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getif.c revision 1.3 
      1 /*	$NetBSD: getif.c,v 1.3 1998/01/09 08:09:08 perry Exp $	*/
      2 
      3 /*
      4  * getif.c : get an interface structure
      5  */
      6 
      7 #include <sys/types.h>
      8 #include <sys/socket.h>
      9 #include <sys/ioctl.h>
     10 #include <sys/param.h>
     11 
     12 #if defined(SUNOS) || defined(SVR4)
     13 #include <sys/sockio.h>
     14 #endif
     15 #ifdef	SVR4
     16 #include <sys/stropts.h>
     17 #endif
     18 
     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 
     36 static struct ifreq ifreq[10];	/* Holds interface configuration */
     37 static struct ifconf ifconf;	/* points to ifreq */
     38 
     39 static int nmatch();
     40 
     41 /* Return a pointer to the interface struct for the passed address. */
     42 struct ifreq *
     43 getif(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(addrp, &(sip->sin_addr));
     90 		if (m > maxmatch) {
     91 			maxmatch = m;
     92 			ifrmax = ifrq;
     93 		}
     94 		/* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */
     95 #if (BSD - 0) < 43
     96 		/* BSD not defined or earlier than 4.3 */
     97 		incr = sizeof(*ifrq);
     98 #else /* NetBSD */
     99 		incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
    100 #endif /* NetBSD */
    101 
    102 		p += incr;
    103 		len -= incr;
    104 	}
    105 
    106 	return ifrmax;
    107 }
    108 
    109 /*
    110  * Return the number of leading bits matching in the
    111  * internet addresses supplied.
    112  */
    113 static int
    114 nmatch(ca, cb)
    115 	u_char *ca, *cb;			/* ptrs to IP address, network order */
    116 {
    117 	u_int m = 0;				/* count of matching bits */
    118 	u_int n = 4;				/* bytes left, then bitmask */
    119 
    120 	/* Count matching bytes. */
    121 	while (n && (*ca == *cb)) {
    122 		ca++;
    123 		cb++;
    124 		m += 8;
    125 		n--;
    126 	}
    127 	/* Now count matching bits. */
    128 	if (n) {
    129 		n = 0x80;
    130 		while (n && ((*ca & n) == (*cb & n))) {
    131 			m++;
    132 			n >>= 1;
    133 		}
    134 	}
    135 	return (m);
    136 }
    137 
    138 /*
    139  * Local Variables:
    140  * tab-width: 4
    141  * c-indent-level: 4
    142  * c-argdecl-indent: 4
    143  * c-continued-statement-offset: 4
    144  * c-continued-brace-offset: -4
    145  * c-label-offset: -4
    146  * c-brace-offset: 0
    147  * End:
    148  */
    149