Add a test suite for the UNSHARE_EMPTY_MNTNS and CLONE_EMPTY_MNTNS
flags exercising the empty mount namespace functionality through the
kselftest harness.
The tests cover:
- basic functionality: unshare succeeds, exactly one mount exists in
the new namespace, root and cwd point to the same mount
- flag interactions: UNSHARE_EMPTY_MNTNS works standalone without
explicit CLONE_NEWNS, combines correctly with CLONE_NEWUSER and
other namespace flags (CLONE_NEWUTS, CLONE_NEWIPC)
- edge cases: EPERM without capabilities, works from a user namespace,
many source mounts still result in one mount, cwd on a different
mount gets reset to root
- error paths: invalid flags return EINVAL
- regression: plain CLONE_NEWNS still copies the full mount tree,
other namespace unshares are unaffected
- mount properties: the root mount has the expected statmount
properties, is its own parent, and is the only entry returned by
listmount
- repeated unshare: consecutive UNSHARE_EMPTY_MNTNS calls each
produce a new namespace with a distinct mount ID
- overmount workflow: verifies the intended usage pattern of creating
an empty mount namespace with a nullfs root and then mounting tmpfs
over it to build a writable filesystem from scratch
Link: https://patch.msgid.link/20260306-work-empty-mntns-consolidated-v1-2-6eb30529bbb0@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add helper to utils.c and use it in statmount userns tests.
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/20250509133240.529330-8-amir73il@gmail.com
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Add helper to utils.c and use it in mount-notify and statmount tests.
Linking with utils.c drags in a dependecy with libcap, so add it to the
Makefile of the tests.
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://lore.kernel.org/20250509133240.529330-7-amir73il@gmail.com
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
