kernel/linux.git/tools/testing/selftests/filesystems, branch master

Merge tag 'vfs-7.1-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-04-15T02:59:25+00:00

Pull vfs mount updates from Christian Brauner: - Add FSMOUNT_NAMESPACE flag to fsmount() that creates a new mount namespace with the newly created filesystem attached to a copy of the real rootfs. This returns a namespace file descriptor instead of an O_PATH mount fd, similar to how OPEN_TREE_NAMESPACE works for open_tree(). This allows creating a new filesystem and immediately placing it in a new mount namespace in a single operation, which is useful for container runtimes and other namespace-based isolation mechanisms. This accompanies OPEN_TREE_NAMESPACE and avoids a needless detour via OPEN_TREE_NAMESPACE to get the same effect. Will be especially useful when you mount an actual filesystem to be used as the container rootfs. - Currently, creating a new mount namespace always copies the entire mount tree from the caller's namespace. For containers and sandboxes that intend to build their mount table from scratch this is wasteful: they inherit a potentially large mount tree only to immediately tear it down. This series adds support for creating a mount namespace that contains only a clone of the root mount, with none of the child mounts. Two new flags are introduced: - CLONE_EMPTY_MNTNS (0x400000000) for clone3(), using the 64-bit flag space - UNSHARE_EMPTY_MNTNS (0x00100000) for unshare() Both flags imply CLONE_NEWNS. The resulting namespace contains a single nullfs root mount with an immutable empty directory. The intended workflow is to then mount a real filesystem (e.g., tmpfs) over the root and build the mount table from there. - Allow MOVE_MOUNT_BENEATH to target the caller's rootfs, allowing to switch out the rootfs without pivot_root(2). The traditional approach to switching the rootfs involves pivot_root(2) or a chroot_fs_refs()-based mechanism that atomically updates fs->root for all tasks sharing the same fs_struct. This has consequences for fork(), unshare(CLONE_FS), and setns(). This series instead decomposes root-switching into individually atomic, locally-scoped steps: fd_tree = open_tree(-EBADF, "/newroot", OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC); fchdir(fd_tree); move_mount(fd_tree, "", AT_FDCWD, "/", MOVE_MOUNT_BENEATH | MOVE_MOUNT_F_EMPTY_PATH); chroot("."); umount2(".", MNT_DETACH); Since each step only modifies the caller's own state, the fork/unshare/setns races are eliminated by design. A key step to making this possible is to remove the locked mount restriction. Originally MOVE_MOUNT_BENEATH doesn't support mounting beneath a mount that is locked. The locked mount protects the underlying mount from being revealed. This is a core mechanism of unshare(CLONE_NEWUSER | CLONE_NEWNS). The mounts in the new mount namespace become locked. That effectively makes the new mount table useless as the caller cannot ever get rid of any of the mounts no matter how useless they are. We can lift this restriction though. We simply transfer the locked property from the top mount to the mount beneath. This works because what we care about is to protect the underlying mount aka the parent. The mount mounted between the parent and the top mount takes over the job of protecting the parent mount from the top mount mount. This leaves us free to remove the locked property from the top mount which can consequently be unmounted: unshare(CLONE_NEWUSER | CLONE_NEWNS) and we inherit a clone of procfs on /proc then currently we cannot unmount it as: umount -l /proc will fail with EINVAL because the procfs mount is locked. After this series we can now do: mount --beneath -t tmpfs tmpfs /proc umount -l /proc after which a tmpfs mount has been placed beneath the procfs mount. The tmpfs mount has become locked and the procfs mount has become unlocked. This means you can safely modify an inherited mount table after unprivileged namespace creation. Afterwards we simply make it possible to move a mount beneath the rootfs allowing to upgrade the rootfs. Removing the locked restriction makes this very useful for containers created with unshare(CLONE_NEWUSER | CLONE_NEWNS) to reshuffle an inherited mount table safely and MOVE_MOUNT_BENEATH makes it possible to switch out the rootfs instead of using the costly pivot_root(2). * tag 'vfs-7.1-rc1.mount.v2' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: selftests/namespaces: remove unused utils.h include from listns_efault_test selftests/fsmount_ns: add missing TARGETS and fix cap test selftests/empty_mntns: fix wrong CLONE_EMPTY_MNTNS hex value in comment selftests/empty_mntns: fix statmount_alloc() signature mismatch selftests/statmount: remove duplicate wait_for_pid() mount: always duplicate mount selftests/filesystems: add MOVE_MOUNT_BENEATH rootfs tests move_mount: allow MOVE_MOUNT_BENEATH on the rootfs move_mount: transfer MNT_LOCKED selftests/filesystems: add clone3 tests for empty mount namespaces selftests/filesystems: add tests for empty mount namespaces namespace: allow creating empty mount namespaces selftests: add FSMOUNT_NAMESPACE tests selftests/statmount: add statmount_alloc() helper tools: update mount.h header mount: add FSMOUNT_NAMESPACE mount: simplify __do_loopback() mount: start iterating from start of rbtree

