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getif.c revision 1.4 
      1 /*	$NetBSD: getif.c,v 1.4 1998/03/14 04:39:54 lukem Exp $	*/
      2 
      3 #include <sys/cdefs.h>
      4 #ifndef lint
      5 __RCSID("$NetBSD: getif.c,v 1.4 1998/03/14 04:39:54 lukem 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 
     41 static struct ifreq ifreq[10];	/* Holds interface configuration */
     42 static struct ifconf ifconf;	/* points to ifreq */
     43 
     44 #ifdef	__STDC__
     45 #define P(args) args
     46 #else
     47 #define P(args) ()
     48 #endif
     49 
     50 static int nmatch P((u_char *, u_char *));
     51 
     52 #undef P
     53 
     54 /* Return a pointer to the interface struct for the passed address. */
     55 struct ifreq *
     56 getif(s, addrp)
     57 	int s;						/* socket file descriptor */
     58 	struct in_addr *addrp;		/* destination address on interface */
     59 {
     60 	int maxmatch;
     61 	int len, m, incr;
     62 	struct ifreq *ifrq, *ifrmax;
     63 	struct sockaddr_in *sip;
     64 	char *p;
     65 
     66 	/* If no address was supplied, just return NULL. */
     67 	if (!addrp)
     68 		return (struct ifreq *) 0;
     69 
     70 	/* Get the interface config if not done already. */
     71 	if (ifconf.ifc_len == 0) {
     72 #ifdef	SVR4
     73 		/*
     74 		 * SysVr4 returns garbage if you do this the obvious way!
     75 		 * This one took a while to figure out... -gwr
     76 		 */
     77 		struct strioctl ioc;
     78 		ioc.ic_cmd = SIOCGIFCONF;
     79 		ioc.ic_timout = 0;
     80 		ioc.ic_len = sizeof(ifreq);
     81 		ioc.ic_dp = (char *) ifreq;
     82 		m = ioctl(s, I_STR, (char *) &ioc);
     83 		ifconf.ifc_len = ioc.ic_len;
     84 		ifconf.ifc_req = ifreq;
     85 #else	/* SVR4 */
     86 		ifconf.ifc_len = sizeof(ifreq);
     87 		ifconf.ifc_req = ifreq;
     88 		m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
     89 #endif	/* SVR4 */
     90 		if ((m < 0) || (ifconf.ifc_len <= 0)) {
     91 			report(LOG_ERR, "ioctl SIOCGIFCONF");
     92 			return (struct ifreq *) 0;
     93 		}
     94 	}
     95 	maxmatch = 7;				/* this many bits or less... */
     96 	ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
     97 	p = (char *) ifreq;
     98 	len = ifconf.ifc_len;
     99 	while (len > 0) {
    100 		ifrq = (struct ifreq *) p;
    101 		sip = (struct sockaddr_in *) &ifrq->ifr_addr;
    102 		m = nmatch((u_char *)addrp, (u_char *)&(sip->sin_addr));
    103 		if (m > maxmatch) {
    104 			maxmatch = m;
    105 			ifrmax = ifrq;
    106 		}
    107 		/* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */
    108 #if (BSD - 0) < 43
    109 		/* BSD not defined or earlier than 4.3 */
    110 		incr = sizeof(*ifrq);
    111 #else /* NetBSD */
    112 		incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
    113 #endif /* NetBSD */
    114 
    115 		p += incr;
    116 		len -= incr;
    117 	}
    118 
    119 	return ifrmax;
    120 }
    121 
    122 /*
    123  * Return the number of leading bits matching in the
    124  * internet addresses supplied.
    125  */
    126 static int
    127 nmatch(ca, cb)
    128 	u_char *ca, *cb;			/* ptrs to IP address, network order */
    129 {
    130 	u_int m = 0;				/* count of matching bits */
    131 	u_int n = 4;				/* bytes left, then bitmask */
    132 
    133 	/* Count matching bytes. */
    134 	while (n && (*ca == *cb)) {
    135 		ca++;
    136 		cb++;
    137 		m += 8;
    138 		n--;
    139 	}
    140 	/* Now count matching bits. */
    141 	if (n) {
    142 		n = 0x80;
    143 		while (n && ((*ca & n) == (*cb & n))) {
    144 			m++;
    145 			n >>= 1;
    146 		}
    147 	}
    148 	return (m);
    149 }
    150 
    151 /*
    152  * Local Variables:
    153  * tab-width: 4
    154  * c-indent-level: 4
    155  * c-argdecl-indent: 4
    156  * c-continued-statement-offset: 4
    157  * c-continued-brace-offset: -4
    158  * c-label-offset: -4
    159  * c-brace-offset: 0
    160  * End:
    161  */
    162