[PATCH 0/5] tracing/user_events: Add auto-del flag for events

From: Beau Belgrave
Date: Tue May 30 2023 - 19:53:22 EST

As part of the discussions for user_events aligning to be used with eBPF
it became clear [1] we needed a way to delete events without having to rely
upon the delete IOCTL. Steven suggested that we simply have an owner
for the event, however, the event can be held by more than just the
first register FD, such as perf/ftrace or additional registers. In order
to handle all those cases, we must only delete after all references are
gone from both user and kernel space.

This series adds a new register flag, USER_EVENT_REG_AUTO_DEL, which
causes the event to delete itself upon the last put reference. We cannot
fully drop the delete IOCTL, since we still want to enable events to be
registered early via dynamic_events and persist. If the auto delete flag
was used during dynamic_events, the event would delete immediately.

We have a few key events that we enable immediately after boot and are
monitored in our environments. Today this is done via dynamic events,
however, it could also be done directly via the ABI by not passing the
auto delete flag.

NOTE: I'll need to merge this work once we take these [2] [3] patches
into for-next. I'm happy to do so once they land there.

1: https://lore.kernel.org/linux-trace-kernel/20230518093600.3f119d68@xxxxxxxxxxxxxxxxxxxx/
2: https://lore.kernel.org/linux-trace-kernel/20230529032100.286534-1-sunliming@xxxxxxxxxx/
3: https://lore.kernel.org/linux-trace-kernel/20230519230741.669-1-beaub@xxxxxxxxxxxxxxxxxxx/

Beau Belgrave (5):
tracing/user_events: Store register flags on events
tracing/user_events: Track refcount consistently via put/get
tracing/user_events: Add flag to auto-delete events
tracing/user_events: Add self-test for auto-del flag
tracing/user_events: Add auto-del flag documentation

Documentation/trace/user_events.rst | 21 +-
include/uapi/linux/user_events.h | 10 +-
kernel/trace/trace_events_user.c | 183 ++++++++++++++----
.../testing/selftests/user_events/abi_test.c | 115 ++++++++++-
4 files changed, 278 insertions(+), 51 deletions(-)

base-commit: 3862f86c1529fa0016de6344eb974877b4cd3838