[HID,0/7] HID: bpf: add a new hook to control hid-generic

This is a slight change from the fundamentals of HID-BPF.
In theory, HID-BPF is abstract to the kernel itself, and makes
only changes at the HID level (through report descriptors or
events emitted to/from the device).

However, we have seen a few use cases where HID-BPF might interact with
the running kernel when the target device is already handled by a
specific device.

For example, the XP-Pen/Huion/UC-Logic tablets are handled by
hid-uclogic but this driver is also doing a report descriptor fixup
without checking if the device has already been fixed by HID-BPF.

In the same way, another recent example[0] was when a cheap foot pedal is
used and tricks iPhones and Windows machines by presenting itself as a
known Apple wireless keyboard. The problem is that this fake keyboard is
not presenting a compatible report descriptor and hid-core merges all
device nodes together making libinput ignore the keyboard part for
historical reasons.

Last, there has been a long standing request to allow to disable the
input part of a given gamepad while SDL or Steam opens the device
through hidraw.

This series aims at tackling both of these problems:
- first we had a new hook `hid_bpf_driver_probe` which allows the BPF
  program to decide if the curently probed driver should be used or not
- then this same hook can also change the ->driver_data of the struct
  hid_device_id argument, and we teach hid-generic to use that field as
  the connect mask.

Basically, it means that when we insert a BPF program to fix a device,
we can force hid-generic to handle the device, and thus preventing
any other kernel driver to tamper with our device. We can also
selectively decide to export the hidraw or input nodes when using
hid-generic.

In the SDL/Steam use case, this would means that the gaming application
will load one BPF program per input device it wants to open through
hidraw, that BPF program reassigns the input device to hid-generic and
disables hid-input, then it can open the new hidraw node.
Once that program terminates, the BPF program is removed (either
automatically because no-one has the fd of the links open, or manually
by SDL/Steam), and the normal driver rebinds to the HID device,
restoring full input functionality.

This branch is on top of the for-6.12/hidraw branch of hid.git, mainly
because that branch saw some selftests/hid changes.

[0] https://gitlab.freedesktop.org/libinput/libinput/-/issues/1014

Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>
---
Benjamin Tissoires (7):
      selftests/hid: add dependency on hid_common.h
      selftests/hid: cleanup C tests by adding a common struct uhid_device
      selftests/hid: allow to parametrize bus/vid/pid/rdesc on the test device
      HID: bpf: allow BPF programs to force using hid-generic
      selftests/hid: add test for assigning a given device to hid-generic
      HID: bpf: Allow to control the connect mask of hid-generic from BPF
      selftests/hid: add test to disable hid-input

 Documentation/hid/hid-bpf.rst                      |   2 +-
 drivers/hid/bpf/hid_bpf_dispatch.c                 |  31 ++++
 drivers/hid/bpf/hid_bpf_struct_ops.c               |   4 +
 drivers/hid/hid-core.c                             |  18 +-
 drivers/hid/hid-generic.c                          |   5 +-
 include/linux/hid_bpf.h                            |  40 ++++
 tools/testing/selftests/hid/Makefile               |   2 +-
 tools/testing/selftests/hid/hid_bpf.c              | 205 ++++++++++++++++-----
 tools/testing/selftests/hid/hid_common.h           | 112 +++++++----
 tools/testing/selftests/hid/hidraw.c               |  36 +---
 tools/testing/selftests/hid/progs/hid.c            |  31 ++++
 .../testing/selftests/hid/progs/hid_bpf_helpers.h  |   4 +
 12 files changed, 372 insertions(+), 118 deletions(-)
---
base-commit: 321f7798cfb8d834ae0ed0d467c8bf46804243f9
change-id: 20240829-hid-bpf-hid-generic-61579f5b5945

Best regards,