android studio 用户空间通过 drm 向缓冲区写入数据(添加libdrm.so库)

1.从android 系统中导出libdrm.so 、libnativeloader.so 两个drm 库文件，库文件路径/system/lib；

两种方式：1）通过adb 导出，如果出现权限问题，请参考：https://blog.youkuaiyun.com/Chhjnavy/article/details/97643584

adb pull /system/lib ./   

                 2）通过android studio 的Device File Explorer 文件管理，找到/system/lib 路径下相关文件，右击save 保存到桌面；

 

2.导出相关头文件：路径android 源码根目录 /external/libdrm  下

#include "xf86drm.h"
#include "xf86drmMode.h"

3.jni 层添加c++ 文件

#include <jni.h>

//#define _GNU_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>
#include "xf86drm.h"
#include "xf86drmMode.h"

#include <android/log.h>
#define TAG "terawins" // 这个是自定义的LOG的标识
#define LOGD(...) __android_log_print(ANDROID_LOG_DEBUG,TAG ,__VA_ARGS__) // 定义LOGD类型


struct buffer_object {
    uint32_t width;
    uint32_t height;
    uint32_t pitch;
    uint32_t handle;
    uint32_t size;
    uint32_t *vaddr;
    uint32_t fb_id;
};

struct buffer_object buf[2];

static int modeset_create_fb(int fd, struct buffer_object *bo, uint32_t color)
{
    struct drm_mode_create_dumb create = {};
    struct drm_mode_map_dumb map = {};
    uint32_t i;

    create.width = bo->width;
    create.height = bo->height;
    create.bpp = 32;
    drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &create);

    bo->pitch = create.pitch;
    bo->size = create.size;
    bo->handle = create.handle;
    drmModeAddFB(fd, bo->width, bo->height, 24, 32, bo->pitch,
                 bo->handle, &bo->fb_id);

    map.handle = create.handle;
    drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &map);

    bo->vaddr = static_cast<uint32_t *>(mmap(0, create.size, PROT_READ | PROT_WRITE,
                                             MAP_SHARED, fd, map.offset));

    for (i = 0; i < (bo->size / 4); i++)
        bo->vaddr[i] = color;

    return 0;
}

static void modeset_destroy_fb(int fd, struct buffer_object *bo)
{
    struct drm_mode_destroy_dumb destroy = {};

    drmModeRmFB(fd, bo->fb_id);

    munmap(bo->vaddr, bo->size);

    destroy.handle = bo->handle;
    drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy);
}

int DRM2()
{
    int fd;
    drmModeConnector *conn;
    drmModeRes *res;
    uint32_t conn_id;
    uint32_t crtc_id;

    fd = open("/dev/dri/card0", O_RDWR | O_CLOEXEC);

    res = drmModeGetResources(fd);
    crtc_id = res->crtcs[0];
    conn_id = res->connectors[0];

    conn = drmModeGetConnector(fd, conn_id);
    buf[0].width = conn->modes[0].hdisplay;
    buf[0].height = conn->modes[0].vdisplay;
    buf[1].width = conn->modes[0].hdisplay;
    buf[1].height = conn->modes[0].vdisplay;

    modeset_create_fb(fd, &buf[0], 0xff0000);
    modeset_create_fb(fd, &buf[1], 0x0000ff);

    drmModeSetCrtc(fd, crtc_id, buf[0].fb_id,
                   0, 0, &conn_id, 1, &conn->modes[0]);

    sleep(2);

    drmModeSetCrtc(fd, crtc_id, buf[1].fb_id,
                   0, 0, &conn_id, 1, &conn->modes[0]);

*//*    getchar();

    drmModeSetCrtc(fd, crtc_id, buf[1].fb_id,
                   0, 0, &conn_id, 1, &conn->modes[0]);

    getchar();

    modeset_destroy_fb(fd, &buf[1]);
    modeset_destroy_fb(fd, &buf[0]);*//*
    sleep(2);
*//*    drmModeFreeConnector(conn);
    drmModeFreeResources(res);*//*

    //close(fd);

    return 0;
}

4.通过内存映射，将内核空间的buffer 映射到用户空间，对其操作，即可进行写操作（读操作不行，android 这个貌似不对外开放了）

参考链接：https://blog.youkuaiyun.com/hexiaolong2009/article/details/84674127