empty_mntns.h includes ../statmount/statmount.h which provides a
4-argument statmount_alloc(mnt_id, mnt_ns_id, mask, flags), but then
redefines its own 3-argument version without the flags parameter. This
causes a build failure due to conflicting types.
Remove the duplicate definition from empty_mntns.h and update all
callers to pass 0 for the flags argument.
Fixes: 32f54f2bbc ("selftests/filesystems: add tests for empty mount namespaces")
Signed-off-by: Christian Brauner <brauner@kernel.org>
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>
