libdrm全解析十一 —— 源码全解析（8）

接前一篇文章：libdrm全解析十 —— 源码全解析（7）

本文参考以下博文：

DRM 驱动程序开发（VKMS）

特此致谢！

本文继续对include/drm/drm.h中实际功能宏定义进行讲解。

12. DRM_IOCTL_GEM_OPEN

第12个宏是DRM_IOCTL_GEM_OPEN，相应代码如下：

#define DRM_IOCTL_GEM_OPEN		DRM_IOWR(0x0b, struct drm_gem_open)

结合之前文章中的_IOWR(type,nr,size)的最终定义，得到如下代码：

#define DRM_IOCTL_GEM_OPEN		( ((3)  << 30) | (('d') << 8) | ((0x0b)   << 0) | ((sizeof(struct drm_gem_open)) << 16) )

struct drm_gem_open在同文件（include/drm/drm.h）中定义，代码如下：

/* DRM_IOCTL_GEM_OPEN ioctl argument type */
struct drm_gem_open {
	/** Name of object being opened */
	__u32 name;

	/** Returned handle for the object */
	__u32 handle;

	/** Returned size of the object */
	__u64 size;
};

drm_gem_open结构中的各成员的意义代码注释描述得很清楚了，在此无需赘述。

DRM_IOCTL_GEM_OPEN同样并无直接对应的Userspace API（即没有对应的封装），但是libdrm源码中有多处直接对其进行了调用，也是那些显卡对应的文件。

• amdgpu/amdgpu_bo.c中：

drm_public int amdgpu_bo_import(amdgpu_device_handle dev,
				enum amdgpu_bo_handle_type type,
				uint32_t shared_handle,
		     struct amdgpu_bo_import_result *output)
{
	struct drm_gem_open open_arg = {};
	struct amdgpu_bo *bo = NULL;
	uint32_t handle = 0, flink_name = 0;
	uint64_t alloc_size = 0;
	int r = 0;
	int dma_fd;
	uint64_t dma_buf_size = 0;

	……
	/* Open the handle. */
	switch (type) {
	case amdgpu_bo_handle_type_gem_flink_name:
		open_arg.name = shared_handle;
		r = drmIoctl(dev->flink_fd, DRM_IOCTL_GEM_OPEN, &open_arg);
		if (r)
			goto unlock;

		flink_name = shared_handle;
		handle = open_arg.handle;
		alloc_size = open_arg.size;
		if (dev->flink_fd != dev->fd) {
			r = drmPrimeHandleToFD(dev->flink_fd, handle,
					       DRM_CLOEXEC, &dma_fd);
			if (r)
				goto free_bo_handle;
			r = drmPrimeFDToHandle(dev->fd, dma_fd, &handle);
			close(dma_fd);
			if (r)
				goto free_bo_handle;
			r = drmCloseBufferHandle(dev->flink_fd,
						 open_arg.handle);
			if (r)
				goto free_bo_handle;
		}
		open_arg.handle = 0;
		break;

	case amdgpu_bo_handle_type_dma_buf_fd:
		handle = shared_handle;
		alloc_size = dma_buf_size;
		break;

	case amdgpu_bo_handle_type_kms:
	case amdgpu_bo_handle_type_kms_noimport:
		assert(0); /* unreachable */
	}

	……
	return r;
}

• etnaviv/etnaviv_bo.c中：

/* import a buffer object from DRI2 name */
drm_public struct etna_bo *etna_bo_from_name(struct etna_device *dev,
		uint32_t name)
{
	struct etna_bo *bo;
	struct drm_gem_open req = {
		.name = name,
	};

	pthread_mutex_lock(&table_lock);

	/* check name table first, to see if bo is already open: */
	bo = lookup_bo(dev->name_table, name);
	if (bo)
		goto out_unlock;

	if (drmIoctl(dev->fd, DRM_IOCTL_GEM_OPEN, &req)) {
		ERROR_MSG("gem-open failed: %s", strerror(errno));
		goto out_unlock;
	}

	bo = lookup_bo(dev->handle_table, req.handle);
	if (bo)
		goto out_unlock;

	bo = bo_from_handle(dev, req.size, req.handle, 0);
	if (bo)
		set_name(bo, name);

out_unlock:
	pthread_mutex_unlock(&table_lock);

	return bo;
}

• exynos/exynos_drm.c中：

/*
 * Get a exynos buffer object from a gem global object name.
 *
 * @dev: a exynos device object.
 * @name: a gem global object name exported by another process.
 *
 * this interface is used to get a exynos buffer object from a gem
 * global object name sent by another process for buffer sharing.
 *
 * if true, return a exynos buffer object else NULL.
 *
 */
drm_public struct exynos_bo *
exynos_bo_from_name(struct exynos_device *dev, uint32_t name)
{
	struct exynos_bo *bo;
	struct drm_gem_open req = {
		.name = name,
	};

	bo = calloc(sizeof(*bo), 1);
	if (!bo) {
		fprintf(stderr, "failed to allocate bo[%s].\n",
				strerror(errno));
		return NULL;
	}

	if (drmIoctl(dev->fd, DRM_IOCTL_GEM_OPEN, &req)) {
		fprintf(stderr, "failed to open gem object[%s].\n",
				strerror(errno));
		goto err_free_bo;
	}

	bo->dev = dev;
	bo->name = name;
	bo->handle = req.handle;

	return bo;

err_free_bo:
	free(bo);
	return NULL;
}

• freedreno/freedreno_bo.c中：

drm_public struct fd_bo * fd_bo_from_name(struct fd_device *dev, uint32_t name)
{
	struct drm_gem_open req = {
			.name = name,
	};
	struct fd_bo *bo;

	pthread_mutex_lock(&table_lock);