selftests/fsmount_ns: add missing TARGETS and fix cap test

2026-04-14T07:31:07+00:00

Add missing top-level kselftest TARGETS entries for empty_mntns and fsmount_ns so that 'make kselftest' discovers and runs these tests. Fix requires_cap_sys_admin test which always SKIPped because fsopen() was called after enter_userns(), where CAP_SYS_ADMIN in the mount namespace's user_ns is unavailable. Move fsopen/fsconfig before fork so the configured fs_fd is inherited by the child, which then only needs to call fsmount() after dropping privileges. Fixes: 3ac7ea91f3d0 ("selftests: add FSMOUNT_NAMESPACE tests") Signed-off-by: Christian Brauner

selftests/empty_mntns: fix wrong CLONE_EMPTY_MNTNS hex value in comment

2026-04-14T07:30:57+00:00

CLONE_EMPTY_MNTNS is (1ULL << 37) = 0x2000000000ULL, not 0x400000000ULL. Fixes: 5b8ffd63fbd9 ("selftests/filesystems: add clone3 tests for empty mount namespaces") Signed-off-by: Christian Brauner

selftests/empty_mntns: fix statmount_alloc() signature mismatch

2026-04-14T07:30:48+00:00

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: 32f54f2bbccf ("selftests/filesystems: add tests for empty mount namespaces") Signed-off-by: Christian Brauner

selftests/statmount: remove duplicate wait_for_pid()

2026-04-14T07:30:31+00:00

Remove the local static wait_for_pid() definition from statmount_test_ns.c as it conflicts with the extern declaration in utils.h. The identical function is already provided by utils.c. Fixes: 3ac7ea91f3d0 ("selftests: add FSMOUNT_NAMESPACE tests") Cc: # mainline only Signed-off-by: Christian Brauner

Merge tag 'vfs-7.1-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-04-13T21:20:11+00:00

