drm/gem/shmem: Extract drm_gem_shmem_init() from drm_gem_shmem_create()

With gem objects in rust, the most ideal way for us to be able to handle
gem shmem object creation is to be able to handle the memory allocation of
a gem object ourselves - and then have the DRM gem shmem helpers initialize
the object we've allocated afterwards. So, let's spit out
drm_gem_shmem_init() from drm_gem_shmem_create() to allow for doing this.

Signed-off-by: Lyude Paul <lyude@redhat.com>

Author: Lyude

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -48,28 +48,12 @@ static const struct drm_gem_object_funcs drm_gem_shmem_funcs = {
 	.vm_ops = &drm_gem_shmem_vm_ops,
 };
 
-static struct drm_gem_shmem_object *
-__drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private,
-		       struct vfsmount *gemfs)
+static int __drm_gem_shmem_init(struct drm_device *dev, struct drm_gem_shmem_object *shmem,
+				size_t size, bool private, struct vfsmount *gemfs)
 {
-	struct drm_gem_shmem_object *shmem;
-	struct drm_gem_object *obj;
+	struct drm_gem_object *obj = &shmem->base;
 	int ret = 0;
 
-	size = PAGE_ALIGN(size);
-
-	if (dev->driver->gem_create_object) {
-		obj = dev->driver->gem_create_object(dev, size);
-		if (IS_ERR(obj))
-			return ERR_CAST(obj);
-		shmem = to_drm_gem_shmem_obj(obj);
-	} else {
-		shmem = kzalloc(sizeof(*shmem), GFP_KERNEL);
-		if (!shmem)
-			return ERR_PTR(-ENOMEM);
-		obj = &shmem->base;
-	}
-
 	if (!obj->funcs)
 		obj->funcs = &drm_gem_shmem_funcs;
 
@@ -81,7 +65,7 @@ __drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private,
 	}
 	if (ret) {
 		drm_gem_private_object_fini(obj);
-		goto err_free;
+		return ret;
 	}
 
 	ret = drm_gem_create_mmap_offset(obj);
@@ -102,14 +86,55 @@ __drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private,
 				     __GFP_RETRY_MAYFAIL | __GFP_NOWARN);
 	}
 
-	return shmem;
-
+	return 0;
 err_release:
 	drm_gem_object_release(obj);
-err_free:
-	kfree(obj);
+	return ret;
+}
 
-	return ERR_PTR(ret);
+/**
+ * drm_gem_shmem_init - Initialize an allocated object.
+ * @dev: DRM device
+ * @obj: The allocated shmem GEM object.
+ *
+ * Returns:
+ * 0 on success, or a negative error code on failure.
+ */
+int drm_gem_shmem_init(struct drm_device *dev, struct drm_gem_shmem_object *shmem, size_t size)
+{
+	return __drm_gem_shmem_init(dev, shmem, size, false, NULL);
+}
+EXPORT_SYMBOL_GPL(drm_gem_shmem_init);
+
+static struct drm_gem_shmem_object *
+__drm_gem_shmem_create(struct drm_device *dev, size_t size, bool private,
+		       struct vfsmount *gemfs)
+{
+	struct drm_gem_shmem_object *shmem;
+	struct drm_gem_object *obj;
+	int ret = 0;
+
+	size = PAGE_ALIGN(size);
+
+	if (dev->driver->gem_create_object) {
+		obj = dev->driver->gem_create_object(dev, size);
+		if (IS_ERR(obj))
+			return ERR_CAST(obj);
+		shmem = to_drm_gem_shmem_obj(obj);
+	} else {
+		shmem = kzalloc(sizeof(*shmem), GFP_KERNEL);
+		if (!shmem)
+			return ERR_PTR(-ENOMEM);
+		obj = &shmem->base;
+	}
+
+	ret = __drm_gem_shmem_init(dev, shmem, size, private, gemfs);
+	if (ret) {
+		kfree(obj);
+		return ERR_PTR(ret);
+	}
+
+	return shmem;
 }
 /**
  * drm_gem_shmem_create - Allocate an object with the given size

include/drm/drm_gem_shmem_helper.h

@@ -107,6 +107,7 @@ struct drm_gem_shmem_object {
 #define to_drm_gem_shmem_obj(obj) \
 	container_of(obj, struct drm_gem_shmem_object, base)
 
+int drm_gem_shmem_init(struct drm_device *dev, struct drm_gem_shmem_object *shmem, size_t size);
 struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t size);
 struct drm_gem_shmem_object *drm_gem_shmem_create_with_mnt(struct drm_device *dev,
 							   size_t size,