+ * - In some cases, the user of the bdirect interface can be allowed to modify
+ * the data in the buffer to avoid unnecessary copying. If the back-end
+ * allows such modifications, it can set can_overwrite_buffer accordingly:
+ * * 0 if no modification is allowed,
+ * * 1 if the user can modify the buffer on the condition that
+ * the modifications will be undone before calling the next
+ * fastbuf operation
+ * * 2 if the user is allowed to overwrite the data in the buffer
+ * if bdirect_read_commit_modified() is called afterwards.
+ * In this case, the back-end must be prepared for trimming
+ * of the buffer which is done by the commit function.