[PATCH v2 0/3] kernfs: Add inotify IN_DELETE_SELF, IN_IGNORED support for files

["T.J. Mercier" <tjmercier@google.com>]

This series adds support for IN_DELETE_SELF and IN_IGNORED inotify
events to kernfs files.

Currently, kernfs (used by cgroup and others) supports IN_MODIFY events
but fails to notify watchers when the file is removed (e.g. during
cgroup destruction). This forces userspace monitors to maintain resource
intensive side-channels like pidfds, procfs polling, or redundant
directory watches to detect when a cgroup dies and a watched file is
removed.

By generating IN_DELETE_SELF events on destruction, we allow watchers to
rely on a single watch descriptor for the entire lifecycle of the
monitored file, reducing resource usage (file descriptors, CPU cycles)
and complexity in userspace.

The series is structured as follows:
Patch 1 refactors kernfs_elem_attr to support arbitrary event types.
Patch 2 implements the logic to generate DELETE_SELF and IGNORED events
        on file removal.
Patch 3 adds selftests to verify the new behavior.

---
Changes in v2:
Remove unused variables from new selftests per kernel test robot
Fix kernfs_type argument per Tejun
Inline checks for FS_MODIFY, FS_DELETE in kernfs_notify_workfn per Tejun

T.J. Mercier (3):
  kernfs: allow passing fsnotify event types
  kernfs: send IN_DELETE_SELF and IN_IGNORED on file deletion
  selftests: memcg: Add tests IN_DELETE_SELF and IN_IGNORED on
    memory.events

 fs/kernfs/dir.c                               |  21 +++
 fs/kernfs/file.c                              |  20 ++-
 fs/kernfs/kernfs-internal.h                   |   3 +
 include/linux/kernfs.h                        |   1 +
 .../selftests/cgroup/test_memcontrol.c        | 122 ++++++++++++++++++
 5 files changed, 161 insertions(+), 6 deletions(-)


base-commit: ba268514ea14b44570030e8ed2aef92a38679e85
-- 
2.53.0.273.g2a3d683680-goog