graphics_drm.cpp 报“mmap() failer: Invalid argument” 错误

Question

调试平板的 recovery，执行下面函数时报“mmap() failer: Invalid argument” 错误，不知道错误原因是什么。具体相关变量值标注在注释里，希望高手给予指点。

static drm_surface *drm_create_surface(int width, int height) {
    struct drm_surface *surface;
    struct drm_mode_create_dumb create_dumb;
    uint32_t format;
    int ret;

    surface = (struct drm_surface*)calloc(1, sizeof(*surface));
    if (!surface) {
        printf("Can't allocate memory\n");
        return NULL;
    }

#if defined(RECOVERY_ABGR)
    format = DRM_FORMAT_RGBA8888;
#elif defined(RECOVERY_BGRA)
    format = DRM_FORMAT_ARGB8888;     //这是我的平板中的参数
#elif defined(RECOVERY_RGBX)
    format = DRM_FORMAT_XBGR8888;
#else
    format = DRM_FORMAT_RGB565;
#endif

    memset(&create_dumb, 0, sizeof(create_dumb));
    create_dumb.height = height;
    create_dumb.width = width;
    create_dumb.bpp = drm_format_to_bpp(format);
    create_dumb.flags = 0;

    ret = drmIoctl(drm_fd, DRM_IOCTL_MODE_CREATE_DUMB, &create_dumb);
    if (ret) {
        printf("DRM_IOCTL_MODE_CREATE_DUMB failed ret=%d\n",ret);
        drm_destroy_surface(surface);
        return NULL;
    }
    surface->handle = create_dumb.handle;

    uint32_t handles[4], pitches[4], offsets[4];

    handles[0] = surface->handle;
    pitches[0] = create_dumb.pitch;
    offsets[0] = 0;

    ret = drmModeAddFB2(drm_fd, width, height,
            format, handles, pitches, offsets,
            &(surface->fb_id), 0);
    if (ret) {
        printf("DRM_IOCTL_MODE_MAP_DUMB failed ret=%d\n",ret);
        drm_destroy_surface(surface);
        return NULL;;
    }

    surface->base.height = height;
    surface->base.width = width;
    surface->base.row_bytes = create_dumb.pitch;
    surface->base.pixel_bytes = create_dumb.bpp / 8;
    printf("Butterfly check mmap():baseheight= %d\n", surface->base.height);
    printf("Butterfly check mmap():baserow_bytes= %d\n", surface->base.row_bytes);
    printf("Butterfly check mmap():drm_fd= %d\n", drm_fd);
    printf("Butterfly check mmap():map_dumb.offset= %d\n", map_dumb.offset);

    surface->base.data = (unsigned char*)
                         mmap(NULL,
                              surface->base.height * surface->base.row_bytes,
                              PROT_READ | PROT_WRITE, MAP_SHARED,
                              drm_fd, map_dumb.offset);     //执行到这里，surface->base.height = 2048，surface->base.row_bytes = 3072，drm_fd＝0, map_dumb.offset＝0，并且检查了本函数所在 cpp 中与 drm_fd 相关的语句，执行均正常。
    if (surface->base.data == MAP_FAILED) {
        perror("mmap() failed");     //此时报错 “mmap() failer: Invalid argument”，本人水平有限，不知道原因
        drm_destroy_surface(surface);
        return NULL;
    }

    return surface;
}