Function m_devget

freebsd/kern/uipc_mbuf.c:1058–1117

* Routine to copy from device local memory into mbufs. * Note that `off' argument is offset into first mbuf of target chain from * which to begin copying the data to. */

 * which to begin copying the data to.
 */
struct mbuf *
m_devget(char *buf, int totlen, int off, struct ifnet *ifp,
    void (*copy)(char *from, caddr_t to, u_int len))
{
	struct mbuf *m;
	struct mbuf *top = NULL, **mp = ⊤
	int len;

	if (off < 0 || off > MHLEN)
		return (NULL);

	while (totlen > 0) {
		if (top == NULL) {	/* First one, must be PKTHDR */
			if (totlen + off >= MINCLSIZE) {
				m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
				len = MCLBYTES;
			} else {
				m = m_gethdr(M_NOWAIT, MT_DATA);
				len = MHLEN;

				/* Place initial small packet/header at end of mbuf */
				if (m && totlen + off + max_linkhdr <= MHLEN) {
					m->m_data += max_linkhdr;
					len -= max_linkhdr;
				}
			}
			if (m == NULL)
				return NULL;
			m->m_pkthdr.rcvif = ifp;
			m->m_pkthdr.len = totlen;
		} else {
			if (totlen + off >= MINCLSIZE) {
				m = m_getcl(M_NOWAIT, MT_DATA, 0);
				len = MCLBYTES;
			} else {
				m = m_get(M_NOWAIT, MT_DATA);
				len = MLEN;
			}
			if (m == NULL) {
				m_freem(top);
				return NULL;
			}
		}
		if (off) {
			m->m_data += off;
			len -= off;
			off = 0;
		}
		m->m_len = len = min(totlen, len);
		if (copy)
			copy(buf, mtod(m, caddr_t), (u_int)len);
		else
			bcopy(buf, mtod(m, caddr_t), (u_int)len);
		buf += len;
		*mp = m;
		mp = &m->m_next;
		totlen -= len;
	}