Pull misc vfs updates from Christian Brauner: "Features: - coredump: add tracepoint for coredump events - fs: hide file and bfile caches behind runtime const machinery Fixes: - fix architecture-specific compat_ftruncate64 implementations - dcache: Limit the minimal number of bucket to two - fs/omfs: reject s_sys_blocksize smaller than OMFS_DIR_START - fs/mbcache: cancel shrink work before destroying the cache - dcache: permit dynamic_dname()s up to NAME_MAX Cleanups: - remove or unexport unused fs_context infrastructure - trivial ->setattr cleanups - selftests/filesystems: Assume that TIOCGPTPEER is defined - writeback: fix kernel-doc function name mismatch for wb_put_many() - autofs: replace manual symlink buffer allocation in autofs_dir_symlink - init/initramfs.c: trivial fix: FSM -> Finite-state machine - fs: remove stale and duplicate forward declarations - readdir: Introduce dirent_size() - fs: Replace user_access_{begin/end} by scoped user access - kernel: acct: fix duplicate word in comment - fs: write a better comment in step_into() concerning .mnt assignment - fs: attr: fix comment formatting and spelling issues" * tag 'vfs-7.1-rc1.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (28 commits) dcache: permit dynamic_dname()s up to NAME_MAX fs: attr: fix comment formatting and spelling issues fs: hide file and bfile caches behind runtime const machinery fs: write a better comment in step_into() concerning .mnt assignment proc: rename proc_notify_change to proc_setattr proc: rename proc_setattr to proc_nochmod_setattr affs: rename affs_notify_change to affs_setattr adfs: rename adfs_notify_change to adfs_setattr hfs: update comments on hfs_inode_setattr kernel: acct: fix duplicate word in comment fs: Replace user_access_{begin/end} by scoped user access readdir: Introduce dirent_size() coredump: add tracepoint for coredump events fs: remove do_sys_truncate fs: pass on FTRUNCATE_* flags to do_truncate fs: fix archiecture-specific compat_ftruncate64 fs: remove stale and duplicate forward declarations init/initramfs.c: trivial fix: FSM -> Finite-state machine autofs: replace manual symlink buffer allocation in autofs_dir_symlink fs/mbcache: cancel shrink work before destroying the cache ...

Merge tag 'vfs-7.1-rc1.xattr' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

2026-04-13T17:10:28+00:00

Pull vfs xattr updates from Christian Brauner: "This reworks the simple_xattr infrastructure and adds support for user.* extended attributes on sockets. The simple_xattr subsystem currently uses an rbtree protected by a reader-writer spinlock. This series replaces the rbtree with an rhashtable giving O(1) average-case lookup with RCU-based lockless reads. This sped up concurrent access patterns on tmpfs quite a bit and it's an overall easy enough conversion to do and gets rid or rwlock_t. The conversion is done incrementally: a new rhashtable path is added alongside the existing rbtree, consumers are migrated one at a time (shmem, kernfs, pidfs), and then the rbtree code is removed. All three consumers switch from embedded structs to pointer-based lazy allocation so the rhashtable overhead is only paid for inodes that actually use xattrs. With this infrastructure in place the series adds support for user.* xattrs on sockets. Path-based AF_UNIX sockets inherit xattr support from the underlying filesystem (e.g. tmpfs) but sockets in sockfs - that is everything created via socket() including abstract namespace AF_UNIX sockets - had no xattr support at all. The xattr_permission() checks are reworked to allow user.* xattrs on S_IFSOCK inodes. Sockfs sockets get per-inode limits of 128 xattrs and 128KB total value size matching the limits already in use for kernfs. The practical motivation comes from several directions. systemd and GNOME are expanding their use of Varlink as an IPC mechanism. For D-Bus there are tools like dbus-monitor that can observe IPC traffic across the system but this only works because D-Bus has a central broker. For Varlink there is no broker and there is currently no way to identify which sockets speak Varlink. With user.* xattrs on sockets a service can label its socket with the IPC protocol it speaks (e.g., user.varlink=1) and an eBPF program can then selectively capture traffic on those sockets. Enumerating bound sockets via netlink combined with these xattr labels gives a way to discover all Varlink IPC entrypoints for debugging and introspection. Similarly, systemd-journald wants to use xattrs on the /dev/log socket for protocol negotiation to indicate whether RFC 5424 structured syslog is supported or whether only the legacy RFC 3164 format should be used. In containers these labels are particularly useful as high-privilege or more complicated solutions for socket identification aren't available. The series comes with comprehensive selftests covering path-based AF_UNIX sockets, sockfs socket operations, per-inode limit enforcement, and xattr operations across multiple address families (AF_INET, AF_INET6, AF_NETLINK, AF_PACKET)" * tag 'vfs-7.1-rc1.xattr' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: selftests/xattr: test xattrs on various socket families selftests/xattr: sockfs socket xattr tests selftests/xattr: path-based AF_UNIX socket xattr tests xattr: support extended attributes on sockets xattr,net: support limited amount of extended attributes on sockfs sockets xattr: move user limits for xattrs to generic infra xattr: switch xattr_permission() to switch statement xattr: add xattr_permission_error() xattr: remove rbtree-based simple_xattr infrastructure pidfs: adapt to rhashtable-based simple_xattrs kernfs: adapt to rhashtable-based simple_xattrs with lazy allocation shmem: adapt to rhashtable-based simple_xattrs with lazy allocation xattr: add rhashtable-based simple_xattr infrastructure xattr: add rcu_head and rhash_head to struct simple_xattr

