On Apr 10 2024, Benjamin Tissoires wrote: > This commit adds a fix for XPPen Artist 24 where the second button on > the pen is used as an eraser. > > It's a "feature" from Microsoft, but it turns out that it's actually > painful for artists. So we ship here a HID-BPF program that turns this > second button into an actual button. > > Note that the HID-BPF program is not directly loaded by the kernel itself > but by udev-hid-bpf[0]. But having the sources here allows us to also > integrate tests into tools/testing/selftests/hid to ensure the HID-BPF > program are actually tested. > > [0] https://gitlab.freedesktop.org/libevdev/udev-hid-bpf > > Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx> > --- > drivers/hid/bpf/progs/Makefile | 91 +++++++++++ > drivers/hid/bpf/progs/README | 102 +++++++++++++ > drivers/hid/bpf/progs/XPPen__Artist24.bpf.c | 229 ++++++++++++++++++++++++++++ > drivers/hid/bpf/progs/hid_bpf.h | 15 ++ > drivers/hid/bpf/progs/hid_bpf_helpers.h | 170 +++++++++++++++++++++ > 5 files changed, 607 insertions(+) > > diff --git a/drivers/hid/bpf/progs/Makefile b/drivers/hid/bpf/progs/Makefile > new file mode 100644 > index 000000000000..63ed7e02adf1 > --- /dev/null > +++ b/drivers/hid/bpf/progs/Makefile > @@ -0,0 +1,91 @@ > +# SPDX-License-Identifier: GPL-2.0 > +OUTPUT := .output > +abs_out := $(abspath $(OUTPUT)) > + > +CLANG ?= clang > +LLC ?= llc > +LLVM_STRIP ?= llvm-strip > + > +TOOLS_PATH := $(abspath ../../../../tools) > +BPFTOOL_SRC := $(TOOLS_PATH)/bpf/bpftool > +BPFTOOL_OUTPUT := $(abs_out)/bpftool > +DEFAULT_BPFTOOL := $(BPFTOOL_OUTPUT)/bootstrap/bpftool > +BPFTOOL ?= $(DEFAULT_BPFTOOL) > + > +LIBBPF_SRC := $(TOOLS_PATH)/lib/bpf > +LIBBPF_OUTPUT := $(abs_out)/libbpf > +LIBBPF_DESTDIR := $(LIBBPF_OUTPUT) > +LIBBPF_INCLUDE := $(LIBBPF_DESTDIR)/include > +BPFOBJ := $(LIBBPF_OUTPUT)/libbpf.a > + > +INCLUDES := -I$(OUTPUT) -I$(LIBBPF_INCLUDE) -I$(TOOLS_PATH)/include/uapi > +CFLAGS := -g -Wall > + > +VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux) \ > + $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux) \ > + ../../../../vmlinux \ > + /sys/kernel/btf/vmlinux \ > + /boot/vmlinux-$(shell uname -r) > +VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS)))) > +ifeq ($(VMLINUX_BTF),) > +$(error Cannot find a vmlinux for VMLINUX_BTF at any of "$(VMLINUX_BTF_PATHS)") > +endif > + > +ifeq ($(V),1) > +Q = > +msg = > +else > +Q = @ > +msg = @printf ' %-8s %s%s\n' "$(1)" "$(notdir $(2))" "$(if $(3), $(3))"; > +MAKEFLAGS += --no-print-directory > +submake_extras := feature_display=0 > +endif > + > +.DELETE_ON_ERROR: > + > +.PHONY: all clean > + > +SOURCES = $(wildcard *.bpf.c) > +TARGETS = $(SOURCES:.bpf.c=.bpf.o) > + > +all: $(TARGETS) > + > +clean: > + $(call msg,CLEAN) > + $(Q)rm -rf $(OUTPUT) $(TARGETS) > + > +%.bpf.o: %.bpf.c vmlinux.h $(BPFOBJ) | $(OUTPUT) > + $(call msg,BPF,$@) > + $(Q)$(CLANG) -g -O2 --target=bpf $(INCLUDES) \ > + -c $(filter %.c,$^) -o $@ && \ > + $(LLVM_STRIP) -g $@ > + > +vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL) | $(INCLUDE_DIR) > +ifeq ($(VMLINUX_H),) > + $(call msg,GEN,,$@) > + $(Q)$(BPFTOOL) btf dump file $(VMLINUX_BTF) format c > $@ > +else > + $(call msg,CP,,$@) > + $(Q)cp "$(VMLINUX_H)" $@ > +endif > + > +$(OUTPUT) $(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT): > + $(call msg,MKDIR,$@) > + $(Q)mkdir -p $@ > + > +$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OUTPUT) > + $(Q)$(MAKE) $(submake_extras) -C $(LIBBPF_SRC) \ > + OUTPUT=$(abspath $(dir $@))/ prefix= \ > + DESTDIR=$(LIBBPF_DESTDIR) $(abspath $@) install_headers > + > +ifeq ($(CROSS_COMPILE),) > +$(DEFAULT_BPFTOOL): $(BPFOBJ) | $(BPFTOOL_OUTPUT) > + $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOL_SRC) \ > + OUTPUT=$(BPFTOOL_OUTPUT)/ \ > + LIBBPF_BOOTSTRAP_OUTPUT=$(LIBBPF_OUTPUT)/ \ > + LIBBPF_BOOTSTRAP_DESTDIR=$(LIBBPF_DESTDIR)/ bootstrap > +else > +$(DEFAULT_BPFTOOL): | $(BPFTOOL_OUTPUT) > + $(Q)$(MAKE) $(submake_extras) -C $(BPFTOOL_SRC) \ > + OUTPUT=$(BPFTOOL_OUTPUT)/ bootstrap > +endif > diff --git a/drivers/hid/bpf/progs/README b/drivers/hid/bpf/progs/README > new file mode 100644 > index 000000000000..20b0928f385b > --- /dev/null > +++ b/drivers/hid/bpf/progs/README > @@ -0,0 +1,102 @@ > +# HID-BPF programs > + > +This directory contains various fixes for devices. They add new features or > +fix some behaviors without being entirely mandatory. It is better to load them > +when you have such a device, but they should not be a requirement for a device > +to be working during the boot stage. > + > +The .bpf.c files provided here are not automatically compiled in the kernel. > +They should be loaded in the kernel by `udev-hid-bpf`: > + > +https://gitlab.freedesktop.org/libevdev/udev-hid-bpf > + > +The main reasons for these fixes to be here is to have a central place to > +"upstream" them, but also this way we can test them thanks to the HID > +selftests. > + > +Once a .bpf.c file is accepted here, it is duplicated in `udev-hid-bpf` > +in the `src/bpf/stable` directory, and distributions are encouraged to > +only ship those bpf objects. So adding a file here should eventually > +land in distributions when they update `udev-hid-bpf` > + > +## Compilation > + > +Just run `make` > + > +## Installation > + > +### Automated way > + > +Just run `sudo udev-hid-bpf install ./my-awesome-fix.bpf.o` > + > +### Manual way > + > +- copy the `.bpf.o` you want in `/etc/udev-hid-bpf/` > +- create a new udev rule to automatically load it > + > +The following should do the trick (assuming udev-hid-bpf is available in > +/usr/bin): > + > +``` > +$> cp xppen-ArtistPro16Gen2.bpf.o /etc/udev-hid-bpf/ > +$> udev-hid-bpf inspect xppen-ArtistPro16Gen2.bpf.o > +[ > + { > + "name": "xppen-ArtistPro16Gen2.bpf.o", > + "devices": [ > + { > + "bus": "0x0003", > + "group": "0x0001", > + "vid": "0x28BD", > + "pid": "0x095A" > + }, > + { > + "bus": "0x0003", > + "group": "0x0001", > + "vid": "0x28BD", > + "pid": "0x095B" > + } > + ], > +... > +$> cat <EOF > /etc/udev/rules.d/99-load-hid-bpf-xppen-ArtistPro16Gen2.rules > +ACTION!="add|remove", GOTO="hid_bpf_end" > +SUBSYSTEM!