move_mount/.gitignore b/testcases/kernel/syscalls/move_mount/.gitignore
index 83ae40145..ddfe10128 100644
--- a/testcases/kernel/syscalls/move_mount/.gitignore
+++ b/testcases/kernel/syscalls/move_mount/.gitignore
@@ -1,2 +1,3 @@
 /move_mount01
 /move_mount02
+/move_mount03
diff --git a/testcases/kernel/syscalls/move_mount/move_mount03.c b/testcases/kernel/syscalls/move_mount/move_mount03.c
new file mode 100644
index 000000000..dfdad080e
--- /dev/null
+++ b/testcases/kernel/syscalls/move_mount/move_mount03.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2023 Christian Brauner <brauner@kernel.org>
+ * Copyright (c) 2023 Wei Gao <wegao@suse.com>
+ */
+
+/*\
+ * [Description]
+ *
+ * Test allow to mount beneath top mount feature
+ */
+
+/*
+ * Test create for following commit:
+ * commit 6ac392815628f317fcfdca1a39df00b9cc4ebc8b
+ * Author: Christian Brauner <brauner@kernel.org>
+ * Date:   Wed May 3 13:18:42 2023 +0200
+ *     fs: allow to mount beneath top mount
+ *
+ * Above commit has heavily commented but i found following commit
+ * contain simple summary of this feature for easy understanding:
+ *
+ * commit c0a572d9d32fe1e95672f24e860776dba0750a38
+ * Author: Linus Torvalds <torvalds@linux-foundation.org>
+ *       TL;DR:
+ *
+ *         > mount -t ext4 /dev/sda /mnt
+ *           |
+ *           --/mnt    /dev/sda    ext4
+ *
+ *         > mount --beneath -t xfs /dev/sdb /mnt
+ *           |
+ *           --/mnt    /dev/sdb    xfs
+ *             --/mnt  /dev/sda    ext4
+ *
+ *         > umount /mnt
+ *           |
+ *           --/mnt    /dev/sdb    xfs
+ *
+ * So base above scenario design following scenario for LTP check:
+ *
+ *         > mount -t tmpfs /DIRA
+ *           |
+ *           --/DIRA(create A file within DIRA)
+ *
+ *         > mount -t tmpfs /DIRB
+ *           |
+ *           --/DIRA(create B file within DIRB)
+ *
+ *         > move_mount --beneath /DIRA /DIRB
+ *           |
+ *           --/mnt    /DIRA /DIRB
+ *             --/mnt  /DIRB
+ *
+ *         If you check content of /DIRB, you can see file B
+ *
+ *         > umount /DIRB
+ *           |
+ *           --/mnt    /DIRA /DIRB
+ *         Check content of /DIRB, you can see file A exist since
+ *         current /DIRB mount source is already become /DIRA
+ *
+ * See also:
+ * https://lwn.net/Articles/930591/
+ * https://github.com/brauner/move-mount-beneath
+ */
+
+#include <stdio.h>
+
+#include "tst_test.h"
+#include "lapi/fsmount.h"
+#include "lapi/sched.h"
+
+#define DIRA "LTP_DIR_A"
+#define DIRB "LTP_DIR_B"
+
+static int fda = -1, fdb = -1;
+
+static void run(void)
+{
+	SAFE_MOUNT("none", DIRA, "tmpfs", 0, 0);
+	SAFE_MOUNT("none", DIRB, "tmpfs", 0, 0);
+	SAFE_TOUCH(DIRA "/A", 0, NULL);
+	SAFE_TOUCH(DIRB "/B", 0, NULL);
+
+	fda = open_tree(AT_FDCWD, DIRA, OPEN_TREE_CLOEXEC | OPEN_TREE_CLONE);
+	if (fda == -1)
+		tst_brk(TBROK | TERRNO, "open_tree() failed");
+
+	fdb = SAFE_OPEN(DIRB, O_PATH | O_NOFOLLOW, 0666);
+	TST_EXP_PASS(move_mount(fda, "", fdb, "",
+				MOVE_MOUNT_BENEATH | MOVE_MOUNT_F_EMPTY_PATH |
+				MOVE_MOUNT_T_EMPTY_PATH));
+	SAFE_CLOSE(fda);
+	SAFE_CLOSE(fdb);
+
+	TST_EXP_PASS(access(DIRB "/B", F_OK));
+	SAFE_UMOUNT(DIRB);
+	TST_EXP_PASS(access(DIRB "/A", F_OK));
+
+	SAFE_UMOUNT(DIRB);
+	SAFE_UMOUNT(DIRA);
+}
+
+static void setup(void)
+{
+	SAFE_MKDIR(DIRA, 0777);
+	SAFE_MKDIR(DIRB, 0777);
+}
+
+static void cleanup(void)
+{
+
+	if (fda >= 0)
+		SAFE_CLOSE(fda);
+
+	if (fdb >= 0)
+		SAFE_CLOSE(fdb);
+
+	if (tst_is_mounted_at_tmpdir(DIRA))
+		SAFE_UMOUNT(DIRA);
+
+	if (tst_is_mounted_at_tmpdir(DIRB))
+		SAFE_UMOUNT(DIRB);
+
+	if (tst_is_mounted_at_tmpdir(DIRB))
+		SAFE_UMOUNT(DIRB);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.needs_root = 1,
+	.min_kver = "6.5.0",
+	.needs_tmpdir = 1,
+	.setup = setup,
+	.cleanup = cleanup,
+};
-- 
2.35.3