接前一篇文章：KWin、libdrm、DRM从上到下全过程 —— drmModeAddFBxxx（1）

上回书说到drmModeAddFB、drmModeAddFB2和drmModeAddFB2WithModifiers函数最终“三分归一统”，在内核层统一调用到drm_mode_addfb2函数。

这里我们先不急于往下分析drm_mode_addfb2函数，而是再来回顾一下之前的逐步合并统一的过程，以加深理解。如下图所示：

重点关注函数两次合并过程中同级函数的差异：

第1次合并

• DRM <——> libdrm

drmModeAddFB2(buffer->gpu()->fd(), size.width(), size.height(), buffer->format(), handles.data(), strides.data(), offsets.data(), &framebufferId, 0);

drmModeAddFB2WithModifiers(buffer->gpu()->fd(), size.width(), size.height(), buffer->format(), handles.data(), strides.data(), offsets.data(), modifier, &framebufferId, DRM_MODE_FB_MODIFIERS);

drm_public int drmModeAddFB2(int fd, uint32_t width, uint32_t height,
		uint32_t pixel_format, const uint32_t bo_handles[4],
		const uint32_t pitches[4], const uint32_t offsets[4],
		uint32_t *buf_id, uint32_t flags)
{
	return drmModeAddFB2WithModifiers(fd, width, height,
					  pixel_format, bo_handles,
					  pitches, offsets, NULL,
					  buf_id, flags);
}

drm_public int drmModeAddFB2WithModifiers(int fd, uint32_t width,
		uint32_t height, uint32_t pixel_format, const uint32_t bo_handles[4],
		const uint32_t pitches[4], const uint32_t offsets[4],
		const uint64_t modifier[4], uint32_t *buf_id, uint32_t flags)
{
    ……
}

•  libdrm <——> DRM

drm_public int drmModeAddFB(int fd, uint32_t width, uint32_t height, uint8_t depth,
                            uint8_t bpp, uint32_t pitch, uint32_t bo_handle,
                            uint32_t *buf_id)
{
	struct drm_mode_fb_cmd f;
	int ret;

	memclear(f);
	f.width  = width;
	f.height = height;
	f.pitch  = pitch;
	f.bpp    = bpp;
	f.depth  = depth;
	f.handle = bo_handle;

	if ((ret = DRM_IOCTL(fd, DRM_IOCTL_MODE_ADDFB, &f)))
		return ret;

	*buf_id = f.fb_id;
	return 0;
}

drm_public int drmModeAddFB2WithModifiers(int fd, uint32_t width,
		uint32_t height, uint32_t pixel_format, const uint32_t bo_handles[4],
		const uint32_t pitches[4], const uint32_t offsets[4],
		const uint64_t modifier[4], uint32_t *buf_id, uint32_t flags)
{
	struct drm_mode_fb_cmd2 f;
	int ret;

	memclear(f);
	f.width  = width;
	f.height = height;
	f.pixel_format = pixel_format;
	f.flags = flags;
	memcpy(f.handles, bo_handles, 4 * sizeof(bo_handles[0]));
	memcpy(f.pitches, pitches, 4 * sizeof(pitches[0]));
	memcpy(f.offsets, offsets, 4 * sizeof(offsets[0]));
	if (modifier)
		memcpy(f.modifier, modifier, 4 * sizeof(modifier[0]));

	if ((ret = DRM_IOCTL(fd, DRM_IOCTL_MODE_ADDFB2, &f)))
		return ret;

	*buf_id = f.fb_id;
	return 0;
}

第2次合并

int drm_mode_addfb_ioctl(struct drm_device *dev,
			 void *data, struct drm_file *file_priv)
{
	return drm_mode_addfb(dev, data, file_priv);
}

int drm_mode_addfb(struct drm_device *dev, struct drm_mode_fb_cmd *or,
		   struct drm_file *file_priv)
{
	struct drm_mode_fb_cmd2 r = {};
	int ret;

	……

	/* convert to new format and call new ioctl */
	r.fb_id = or->fb_id;
	r.width = or->width;
	r.height = or->height;
	r.pitches[0] = or->pitch;
	r.handles[0] = or->handle;

	ret = drm_mode_addfb2(dev, &r, file_priv);
	if (ret)
		return ret;

	or->fb_id = r.fb_id;

	return 0;
}

int drm_mode_addfb2_ioctl(struct drm_device *dev,
			  void *data, struct drm_file *file_priv)
{
#ifdef __BIG_ENDIAN
	……
#endif
	return drm_mode_addfb2(dev, data, file_priv);
}

由代码可以看到，drm_mode_addfb函数中存在由drm_mode_fb_cmd结构向drm_mode_fb_cmd2结构的转换，这样两者才能最终统一起来。

欲知后事如何，且看下回分解。