[PATCH RFC 0/9] pidfs: support extended attributes

[Christian Brauner <brauner@kernel.org>]

With the incoming support for permanent pidfs dentries we can start
supporting extended attributes on pidfds. This will allow to attach meta
information to tasks. This currently adds support for trusted extended
attributes which is a first natural target.

One natural extension would be to introduce a custom pidfs.* extended
attribute space and allow for the inheritance of extended attributes
across fork() and exec().

The first simple scheme will allow privileged userspace to slap tags
onto pidfds which is useful for e.g., service managers such as systemd.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
Christian Brauner (9):
      pidfs: keep pidfs dentry stashed once created
      pidfs: remove pidfs_pid_valid()
      libfs: prepare to allow for non-immutable pidfd inodes
      pidfs: make inodes mutable
      pidfs: raise SB_I_NODEV and SB_I_NOEXEC
      pidfs: support xattrs on pidfds
      selftests/pidfd: test extended attribute support
      selftests/pidfd: test extended attribute support
      selftests/pidfd: test setattr support

 fs/internal.h                                      |   2 +
 fs/libfs.c                                         |  23 +-
 fs/pidfs.c                                         | 289 ++++++++++++++++-----
 kernel/pid.c                                       |   2 +-
 tools/testing/selftests/pidfd/.gitignore           |   2 +
 tools/testing/selftests/pidfd/Makefile             |   3 +-
 tools/testing/selftests/pidfd/pidfd_setattr_test.c |  69 +++++
 tools/testing/selftests/pidfd/pidfd_xattr_test.c   | 132 ++++++++++
 8 files changed, 448 insertions(+), 74 deletions(-)
---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250617-work-pidfs-xattr-1111246fe9b2