Function m_copyback

freebsd/kern/uipc_mbuf.c:1124–1171

* Copy data from a buffer back into the indicated mbuf chain, * starting "off" bytes from the beginning, extending the mbuf * chain if necessary. */

 * chain if necessary.
 */
void
m_copyback(struct mbuf *m0, int off, int len, c_caddr_t cp)
{
	int mlen;
	struct mbuf *m = m0, *n;
	int totlen = 0;

	if (m0 == NULL)
		return;
	while (off > (mlen = m->m_len)) {
		off -= mlen;
		totlen += mlen;
		if (m->m_next == NULL) {
			n = m_get(M_NOWAIT, m->m_type);
			if (n == NULL)
				goto out;
			bzero(mtod(n, caddr_t), MLEN);
			n->m_len = min(MLEN, len + off);
			m->m_next = n;
		}
		m = m->m_next;
	}
	while (len > 0) {
		if (m->m_next == NULL && (len > m->m_len - off)) {
			m->m_len += min(len - (m->m_len - off),
			    M_TRAILINGSPACE(m));
		}
		mlen = min (m->m_len - off, len);
		bcopy(cp, off + mtod(m, caddr_t), (u_int)mlen);
		cp += mlen;
		len -= mlen;
		mlen += off;
		off = 0;
		totlen += mlen;
		if (len == 0)
			break;
		if (m->m_next == NULL) {
			n = m_get(M_NOWAIT, m->m_type);
			if (n == NULL)
				break;
			n->m_len = min(MLEN, len);
			m->m_next = n;
		}
		m = m->m_next;
	}
out:	if (((m = m0)->m_flags & M_PKTHDR) && (m->m_pkthdr.len < totlen))
		m->m_pkthdr.len = totlen;
}

/*
 * Append the specified data to the indicated mbuf chain,