selftests/filesystems: add MOVE_MOUNT_BENEATH rootfs tests

2026-03-12T12:34:59+00:00

Add tests for mounting beneath the rootfs using MOVE_MOUNT_BENEATH: - beneath_rootfs_success: mount beneath /, fchdir, chroot, umount2 MNT_DETACH -- verify root changed - beneath_rootfs_old_root_stacked: after mount-beneath, verify old root parent is clone via statmount - beneath_rootfs_in_chroot_fail: chroot into subdir of same mount, mount-beneath fails (dentry != mnt_root) - beneath_rootfs_in_chroot_success: chroot into separate tmpfs mount, mount-beneath succeeds - beneath_rootfs_locked_transfer: in user+mount ns: mount-beneath rootfs succeeds, MNT_LOCKED transfers, old root unmountable - beneath_rootfs_locked_containment: in user+mount ns: after full root-switch workflow, new root is MNT_LOCKED (containment preserved) - beneath_non_rootfs_locked_transfer: mounts created before unshare(CLONE_NEWUSER | CLONE_NEWNS) become locked; mount-beneath transfers MNT_LOCKED, displaced mount can be unmounted - beneath_non_rootfs_locked_containment: same setup, verify new mount is MNT_LOCKED (containment preserved) Link: https://patch.msgid.link/20260224-work-mount-beneath-rootfs-v1-3-8c58bf08488f@kernel.org Signed-off-by: Christian Brauner

selftests/filesystems: add clone3 tests for empty mount namespaces

2026-03-12T12:33:55+00:00

Add a test suite for the CLONE_EMPTY_MNTNS flag exercising the empty mount namespace functionality through the clone3() syscall. The clone3() code path is distinct from the unshare() path already tested in empty_mntns_test.c. With clone3(), CLONE_EMPTY_MNTNS (0x400000000ULL) is a 64-bit flag that implies CLONE_NEWNS. The implication happens in kernel_clone() before copy_process(), unlike unshare() where it goes through UNSHARE_EMPTY_MNTNS to CLONE_EMPTY_MNTNS conversion in unshare_nsproxy_namespaces(). The tests cover: - basic functionality: clone3 child gets empty mount namespace with exactly one mount, root and cwd point to the same mount - CLONE_NEWNS implication: CLONE_EMPTY_MNTNS works without explicit CLONE_NEWNS, also works with redundant CLONE_NEWNS - flag interactions: combines correctly with CLONE_NEWUSER, CLONE_NEWPID, CLONE_NEWUTS, CLONE_NEWIPC, CLONE_PIDFD - mutual exclusion: CLONE_EMPTY_MNTNS | CLONE_FS returns EINVAL because the implied CLONE_NEWNS conflicts with CLONE_FS - error paths: EPERM without capabilities, unknown 64-bit flags rejected - parent isolation: parent mount namespace is unchanged after clone - many parent mounts: child still gets exactly one mount - mount properties: root mount is nullfs, is its own parent, is the only listmount entry - overmount workflow: child can mount tmpfs over nullfs root to build a writable filesystem from scratch - repeated clone3: each child gets a distinct mount namespace - setns: parent can join child's empty mount namespace via setns() - regression: plain CLONE_NEWNS via clone3 still copies the full mount tree Link: https://patch.msgid.link/20260306-work-empty-mntns-consolidated-v1-3-6eb30529bbb0@kernel.org Signed-off-by: Christian Brauner

selftests/filesystems: add tests for empty mount namespaces

2026-03-12T12:33:55+00:00

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