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selftests: add test for detached mount tree propagation

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Test that detached mount trees receive propagation events.

Link: https://lore.kernel.org/r/20250225-work-mount-propagation-v1-2-e6e3724500eb@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-02-25 11:15:47 +01:00
parent 064fe6e233
commit 12e40cbb0e
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1 changed files with 70 additions and 0 deletions
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70
tools/testing/selftests/mount_setattr/mount_setattr_test.c
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@ -2097,4 +2097,74 @@ TEST_F(mount_setattr, two_detached_subtrees_of_same_anonymous_mount_namespace)
ASSERT_EQ(move_mount(fd_tree1, "", -EBADF, "/tmp/target1", MOVE_MOUNT_F_EMPTY_PATH), 0);
}
TEST_F(mount_setattr, detached_tree_propagation)
{
int fd_tree = -EBADF;
struct statx stx1, stx2, stx3, stx4;
ASSERT_EQ(unshare(CLONE_NEWNS), 0);
ASSERT_EQ(mount(NULL, "/mnt", NULL, MS_REC | MS_SHARED, NULL), 0);
/*
* Copy the following mount tree:
*
* /mnt testing tmpfs
* |-/mnt/A testing tmpfs
* | `-/mnt/A/AA testing tmpfs
* | `-/mnt/A/AA/B testing tmpfs
* | `-/mnt/A/AA/B/BB testing tmpfs
* `-/mnt/B testing ramfs
*/
fd_tree = sys_open_tree(-EBADF, "/mnt",
AT_NO_AUTOMOUNT | AT_SYMLINK_NOFOLLOW |
AT_RECURSIVE | OPEN_TREE_CLOEXEC |
OPEN_TREE_CLONE);
ASSERT_GE(fd_tree, 0);
ASSERT_EQ(statx(-EBADF, "/mnt/A", 0, 0, &stx1), 0);
ASSERT_EQ(statx(fd_tree, "A", 0, 0, &stx2), 0);
/*
* Copying the mount namespace like done above doesn't alter the
* mounts in any way so the filesystem mounted on /mnt must be
* identical even though the mounts will differ. Use the device
* information to verify that. Note that tmpfs will have a 0
* major number so comparing the major number is misleading.
*/
ASSERT_EQ(stx1.stx_dev_minor, stx2.stx_dev_minor);
/* Mount a tmpfs filesystem over /mnt/A. */
ASSERT_EQ(mount(NULL, "/mnt/A", "tmpfs", 0, NULL), 0);
ASSERT_EQ(statx(-EBADF, "/mnt/A", 0, 0, &stx3), 0);
ASSERT_EQ(statx(fd_tree, "A", 0, 0, &stx4), 0);
/*
* A new filesystem has been mounted on top of /mnt/A which
* means that the device information will be different for any
* statx() that was taken from /mnt/A before the mount compared
* to one after the mount.
*
* Since we already now that the device information between the
* stx1 and stx2 samples are identical we also now that stx2 and
* stx3 device information will necessarily differ.
*/
ASSERT_NE(stx1.stx_dev_minor, stx3.stx_dev_minor);
/*
* If mount propagation worked correctly then the tmpfs mount
* that was created after the mount namespace was unshared will
* have propagated onto /mnt/A in the detached mount tree.
*
* Verify that the device information for stx3 and stx4 are
* identical. It is already established that stx3 is different
* from both stx1 and stx2 sampled before the tmpfs mount was
* done so if stx3 and stx4 are identical the proof is done.
*/
ASSERT_EQ(stx3.stx_dev_minor, stx4.stx_dev_minor);
EXPECT_EQ(close(fd_tree), 0);
}
TEST_HARNESS_MAIN