[PATCH v3 0/3] fanotify: introduce response identifier

[Ibrahim Jirdeh <ibrahimjirdeh@meta.com>]

These patches are in order to add an identifier other than fd which
can be used to respond to fanotify permission events. This is useful
for HSM use cases which are backed by a daemon to respond reliably
[1] and also for reporting pre-dir-content events without an event->fd [2]

The first few patches in the series are pulled in from Amir's work to
add support for pre-dir-content events.

In terms of testing, there are some additional LTP test cases to go with
these patches which exercise responding to events via response identifier
[3]

v2: https://lore.kernel.org/linux-fsdevel/20250710042049.3705747-1-ibrahimjirdeh@meta.com/
v1: https://lore.kernel.org/linux-fsdevel/20250623193631.2780278-1-ibrahimjirdeh@meta.com/

Changes v2 => v3:
- Add build assertions on new id fields and use union fields interchangeably


Changes v1 => v2:
- Moved away from adding a unique event identifier, and instead overload
event->fd to support a response identifier for now for FAN_REPORT_FID
setting.


[1] https://lore.kernel.org/all/CAMp4zn8aXNPzq1i8KYmbRfwDBvO5Qefa4isSyS1bwYuvkuBsHg@mail.gmail.com/
[2] https://lore.kernel.org/linux-fsdevel/2dx3pbcnv5w75fxb2ghqtsk6gzl6cuxmd2rinzwbq7xxfjf5z7@3nqidi3mno46/
[3] https://github.com/ibrahim-jirdeh/ltp/commit/91c963eb6758b12ce70b87ec060308017bf08ccb

Amir Goldstein (2):
  fanotify: add support for a variable length permission event
  fanotify: allow pre-content events with fid info

Ibrahim Jirdeh (1):
  fanotify: introduce event response identifier

 fs/notify/fanotify/fanotify.c       |  71 +++++++++++----
 fs/notify/fanotify/fanotify.h       |  30 +++++--
 fs/notify/fanotify/fanotify_user.c  | 133 +++++++++++++++++++++-------
 include/linux/fanotify.h            |   1 +
 include/linux/fsnotify_backend.h    |   2 +
 include/uapi/linux/fanotify.h       |  14 ++-
 tools/include/uapi/linux/fanotify.h |  11 ++-
 7 files changed, 203 insertions(+), 59 deletions(-)

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2.47.1