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