[Still a RFC: there are a lot of FIXMEs in the code, and calling the sleepable timer cb actually crashes.] [Also using bpf-next as the base tree as there will be conflicting changes otherwise]
This is crashing, and I have a few questions in the code (look for all of the FIXMEs), so sending this now before I become insane :)
For reference, the use cases I have in mind:
---
Basically, I need to be able to defer a HID-BPF program for the following reasons (from the aforementioned patch): 1. defer an event: Sometimes we receive an out of proximity event, but the device can not be trusted enough, and we need to ensure that we won't receive another one in the following n milliseconds. So we need to wait those n milliseconds, and eventually re-inject that event in the stack.
2. inject new events in reaction to one given event: We might want to transform one given event into several. This is the case for macro keys where a single key press is supposed to send a sequence of key presses. But this could also be used to patch a faulty behavior, if a device forgets to send a release event.
3. communicate with the device in reaction to one event: We might want to communicate back to the device after a given event. For example a device might send us an event saying that it came back from sleeping state and needs to be re-initialized.
Currently we can achieve that by keeping a userspace program around, raise a bpf event, and let that userspace program inject the events and commands. However, we are just keeping that program alive as a daemon for just scheduling commands. There is no logic in it, so it doesn't really justify an actual userspace wakeup. So a kernel workqueue seems simpler to handle.
The other part I'm not sure is whether we can say that BPF maps of type queue/stack can be used in sleepable context. I don't see any warning when running the test programs, but that's probably not a guarantee I'm doing the things properly :)
Cheers, Benjamin
To: Alexei Starovoitov ast@kernel.org To: Daniel Borkmann daniel@iogearbox.net To: John Fastabend john.fastabend@gmail.com To: Andrii Nakryiko andrii@kernel.org To: Martin KaFai Lau martin.lau@linux.dev To: Eduard Zingerman eddyz87@gmail.com To: Song Liu song@kernel.org To: Yonghong Song yonghong.song@linux.dev To: KP Singh kpsingh@kernel.org To: Stanislav Fomichev sdf@google.com To: Hao Luo haoluo@google.com To: Jiri Olsa jolsa@kernel.org To: Jiri Kosina jikos@kernel.org To: Benjamin Tissoires benjamin.tissoires@redhat.com To: Jonathan Corbet corbet@lwn.net To: Shuah Khan shuah@kernel.org Cc: bpf@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-input@vger.kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kselftest@vger.kernel.org Signed-off-by: Benjamin Tissoires bentiss@kernel.org
--- Changes in v2: - make use of bpf_timer (and dropped the custom HID handling) - implemented bpf_timer_set_sleepable_cb as a kfunc - still not implemented global subprogs - no sleepable bpf_timer selftests yet - Link to v1: https://lore.kernel.org/r/20240209-hid-bpf-sleepable-v1-0-4cc895b5adbd@kerne...
--- Benjamin Tissoires (10): bpf/verifier: introduce in_sleepable() helper bpf/helpers: introduce sleepable timers bpf/verifier: allow more maps in sleepable bpf programs HID: bpf/dispatch: regroup kfuncs definitions HID: bpf: export hid_hw_output_report as a BPF kfunc selftests/hid: Add test for hid_bpf_hw_output_report HID: bpf: allow to inject HID event from BPF selftests/hid: add tests for hid_bpf_input_report HID: bpf: allow to use bpf_timer_set_sleepable_cb() in tracing callbacks. selftests/hid: add test for bpf_timer
Documentation/hid/hid-bpf.rst | 2 +- drivers/hid/bpf/hid_bpf_dispatch.c | 232 ++++++++++++++------- drivers/hid/hid-core.c | 2 + include/linux/bpf_verifier.h | 2 + include/linux/hid_bpf.h | 3 + include/uapi/linux/bpf.h | 12 ++ kernel/bpf/helpers.c | 105 +++++++++- kernel/bpf/verifier.c | 91 +++++++- tools/testing/selftests/hid/hid_bpf.c | 195 ++++++++++++++++- tools/testing/selftests/hid/progs/hid.c | 198 ++++++++++++++++++ .../testing/selftests/hid/progs/hid_bpf_helpers.h | 8 + 11 files changed, 756 insertions(+), 94 deletions(-) --- base-commit: 4f7a05917237b006ceae760507b3d15305769ade change-id: 20240205-hid-bpf-sleepable-c01260fd91c4
Best regards,