KFunc hid_bpf_allocate_context
Allocate a context to the given HID device
Definition
Parameters
hid_id
: the system unique identifier of the HID device
Returns
A pointer to &struct hid_bpf_ctx on success, NULL
on error.
struct hid_bpf_ctx *hid_bpf_allocate_context(unsigned int hid_id)
Note
This kfunc returns a pointer to a refcounted object. The verifier will then ensure that the pointer to the object
is eventually released using a release kfunc, or transferred to a map using a referenced kptr
(by invoking bpf_kptr_xchg
). If not, the verifier fails the
loading of the BPF program until no lingering references remain in all possible explored states of the program.
Note
The pointer returned by the kfunc may be NULL. Hence, it forces the user to do a NULL check on the pointer returned from the kfunc before making use of it (dereferencing or passing to another helper).
Note
This function may sleep, and therefore can only be used from sleepable programs.
Usage
Docs could be improved
This part of the docs is incomplete, contributions are very welcome
Program types
The following program types can make use of this kfunc:
Example
// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (c) 2022 Benjamin Tissoires
*/
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include "hid_bpf_helpers.h"
#define HID_UP_BUTTON 0x0009
#define HID_GD_WHEEL 0x0038
SEC("fmod_ret/hid_bpf_device_event")
int BPF_PROG(hid_event, struct hid_bpf_ctx *hctx)
{
__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 9 /* size */);
if (!data)
return 0; /* EPERM check */
/* Touch */
data[1] &= 0xfd;
/* X */
data[4] = 0;
data[5] = 0;
/* Y */
data[6] = 0;
data[7] = 0;
return 0;
}
/* 72 == 360 / 5 -> 1 report every 5 degrees */
int resolution = 72;
int physical = 5;
struct haptic_syscall_args {
unsigned int hid;
int retval;
};
static __u8 haptic_data[8];
SEC("syscall")
int set_haptic(struct haptic_syscall_args *args)
{
struct hid_bpf_ctx *ctx;
const size_t size = sizeof(haptic_data);
u16 *res;
int ret;
if (size > sizeof(haptic_data))
return -7; /* -E2BIG */
ctx = hid_bpf_allocate_context(args->hid);
if (!ctx)
return -1; /* EPERM check */
haptic_data[0] = 1; /* report ID */
ret = hid_bpf_hw_request(ctx, haptic_data, size, HID_FEATURE_REPORT, HID_REQ_GET_REPORT);
bpf_printk("probed/remove event ret value: %d", ret);
bpf_printk("buf: %02x %02x %02x",
haptic_data[0],
haptic_data[1],
haptic_data[2]);
bpf_printk(" %02x %02x %02x",
haptic_data[3],
haptic_data[4],
haptic_data[5]);
bpf_printk(" %02x %02x",
haptic_data[6],
haptic_data[7]);
/* whenever resolution multiplier is not 3600, we have the fixed report descriptor */
res = (u16 *)&haptic_data[1];
if (*res != 3600) {
// haptic_data[1] = 72; /* resolution multiplier */
// haptic_data[2] = 0; /* resolution multiplier */
// haptic_data[3] = 0; /* Repeat Count */
haptic_data[4] = 3; /* haptic Auto Trigger */
// haptic_data[5] = 5; /* Waveform Cutoff Time */
// haptic_data[6] = 80; /* Retrigger Period */
// haptic_data[7] = 0; /* Retrigger Period */
} else {
haptic_data[4] = 0;
}
ret = hid_bpf_hw_request(ctx, haptic_data, size, HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
bpf_printk("set haptic ret value: %d -> %d", ret, haptic_data[4]);
args->retval = ret;
hid_bpf_release_context(ctx);
return 0;
}
/* Convert REL_DIAL into REL_WHEEL */
SEC("fmod_ret/hid_bpf_rdesc_fixup")
int BPF_PROG(hid_rdesc_fixup, struct hid_bpf_ctx *hctx)
{
__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 4096 /* size */);
__u16 *res, *phys;
if (!data)
return 0; /* EPERM check */
/* Convert TOUCH into a button */
data[31] = HID_UP_BUTTON;
data[33] = 2;
/* Convert REL_DIAL into REL_WHEEL */
data[45] = HID_GD_WHEEL;
/* Change Resolution Multiplier */
phys = (__u16 *)&data[61];
*phys = physical;
res = (__u16 *)&data[66];
*res = resolution;
/* Convert X,Y from Abs to Rel */
data[88] = 0x06;
data[98] = 0x06;
return 0;
}
char _license[] SEC("license") = "GPL";
u32 _version SEC("version") = 1;