="hid", GOTO="hid_bpf_end" > + > +# xppen-ArtistPro16Gen2.bpf.o > +ACTION=="add",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095A", RUN{program}+="/usr/local/bin/udev-hid-bpf add $sys$devpath /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o" > +ACTION=="remove",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095A", RUN{program}+="/usr/local/bin/udev-hid-bpf remove $sys$devpath " > +# xppen-ArtistPro16Gen2.bpf.o > +ACTION=="add",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095B", RUN{program}+="/usr/local/bin/udev-hid-bpf add $sys$devpath /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o" > +ACTION=="remove",ENV{MODALIAS}=="hid:b0003g0001v000028BDp0000095B", RUN{program}+="/usr/local/bin/udev-hid-bpf remove $sys$devpath " > + > +LABEL="hid_bpf_end" > +EOF > +$> udevadm control --reload > +``` > + > +Then unplug and replug the device. > + > +## Checks > + > +### udev rule > + > +You can check that the udev rule is correctly working by issuing > + > +``` > +$> udevadm test /sys/bus/hid/devices/0003:28BD:095B* > +... > +run: '/usr/local/bin/udev-hid-bpf add /sys/devices/virtual/misc/uhid/0003:28BD:095B.0E57 /etc/udev-hid-bpf/xppen-ArtistPro16Gen2.bpf.o' > +``` > + > +### program loaded > + > +You can check that the program has been properly loaded with `bpftool` > + > +``` > +$> bpftool prog > +... > +247: tracing name xppen_16_fix_eraser tag 18d389353ed2ef07 gpl > + loaded_at 2024-03-28T16:02:28+0100 uid 0 > + xlated 120B jited 77B memlock 4096B > + btf_id 487 > +``` > diff --git a/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c b/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c > new file mode 100644 > index 000000000000..e1be6a12bb75 > --- /dev/null > +++ b/drivers/hid/bpf/progs/XPPen__Artist24.bpf.c > @@ -0,0 +1,229 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +/* Copyright (c) 2023 Benjamin Tissoires > + */ > + > +#include "vmlinux.h" > +#include "hid_bpf.h" > +#include "hid_bpf_helpers.h" > +#include <bpf/bpf_tracing.h> > + > +#define VID_UGEE 0x28BD /* VID is shared with SinoWealth and Glorious and prob others */ > +#define PID_ARTIST_24 0x093A > +#define PID_ARTIST_24_PRO 0x092D > + > +HID_BPF_CONFIG( > + HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24), > + HID_DEVICE(BUS_USB, HID_GROUP_GENERIC, VID_UGEE, PID_ARTIST_24_PRO) > +); > + > +/* > + * We need to amend the report descriptor for the following: > + * - the device reports Eraser instead of using Secondary Barrel Switch > + * - the pen doesn't have a rubber tail, so basically we are removing any > + * eraser/invert bits > + */ > +static const __u8 fixed_rdesc[] = { > + 0x05, 0x0d, // Usage Page (Digitizers) 0 > + 0x09, 0x02, // Usage (Pen) 2 > + 0xa1, 0x01, // Collection (Application) 4 > + 0x85, 0x07, // Report ID (7) 6 > + 0x09, 0x20, // Usage (Stylus) 8 > + 0xa1, 0x00, // Collection (Physical) 10 > + 0x09, 0x42, // Usage (Tip Switch) 12 > + 0x09, 0x44, // Usage (Barrel Switch) 14 > + 0x09, 0x5a, // Usage (Secondary Barrel Switch) 16 /* changed from 0x45 (Eraser) to 0x5a (Secondary Barrel Switch) */ > + 0x15, 0x00, // Logical Minimum (0) 18 > + 0x25, 0x01, // Logical Maximum (1) 20 > + 0x75, 0x01, // Report Size (1) 22 > + 0x95, 0x03, // Report Count (3) 24 > + 0x81, 0x02, // Input (Data,Var,Abs) 26 > + 0x95, 0x02, // Report Count (2) 28 > + 0x81, 0x03, // Input (Cnst,Var,Abs) 30 > + 0x09, 0x32, // Usage (In Range) 32 > + 0x95, 0x01, // Report Count (1) 34 > + 0x81, 0x02, // Input (Data,Var,Abs) 36 > + 0x95, 0x02, // Report Count (2) 38 > + 0x81, 0x03, // Input (Cnst,Var,Abs) 40 > + 0x75, 0x10, // Report Size (16) 42 > + 0x95, 0x01, // Report Count (1) 44 > + 0x35, 0x00, // Physical Minimum (0) 46 > + 0xa4, // Push 48 > + 0x05, 0x01, // Usage Page (Generic Desktop) 49 > + 0x09, 0x30, // Usage (X) 51 > + 0x65, 0x13, // Unit (EnglishLinear: in) 53 > + 0x55, 0x0d, // Unit Exponent (-3) 55 > + 0x46, 0xf0, 0x50, // Physical Maximum (20720) 57 > + 0x26, 0xff, 0x7f, // Logical Maximum (32767) 60 > + 0x81, 0x02, // Input (Data,Var,Abs) 63 > + 0x09, 0x31, // Usage (Y) 65 > + 0x46, 0x91, 0x2d, // Physical Maximum (11665) 67 > + 0x26, 0xff, 0x7f, // Logical Maximum (32767) 70 > + 0x81, 0x02, // Input (Data,Var,Abs) 73 > + 0xb4, // Pop 75 > + 0x09, 0x30, // Usage (Tip Pressure) 76 > + 0x45, 0x00, // Physical Maximum (0) 78 > + 0x26, 0xff, 0x1f, // Logical Maximum (8191) 80 > + 0x81, 0x42, // Input (Data,Var,Abs,Null) 83 > + 0x09, 0x3d, // Usage (X Tilt) 85 > + 0x15, 0x81, // Logical Minimum (-127) 87 > + 0x25, 0x7f, // Logical Maximum (127) 89 > + 0x75, 0x08, // Report Size (8) 91 > + 0x95, 0x01, // Report Count (1) 93 > + 0x81, 0x02, // Input (Data,Var,Abs) 95 > + 0x09, 0x3e, // Usage (Y Tilt) 97 > + 0x15, 0x81, // Logical Minimum (-127) 99 > + 0x25, 0x7f, // Logical Maximum (127) 101 > + 0x81, 0x02, // Input (Data,Var,Abs) 103 > + 0xc0, // End Collection 105 > + 0xc0, // End Collection 106 > +}; > + > +#define BIT(n) (1UL << n) > + > +#define TIP_SWITCH BIT(0) > +#define BARREL_SWITCH BIT(1) > +#define ERASER BIT(2) > +/* padding BIT(3) */ > +/* padding BIT(4) */ > +#define IN_RANGE BIT(5) > +/* padding BIT(6) */ > +/* padding BIT(7) */ > + > +#define U16(index) (data[index] | (data[index + 1] << 8)) > + > +SEC("fmod_ret/hid_bpf_rdesc_fixup") > +int BPF_PROG(hid_fix_rdesc_xppen_artist24, struct hid_bpf_ctx *hctx) > +{ > + __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */); > + > + if (!data) > + return 0; /* EPERM check */ > + > + __builtin_memcpy(data, fixed_rdesc, sizeof(fixed_rdesc)); > + > + return sizeof(fixed_rdesc); > +} > + > +static __u8 prev_state = 0; > + > +/* > + * There are a few cases where the device is sending wrong event > + * sequences, all related to the second button (the pen doesn't > + * have an eraser switch on the tail end): > + * > + * whenever the second button gets pressed or released, an > + * out-of-proximity event is generated and then the firmware > + * compensate for the missing state (and the firmware uses > + * eraser for that button): > + * > + * - if the pen is in range, an extra out-of-range is sent > + * when the second button is pressed/released: > + * // Pen is in range > + * E: InRange > + * > + * // Second button is pressed > + * E: > + * E: Eraser InRange > + * > + * // Second button is released > + * E: > + * E: InRange > + * > + * This case is ignored by this filter, it's "valid" > + * and userspace knows how to deal with it, there are just > + * a few out-of-prox events generated, but the user doesn´t > + * see them. > + * > + * - if the pen is in contact, 2 extra events are added when > + * the second button is pressed/released: an out of range > + * and an in range: > + * > + * // Pen is in contact > + * E: TipSwitch InRange > + * > + * // Second