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It can be interesting to inject events from BPF as if the event were
to come from the device.
For example, some multitouch devices do not all the time send a proximity
out event, and we might want to send it for the physical device.
Compared to uhid, we can now inject events on any physical device, not
just uhid virtual ones.
Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-5-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
We currently only export hid_hw_raw_request() as a BPF kfunc.
However, some devices require an explicit write on the Output Report
instead of the use of the control channel.
So also export hid_hw_output_report to BPF
Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-2-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
Previously, HID-BPF was relying on a bpf tracing program to be notified
when a program was released from userspace. This is error prone, as
LLVM sometimes inline the function and sometimes not.
So instead of messing up with the bpf prog ref count, we can use the
bpf_link concept which actually matches exactly what we want:
- a bpf_link represents the fact that a given program is attached to a
given HID device
- as long as the bpf_link has fd opened (either by the userspace program
still being around or by pinning the bpf object in the bpffs), the
program stays attached to the HID device
- once every user has closed the fd, we get called by
hid_bpf_link_release() that we no longer have any users, and we can
disconnect the program to the device in 2 passes: first atomically clear
the bit saying that the link is active, and then calling release_work in
a scheduled work item.
This solves entirely the problems of BPF tracing not showing up and is
definitely cleaner.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
