KFunc hid_bpf_allocate_context

v6.3

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).

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:

• BPF_PROG_TYPE_SYSCALL

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;