+/*
+ * Implement receive operations on a socket.
+ * We depend on the way that records are added to the sockbuf
+ * by sbappend*. In particular, each record (mbufs linked through m_next)
+ * must begin with an address if the protocol so specifies,
+ * followed by an optional mbuf containing access rights if supported
+ * by the protocol, and then zero or more mbufs of data.
+ * In order to avoid blocking network interrupts for the entire time here,
+ * we splx() while doing the actual copy to user space.
+ * Although the sockbuf is locked, new data may still be appended,
+ * and thus we must maintain consistency of the sockbuf during that time.
+ */