* @buffer_head: pointer to first byte of the buffer that is going to be sent
* @buffer_read_pointer: pointer to the part of the buffer being read
* @buffer_pending_bytes: bytes waiting to be sent
* @buffer_head: pointer to first byte of the buffer that is going to be sent
* @buffer_read_pointer: pointer to the part of the buffer being read
* @buffer_pending_bytes: bytes waiting to be sent