	/* check name table first, to see if bo is already open: */
	bo = lookup_bo(dev->name_table, name);
	if (bo)
		goto out_unlock;

	if (drmIoctl(dev->fd, DRM_IOCTL_GEM_OPEN, &req)) {
		ERROR_MSG("gem-open failed: %s", strerror(errno));
		goto out_unlock;
	}

	bo = lookup_bo(dev->handle_table, req.handle);
	if (bo)
		goto out_unlock;

	bo = bo_from_handle(dev, req.size, req.handle);
	if (bo) {
		set_name(bo, name);
		VG_BO_ALLOC(bo);
	}

out_unlock:
	pthread_mutex_unlock(&table_lock);

	return bo;
}

• intel/intel_bufmgr_gem.c中：

/**
 * Returns a drm_intel_bo wrapping the given buffer object handle.
 *
 * This can be used when one application needs to pass a buffer object
 * to another.
 */
drm_public drm_intel_bo *
drm_intel_bo_gem_create_from_name(drm_intel_bufmgr *bufmgr,
				  const char *name,
				  unsigned int handle)
{
	drm_intel_bufmgr_gem *bufmgr_gem = (drm_intel_bufmgr_gem *) bufmgr;
	drm_intel_bo_gem *bo_gem;
	int ret;
	struct drm_gem_open open_arg;

    ……

	memclear(open_arg);
	open_arg.name = handle;
	ret = drmIoctl(bufmgr_gem->fd,
		       DRM_IOCTL_GEM_OPEN,
		       &open_arg);
	if (ret != 0) {
		DBG("Couldn't reference %s handle 0x%08x: %s\n",
		    name, handle, strerror(errno));
		bo_gem = NULL;
		goto out;
	}
  ……
}

• nouveau/nouveau.c中：

drm_public int
nouveau_bo_name_ref(struct nouveau_device *dev, uint32_t name,
		    struct nouveau_bo **pbo)
{
	struct nouveau_drm *drm = nouveau_drm(&dev->object);
	struct nouveau_device_priv *nvdev = nouveau_device(dev);
	struct nouveau_bo_priv *nvbo;
	struct drm_gem_open req = { .name = name };
	int ret;

	pthread_mutex_lock(&nvdev->lock);
	DRMLISTFOREACHENTRY(nvbo, &nvdev->bo_list, head) {
		if (nvbo->name == name) {
			ret = nouveau_bo_wrap_locked(dev, nvbo->base.handle,
						     pbo, name);
			pthread_mutex_unlock(&nvdev->lock);
			return ret;
		}
	}

	ret = drmIoctl(drm->fd, DRM_IOCTL_GEM_OPEN, &req);
	if (ret == 0) {
		ret = nouveau_bo_wrap_locked(dev, req.handle, pbo, name);
	}

	pthread_mutex_unlock(&nvdev->lock);
	return ret;
}

• omap/omap_drm.c中：

/* import a buffer object from DRI2 name */
drm_public struct omap_bo *
omap_bo_from_name(struct omap_device *dev, uint32_t name)
{
	struct omap_bo *bo = NULL;
	struct drm_gem_open req = {
			.name = name,
	};

	pthread_mutex_lock(&table_lock);

	if (drmIoctl(dev->fd, DRM_IOCTL_GEM_OPEN, &req)) {
		goto fail;
	}

	bo = lookup_bo(dev, req.handle);
	if (!bo) {
		bo = bo_from_handle(dev, req.handle);
		bo->name = name;
	}

	pthread_mutex_unlock(&table_lock);

	return bo;

fail:
	pthread_mutex_unlock(&table_lock);
	free(bo);
	return NULL;
}

• radeon/radeon_bo_gem.c中：

每种显卡都会调用DRM_IOCTL_GEM_FLINK对应的drmIoctl。

其余宏定义将在后续文章中继续解析。

• tegra/tegra.c中：

drm_public int
drm_tegra_bo_open(struct drm_tegra *drm, uint32_t name, uint32_t flags,
                  struct drm_tegra_bo **bop)
{
    struct drm_gem_open args;
    struct drm_tegra_bo *bo;
    int err;

    bo = drm_tegra_bo_alloc(drm, 0, flags, 0);
    if (!bo)
        return -ENOMEM;

    memset(&args, 0, sizeof(args));
    args.name = name;

    err = drmIoctl(drm->fd, DRM_IOCTL_GEM_OPEN, &args);
    if (err < 0)
        goto free;

    bo->handle = args.handle;
    bo->size = args.size;

    *bop = bo;

    return 0;

free:
    free(bo);
    return err;
}

类似于DRM_IOCTL_GEM_FLINK，每种显卡都会调用DRM_IOCTL_GEM_OPEN对应的drmIoctl。

其余宏定义将在后续文章中继续解析。