drm/vmwgfx: Look up user buffer objects without taking a reference

Identically to how we look up ttm base objects witout reference, provide
the same functionality to vmw user buffer objects which derive from them.

Signed-off-by: Thomas Hellstrom <[e-mail]>
Reviewed-by: Sinclair Yeh <[e-mail]>

drivers/gpu/drm/vmwgfx/vmwgfx_bo.c

···
 	return 0;
 }
 
+/**
+ * vmw_user_bo_noref_lookup - Look up a vmw user buffer object without reference
+ * @tfile: The TTM object file the handle is registered with.
+ * @handle: The user buffer object handle.
+ *
+ * This function looks up a struct vmw_user_bo and returns a pointer to the
+ * struct vmw_buffer_object it derives from without refcounting the pointer.
+ * The returned pointer is only valid until vmw_user_bo_noref_release() is
+ * called, and the object pointed to by the returned pointer may be doomed.
+ * Any persistent usage of the object requires a refcount to be taken using
+ * ttm_bo_reference_unless_doomed(). Iff this function returns successfully it
+ * needs to be paired with vmw_user_bo_noref_release() and no sleeping-
+ * or scheduling functions may be called inbetween these function calls.
+ *
+ * Return: A struct vmw_buffer_object pointer if successful or negative
+ * error pointer on failure.
+ */
+struct vmw_buffer_object *
+vmw_user_bo_noref_lookup(struct ttm_object_file *tfile, u32 handle)
+{
+	struct vmw_user_buffer_object *vmw_user_bo;
+	struct ttm_base_object *base;
+
+	base = ttm_base_object_noref_lookup(tfile, handle);
+	if (!base) {
+		DRM_ERROR("Invalid buffer object handle 0x%08lx.\n",
+			  (unsigned long)handle);
+		return ERR_PTR(-ESRCH);
+	}
+
+	if (unlikely(ttm_base_object_type(base) != ttm_buffer_type)) {
+		ttm_base_object_noref_release();
+		DRM_ERROR("Invalid buffer object handle 0x%08lx.\n",
+			  (unsigned long)handle);
+		return ERR_PTR(-EINVAL);
+	}
+
+	vmw_user_bo = container_of(base, struct vmw_user_buffer_object,
+				   prime.base);
+	return &vmw_user_bo->vbo;
+}
 
 /**
  * vmw_user_bo_reference - Open a handle to a vmw user buffer object.

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

···
 extern void vmw_bo_move_notify(struct ttm_buffer_object *bo,
 			       struct ttm_mem_reg *mem);
 extern void vmw_bo_swap_notify(struct ttm_buffer_object *bo);
+extern struct vmw_buffer_object *
+vmw_user_bo_noref_lookup(struct ttm_object_file *tfile, u32 handle);
+
+/**
+ * vmw_user_bo_noref_release - release a buffer object pointer looked up
+ * without reference
+ */
+static inline void vmw_user_bo_noref_release(void)
+{
+	ttm_base_object_noref_release();
+}
+
 
 /**
  * Misc Ioctl functionality - vmwgfx_ioctl.c