linux-kernel - [GIT PULL 10/12 for v7.0] vfs namespace

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Message-ID: <20260206-vfs-namespace-v70-f8476aa664c3@brauner>
Date: Fri,  6 Feb 2026 17:50:06 +0100
From: Christian Brauner <brauner@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [GIT PULL 10/12 for v7.0] vfs namespace

Hey Linus,

/* Summary */

This contains the mount changes for this cycle.

statmount: accept fd as a parameter

  Extend struct mnt_id_req with a file descriptor field and a new
  STATMOUNT_BY_FD flag. When set, statmount() returns mount information for the
  mount the fd resides on — including detached mounts (unmounted via
  umount2(MNT_DETACH)). For detached mounts the STATMOUNT_MNT_POINT and
  STATMOUNT_MNT_NS_ID mask bits are cleared since neither is meaningful. The
  capability check is skipped for STATMOUNT_BY_FD since holding an fd already
  implies prior access to the mount and equivalent information is available
  through fstatfs() and /proc/pid/mountinfo without privilege. Includes
  comprehensive selftests covering both attached and detached mount cases.

fs: Remove internal old mount API code (1 patch)

  Now that every in-tree filesystem has been converted to the new mount API,
  remove all the legacy shim code in fs_context.c that handled unconverted
  filesystems. This deletes ~280 lines including legacy_init_fs_context(), the
  legacy_fs_context struct, and associated wrappers. The mount(2) syscall path
  for userspace remains untouched. Documentation references to the legacy
  callbacks are cleaned up.

mount: add OPEN_TREE_NAMESPACE (2 patches)

  Add OPEN_TREE_NAMESPACE to open_tree(). Container runtimes currently use
  CLONE_NEWNS to copy the caller's entire mount namespace — only to then
  pivot_root() and recursively unmount everything they just copied. With large
  mount tables and thousands of parallel container launches this creates
  significant contention on the namespace semaphore.

  OPEN_TREE_NAMESPACE copies only the specified mount tree (like
  OPEN_TREE_CLONE) but returns a mount namespace fd instead of a detached mount
  fd. The new namespace contains the copied tree mounted on top of a clone of
  the real rootfs. This functions as a combined unshare(CLONE_NEWNS) +
  pivot_root() in a single syscall. Works with user namespaces: an
  unshare(CLONE_NEWUSER) followed by OPEN_TREE_NAMESPACE creates a mount
  namespace owned by the new user namespace. Mount namespace file mounts are
  excluded from the copy to prevent cycles. Includes ~1000 lines of selftests.

/* Testing */

gcc (Debian 14.2.0-19) 14.2.0
Debian clang version 19.1.7 (3+b1)

No build failures or warnings were observed.

/* Conflicts */

Merge conflicts with mainline
=============================

No known conflicts.

Merge conflicts with other trees
================================

The following changes since commit 8f0b4cce4481fb22653697cced8d0d04027cb1e8:

  Linux 6.19-rc1 (2025-12-14 16:05:07 +1200)

are available in the Git repository at:

  git@...olite.kernel.org:pub/scm/linux/kernel/git/vfs/vfs tags/vfs-7.0-rc1.namespace

for you to fetch changes up to 1bce1a664ac25d37a327c433a01bc347f0a81bd6:

  Merge patch series "mount: add OPEN_TREE_NAMESPACE" (2026-01-16 19:21:40 +0100)

----------------------------------------------------------------
vfs-7.0-rc1.namespace

Please consider pulling these changes from the signed vfs-7.0-rc1.namespace tag.

Thanks!
Christian

----------------------------------------------------------------
Bhavik Sachdev (3):
      statmount: permission check should return EPERM
      statmount: accept fd as a parameter
      selftests: statmount: tests for STATMOUNT_BY_FD

Christian Brauner (4):
      Merge patch series "statmount: accept fd as a parameter"
      mount: add OPEN_TREE_NAMESPACE
      selftests/open_tree: add OPEN_TREE_NAMESPACE tests
      Merge patch series "mount: add OPEN_TREE_NAMESPACE"

Eric Sandeen (1):
      fs: Remove internal old mount API code

 Documentation/filesystems/locking.rst              |    8 -
 Documentation/filesystems/mount_api.rst            |    2 -
 Documentation/filesystems/porting.rst              |    7 +-
 Documentation/filesystems/vfs.rst                  |   58 +-
 fs/fs_context.c                                    |  208 +---
 fs/fsopen.c                                        |   10 -
 fs/internal.h                                      |    2 +-
 fs/namespace.c                                     |  265 ++++-
 fs/nsfs.c                                          |   13 +
 include/linux/fs.h                                 |    2 -
 include/linux/fs/super_types.h                     |    1 -
 include/uapi/linux/mount.h                         |   13 +-
 .../selftests/filesystems/open_tree_ns/.gitignore  |    1 +
 .../selftests/filesystems/open_tree_ns/Makefile    |   10 +
 .../filesystems/open_tree_ns/open_tree_ns_test.c   | 1030 ++++++++++++++++++++
 .../selftests/filesystems/statmount/statmount.h    |   15 +-
 .../filesystems/statmount/statmount_test.c         |  261 ++++-
 .../filesystems/statmount/statmount_test_ns.c      |  101 +-
 tools/testing/selftests/filesystems/utils.c        |   26 +
 tools/testing/selftests/filesystems/utils.h        |    1 +
 20 files changed, 1669 insertions(+), 365 deletions(-)
 create mode 100644 tools/testing/selftests/filesystems/open_tree_ns/.gitignore
 create mode 100644 tools/testing/selftests/filesystems/open_tree_ns/Makefile
 create mode 100644 tools/testing/selftests/filesystems/open_tree_ns/open_tree_ns_test.c