1/*	$NetBSD: getif.c,v 1.5 2002/07/14 00:26:17 wiz Exp $	*/
2
3#include <sys/cdefs.h>
4#ifndef lint
5__RCSID("$NetBSD: getif.c,v 1.5 2002/07/14 00:26:17 wiz Exp $");
6#endif
7
8/*
9 * getif.c : get an interface structure
10 */
11
12#include <sys/types.h>
13#include <sys/socket.h>
14#include <sys/ioctl.h>
15#include <sys/param.h>
16
17#if defined(SUNOS) || defined(SVR4)
18#include <sys/sockio.h>
19#endif
20#ifdef	SVR4
21#include <sys/stropts.h>
22#endif
23
24#include <net/if.h>				/* for struct ifreq */
25#include <netinet/in.h>
26
27#ifndef	NO_UNISTD
28#include <unistd.h>
29#endif
30#include <syslog.h>
31#include <errno.h>
32#include <assert.h>
33
34#include "getif.h"
35#include "report.h"
36
37#ifdef	__bsdi__
38#define BSD 43
39#endif
40
41static struct ifreq ifreq[10];	/* Holds interface configuration */
42static struct ifconf ifconf;	/* points to ifreq */
43
44static int nmatch(u_char *, u_char *);
45
46/* Return a pointer to the interface struct for the passed address. */
47struct ifreq *
48getif(int s, struct in_addr *addrp)
49	      						/* socket file descriptor */
50	                      		/* destination address on interface */
51{
52	int maxmatch;
53	int len, m, incr;
54	struct ifreq *ifrq, *ifrmax;
55	struct sockaddr_in *sip;
56	char *p;
57
58	/* If no address was supplied, just return NULL. */
59	if (!addrp)
60		return (struct ifreq *) 0;
61
62	/* Get the interface config if not done already. */
63	if (ifconf.ifc_len == 0) {
64#ifdef	SVR4
65		/*
66		 * SysVr4 returns garbage if you do this the obvious way!
67		 * This one took a while to figure out... -gwr
68		 */
69		struct strioctl ioc;
70		ioc.ic_cmd = SIOCGIFCONF;
71		ioc.ic_timout = 0;
72		ioc.ic_len = sizeof(ifreq);
73		ioc.ic_dp = (char *) ifreq;
74		m = ioctl(s, I_STR, (char *) &ioc);
75		ifconf.ifc_len = ioc.ic_len;
76		ifconf.ifc_req = ifreq;
77#else	/* SVR4 */
78		ifconf.ifc_len = sizeof(ifreq);
79		ifconf.ifc_req = ifreq;
80		m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
81#endif	/* SVR4 */
82		if ((m < 0) || (ifconf.ifc_len <= 0)) {
83			report(LOG_ERR, "ioctl SIOCGIFCONF");
84			return (struct ifreq *) 0;
85		}
86	}
87	maxmatch = 7;				/* this many bits or less... */
88	ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
89	p = (char *) ifreq;
90	len = ifconf.ifc_len;
91	while (len > 0) {
92		ifrq = (struct ifreq *) p;
93		if (ifrq->ifr_addr.sa_family == AF_INET) {
94			sip = (struct sockaddr_in *) &ifrq->ifr_addr;
95			m = nmatch((u_char *)addrp, (u_char *)&(sip->sin_addr));
96			if (m > maxmatch) {
97				maxmatch = m;
98				ifrmax = ifrq;
99			}
100		}
101		/* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */
102#if (BSD - 0) < 43
103		/* BSD not defined or earlier than 4.3 */
104		incr = sizeof(*ifrq);
105#else /* NetBSD */
106		incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
107#endif /* NetBSD */
108
109		p += incr;
110		len -= incr;
111	}
112
113	return ifrmax;
114}
115
116/*
117 * Return the number of leading bits matching in the
118 * internet addresses supplied.
119 */
120static int
121nmatch(u_char *ca, u_char *cb)
122	                			/* ptrs to IP address, network order */
123{
124	u_int m = 0;				/* count of matching bits */
125	u_int n = 4;				/* bytes left, then bitmask */
126
127	/* Count matching bytes. */
128	while (n && (*ca == *cb)) {
129		ca++;
130		cb++;
131		m += 8;
132		n--;
133	}
134	/* Now count matching bits. */
135	if (n) {
136		n = 0x80;
137		while (n && ((*ca & n) == (*cb & n))) {
138			m++;
139			n >>= 1;
140		}
141	}
142	return (m);
143}
144
145/*
146 * Local Variables:
147 * tab-width: 4
148 * c-indent-level: 4
149 * c-argdecl-indent: 4
150 * c-continued-statement-offset: 4
151 * c-continued-brace-offset: -4
152 * c-label-offset: -4
153 * c-brace-offset: 0
154 * End:
155 */
156