button is pressed > + * E: <- false release, needs to be filtered out > + * E: Eraser InRange <- false release, needs to be filtered out > + * E: TipSwitch Eraser InRange > + * > + * // Second button is released > + * E: <- false release, needs to be filtered out > + * E: InRange <- false release, needs to be filtered out > + * E: TipSwitch InRange > + * > + */ > +SEC("fmod_ret/hid_bpf_device_event") > +int BPF_PROG(xppen_24_fix_eraser, struct hid_bpf_ctx *hctx) > +{ > + __u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 10 /* size */); > + __u8 current_state, changed_state; > + bool prev_tip; > + __u16 tilt; > + > + if (!data) > + return 0; /* EPERM check */ > + > + current_state = data[1]; > + > + /* if the state is identical to previously, early return */ > + if (current_state == prev_state) > + return 0; > + > + prev_tip = !!(prev_state & TIP_SWITCH); > + > + /* > + * Illegal transition: pen is in range with the tip pressed, and > + * it goes into out of proximity. > + * > + * Ideally we should hold the event, start a timer and deliver it > + * only if the timer ends, but we are not capable of that now. > + * > + * And it doesn't matter because when we are in such cases, this > + * means we are detecting a false release. > + */ > + if ((current_state & IN_RANGE) == 0) { > + if (prev_tip) > + return HID_IGNORE_EVENT; > + return 0; > + } > + > + /* > + * XOR to only set the bits that have changed between > + * previous and current state > + */ > + changed_state = prev_state ^ current_state; > + > + /* Store the new state for future processing */ > + prev_state = current_state; > + > + /* > + * We get both a tipswitch and eraser change in the same HID report: > + * this is not an authorized transition and is unlikely to happen > + * in real life. > + * This is likely to be added by the firmware to emulate the > + * eraser mode so we can skip the event. > + */ > + if ((changed_state & (TIP_SWITCH | ERASER)) == (TIP_SWITCH | ERASER)) /* we get both a tipswitch and eraser change at the same time */ > + return HID_IGNORE_EVENT; > + > + return 0; > +} > + > +SEC("syscall") > +int probe(struct hid_bpf_probe_args *ctx) > +{ > + /* > + * The device exports 3 interfaces. > + */ > + ctx->retval = ctx->rdesc_size != 107; > + if (ctx->retval) > + ctx->retval = -EINVAL; > + > + /* ensure the kernel isn't fixed already */ > + if (ctx->rdesc[17] != 0x45) /* Eraser */ > + ctx->retval = -EINVAL; > + > + return 0; > +} > + > +char _license[] SEC("license") = "GPL"; > diff --git a/drivers/hid/bpf/progs/hid_bpf.h b/drivers/hid/bpf/progs/hid_bpf.h > new file mode 100644 > index 000000000000..7ee371cac2e1 > --- /dev/null > +++ b/drivers/hid/bpf/progs/hid_bpf.h > @@ -0,0 +1,15 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +/* Copyright (c) 2022 Benjamin Tissoires > + */ > + > +#ifndef ____HID_BPF__H > +#define ____HID_BPF__H > + > +struct hid_bpf_probe_args { > + unsigned int hid; > + unsigned int rdesc_size; > + unsigned char rdesc[4096]; > + int retval; > +}; > + > +#endif /* ____HID_BPF__H */ > diff --git a/drivers/hid/bpf/progs/hid_bpf_helpers.h b/drivers/hid/bpf/progs/hid_bpf_helpers.h > new file mode 100644 > index 000000000000..1d53b10aaa2e > --- /dev/null > +++ b/drivers/hid/bpf/progs/hid_bpf_helpers.h > @@ -0,0 +1,170 @@ > +/* SPDX-License-Identifier: GPL-2.0-only */ > +/* Copyright (c) 2022 Benjamin Tissoires > + */ > + > +#ifndef __HID_BPF_HELPERS_H > +#define __HID_BPF_HELPERS_H > + > +#include "vmlinux.h" > +#include <bpf/bpf_helpers.h> > +#include <linux/errno.h> > + > +extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx, > + unsigned int offset, > + const size_t __sz) __ksym; > +extern struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id) __ksym; > +extern void hid_bpf_release_context(struct hid_bpf_ctx *ctx) __ksym; > +extern int hid_bpf_hw_request(struct hid_bpf_ctx *ctx, > + __u8 *data, > + size_t buf__sz, > + enum hid_report_type type, > + enum hid_class_request reqtype) __ksym; > + > +#define HID_MAX_DESCRIPTOR_SIZE 4096 > +#define HID_IGNORE_EVENT -1 > + > +/* extracted from <linux/input.h> */ > +#define BUS_ANY 0x00 > +#define BUS_PCI 0x01 > +#define BUS_ISAPNP 0x02 > +#define BUS_USB 0x03 > +#define BUS_HIL 0x04 > +#define BUS_BLUETOOTH 0x05 > +#define BUS_VIRTUAL 0x06 > +#define BUS_ISA 0x10 > +#define BUS_I8042 0x11 > +#define BUS_XTKBD 0x12 > +#define BUS_RS232 0x13 > +#define BUS_GAMEPORT 0x14 > +#define BUS_PARPORT 0x15 > +#define BUS_AMIGA 0x16 > +#define BUS_ADB 0x17 > +#define BUS_I2C 0x18 > +#define BUS_HOST 0x19 > +#define BUS_GSC 0x1A > +#define BUS_ATARI 0x1B > +#define BUS_SPI 0x1C > +#define BUS_RMI 0x1D > +#define BUS_CEC 0x1E > +#define BUS_INTEL_ISHTP 0x1F > +#define BUS_AMD_SFH 0x20 > + > +/* extracted from <linux/hid.h> */ > +#define HID_GROUP_ANY 0x0000 > +#define HID_GROUP_GENERIC 0x0001 > +#define HID_GROUP_MULTITOUCH 0x0002 > +#define HID_GROUP_SENSOR_HUB 0x0003 > +#define HID_GROUP_MULTITOUCH_WIN_8 0x0004 > +#define HID_GROUP_RMI 0x0100 > +#define HID_GROUP_WACOM 0x0101 > +#define HID_GROUP_LOGITECH_DJ_DEVICE 0x0102 > +#define HID_GROUP_STEAM 0x0103 > +#define HID_GROUP_LOGITECH_27MHZ_DEVICE 0x0104 > +#define HID_GROUP_VIVALDI 0x0105 > + > +/* include/linux/mod_devicetable.h defines as (~0), but that gives us negative size arrays */ > +#define HID_VID_ANY 0x0000 > +#define HID_PID_ANY 0x0000 > + > +/* duplicated from incluse/linux/array_size.h > + */ FWIW, Peter mentioned on the matching MR on udev-hid-bpf that this comment was likely superflous: https://gitlab.freedesktop.org/libevdev/udev-hid-bpf/-/merge_requests/66#note_2365932 Cheers, Benjamin > +#define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0])) > + > +/* Helper macro to convert (foo, __LINE__) into foo134 so we can use __LINE__ for > + * field/variable names > + */ > +#define COMBINE1(X, Y) X ## Y > +#define COMBINE(X, Y) COMBINE1(X, Y) > + > +/* Macro magic: > + * __uint(foo, 123) creates a int (*foo)[1234] > + * > + * We use that macro to declare an anonymous struct with several > + * fields, each is the declaration of an pointer to an array of size > + * bus/group/vid/pid. (Because it's a pointer to such an array, actual storage > + * would be sizeof(pointer) rather than sizeof(array). Not that we ever > + * instantiate it anyway). > + * > + * This is only used for BTF introspection, we can later check "what size > + * is the bus array" in the introspection data and thus extract the