TCP/IP协议详解卷2 第4章 以太网
这一章说是要介绍：以太网设备驱动程序在初始化后是如何接收和传输帧的；还有配置网络通用ioctl。
在ifnet中有7个函数：
/* 这是初始化等处理函数，这些函数就是我们访问网络设备驱动程序 */
int
(*if_init)
__P((
int
));
int
(*if_output)
__P((
struct
ifnet *,
struct
mbuf *,
struct
sockaddr *,
struct
rtentry *));
int
(*if_start)
__P((
struct
ifnet *));
int
(*if_done)
__P((
struct
ifnet *));
int
(*if_ioctl)
__P((
struct
ifnet *, u_long, caddr_t));
int
(*if_reset)
__P((
int
));
int
(*if_watchdog)
__P((
int
));
这7个函数就是用来调用驱动程序的。不同设备都有不同的驱动函数，比如这里说的以太网那个if_output就是ether_output
SNMP：简单网络管理协议信息库(SNMP MIB-II)
以太网封闭结构：目标地址（6） 源地址（6）协议类型（2） 共14字节 46~1500数据 CRC（4）
当设备接收到一个以太网帧，并且完整可用时，就产生中断，调用leintr，leintr调用leread把帧从接口弄到mbuf中，
所以以太网设备驱动程序将接收到的帧传给ether_input处理
leread函数第一个参数unit就是在ifnet中的那个if_unit同一类接口不同编号
leread(unit, buf, len)
int unit;
char *buf;
int len;
{
register struct le_softc *le = &le_softc[unit];
register struct ether_header *et;
struct mbuf *m;
int off, resid, flags;
le->sc_if.if_ipackets++; et = (struct ether_header *)buf; et->ether_type = ntohs((u_short)et->ether_type); /* adjust input length to account for header and CRC */ len = len - sizeof(struct ether_header) - 4;
#define ledataaddr(et, off, type) ((type)(((caddr_t)((et)+1)+(off))))
if (et->ether_type >= ETHERTYPE_TRAIL &&
et->ether_type < ETHERTYPE_TRAIL+ETHERTYPE_NTRAILER) {
off = (et->ether_type - ETHERTYPE_TRAIL) * 512;
if (off >= ETHERMTU)
return; /* sanity */
et->ether_type = ntohs(*ledataaddr(et, off, u_short *));
resid = ntohs(*(ledataaddr(et, off+2, u_short *)));
if (off + resid > len)
return; /* sanity */
len = off + resid;
} else
off = 0;
if (len <= 0) {
if (ledebug)
log(LOG_WARNING,
"le%d: ierror(runt packet): from %s: len=%d\n",
unit, ether_sprintf(et->ether_shost), len);
le->sc_runt++;
le->sc_if.if_ierrors++;
return;
}
flags = 0;
if (bcmp((caddr_t)etherbroadcastaddr,
(caddr_t)et->ether_dhost, sizeof(etherbroadcastaddr)) == 0)
flags |= M_BCAST;
if (et->ether_dhost[0] & 1)
flags |= M_MCAST;
#if NBPFILTER > 0
/*
* Check if there's a bpf filter listening on this interface.
* If so, hand off the raw packet to enet.
*/
if (le->sc_if.if_bpf) {
bpf_tap(le->sc_if.if_bpf, buf, len + sizeof(struct ether_header));
/* * Keep the packet if it's a broadcast or has our * physical ethernet address (or if we support * multicast and it's one). */ if ( #ifdef MULTICAST (flags & (M_BCAST | M_MCAST)) == 0 && #else (flags & M_BCAST) == 0 && #endif bcmp(et->ether_dhost, le->sc_addr, sizeof(et->ether_dhost)) != 0) return; } #endif /* * Pull packet off interface. Off is nonzero if packet * has trailing header; m_devget will then force this header * information to be at the front, but we still have to drop * the type and length which are at the front of any trailer data. */ m = m_devget((char *)(et + 1), len, off, &le->sc_if, 0); if (m == 0) return; m->m_flags |= flags; ether_input(&le->sc_if, et, m); }
void
ether_input(ifp, eh, m)
struct ifnet *ifp;
register struct ether_header *eh;
struct mbuf *m;
{
register struct ifqueue *inq;
register struct llc *l;
struct arpcom *ac = (struct arpcom *)ifp;
int s;
if ((ifp->if_flags & IFF_UP) == 0) {
m_freem(m);
return;
}
ifp->if_lastchange = time;
ifp->if_ibytes += m->m_pkthdr.len + sizeof (*eh);
if (bcmp((caddr_t)etherbroadcastaddr, (caddr_t)eh->ether_dhost,
sizeof(etherbroadcastaddr)) == 0)
m->m_flags |= M_BCAST;
else if (eh->ether_dhost[0] & 1)
m->m_flags |= M_MCAST;
if (m->m_flags & (M_BCAST|M_MCAST))
ifp->if_imcasts++;
switch (eh->ether_type) {
#ifdef INET
case ETHERTYPE_IP:
schednetisr(NETISR_IP);
inq = &ipintrq;
break;
case ETHERTYPE_ARP:
schednetisr(NETISR_ARP);
inq = &arpintrq;
break;
#endif
default:
if (eh->ether_type > ETHERMTU) {
m_freem(m);
return;
}
/* 下面很多都忽略掉了只留下了INET的 */
}
s = splimp();
if (IF_QFULL(inq)) {
IF_DROP(inq);
m_freem(m);
} else
IF_ENQUEUE(inq, m);
splx(s);
}
由于我其实也不知道究竟要看什么，哪些是有用的，哪些没有用，所以只能从头看下去，争取能看完一遍，之后再回来总结一下。