bus ID > + * again. > + * > + * And we use the __LINE__ to give each of our structs a unique name so the > + * BPF program writer doesn't have to. > + * > + * $ bpftool btf dump file target/bpf/HP_Elite_Presenter.bpf.o > + * shows the inspection data, start by searching for .hid_bpf_config > + * and working backwards from that (each entry references the type_id of the > + * content). > + */ > + > +#define HID_DEVICE(b, g, ven, prod) \ > + struct { \ > + __uint(name, 0); \ > + __uint(bus, (b)); \ > + __uint(group, (g)); \ > + __uint(vid, (ven)); \ > + __uint(pid, (prod)); \ > + } COMBINE(_entry, __LINE__) > + > +/* Macro magic below is to make HID_BPF_CONFIG() look like a function call that > + * we can pass multiple HID_DEVICE() invocations in. > + * > + * For up to 16 arguments, HID_BPF_CONFIG(one, two) resolves to > + * > + * union { > + * HID_DEVICE(...); > + * HID_DEVICE(...); > + * } _device_ids SEC(".hid_bpf_config") > + * > + */ > + > +/* Returns the number of macro arguments, this expands > + * NARGS(a, b, c) to NTH_ARG(a, b, c, 15, 14, 13, .... 4, 3, 2, 1). > + * NTH_ARG always returns the 16th argument which in our case is 3. > + * > + * If we want more than 16 values _COUNTDOWN and _NTH_ARG both need to be > + * updated. > + */ > +#define _NARGS(...) _NARGS1(__VA_ARGS__, _COUNTDOWN) > +#define _NARGS1(...) _NTH_ARG(__VA_ARGS__) > + > +/* Add to this if we need more than 16 args */ > +#define _COUNTDOWN \ > + 15, 14, 13, 12, 11, 10, 9, 8, \ > + 7, 6, 5, 4, 3, 2, 1, 0 > + > +/* Return the 16 argument passed in. See _NARGS above for usage. Note this is > + * 1-indexed. > + */ > +#define _NTH_ARG( \ > + _1, _2, _3, _4, _5, _6, _7, _8, \ > + _9, _10, _11, _12, _13, _14, _15,\ > + N, ...) N > + > +/* Turns EXPAND(_ARG, a, b, c) into _ARG3(a, b, c) */ > +#define _EXPAND(func, ...) COMBINE(func, _NARGS(__VA_ARGS__)) (__VA_ARGS__) > + > +/* And now define all the ARG macros for each number of args we want to accept */ > +#define _ARG1(_1) _1; > +#define _ARG2(_1, _2) _1; _2; > +#define _ARG3(_1, _2, _3) _1; _2; _3; > +#define _ARG4(_1, _2, _3, _4) _1; _2; _3; _4; > +#define _ARG5(_1, _2, _3, _4, _5) _1; _2; _3; _4; _5; > +#define _ARG6(_1, _2, _3, _4, _5, _6) _1; _2; _3; _4; _5; _6; > +#define _ARG7(_1, _2, _3, _4, _5, _6, _7) _1; _2; _3; _4; _5; _6; _7; > +#define _ARG8(_1, _2, _3, _4, _5, _6, _7, _8) _1; _2; _3; _4; _5; _6; _7; _8; > +#define _ARG9(_1, _2, _3, _4, _5, _6, _7, _8, _9) _1; _2; _3; _4; _5; _6; _7; _8; _9; > +#define _ARG10(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; > +#define _ARG11(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; > +#define _ARG12(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; > +#define _ARG13(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d; > +#define _ARG14(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d, _e) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d; _e; > +#define _ARG15(_1, _2, _3, _4, _5, _6, _7, _8, _9, _a, _b, _c, _d, _e, _f) _1; _2; _3; _4; _5; _6; _7; _8; _9; _a; _b; _c; _d; _e; _f; > + > + > +#define HID_BPF_CONFIG(...) union { \ > + _EXPAND(_ARG, __VA_ARGS__) \ > +} _device_ids SEC(".hid_bpf_config") > + > +#endif /* __HID_BPF_HELPERS_H */ > > -- > 2.44.0 >
