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getif.c revision 1.2 
      1 /*
      2  * getif.c : get an interface structure
      3  */
      4 
      5 #include <sys/types.h>
      6 #include <sys/socket.h>
      7 #include <sys/ioctl.h>
      8 #include <sys/param.h>
      9 
     10 #if defined(SUNOS) || defined(SVR4)
     11 #include <sys/sockio.h>
     12 #endif
     13 #ifdef	SVR4
     14 #include <sys/stropts.h>
     15 #endif
     16 
     17 #include <net/if.h>				/* for struct ifreq */
     18 #include <netinet/in.h>
     19 
     20 #ifndef	NO_UNISTD
     21 #include <unistd.h>
     22 #endif
     23 #include <syslog.h>
     24 #include <errno.h>
     25 #include <assert.h>
     26 
     27 #include "getif.h"
     28 #include "report.h"
     29 
     30 #ifdef	__bsdi__
     31 #define BSD 43
     32 #endif
     33 
     34 static struct ifreq ifreq[10];	/* Holds interface configuration */
     35 static struct ifconf ifconf;	/* points to ifreq */
     36 
     37 static int nmatch();
     38 
     39 /* Return a pointer to the interface struct for the passed address. */
     40 struct ifreq *
     41 getif(s, addrp)
     42 	int s;						/* socket file descriptor */
     43 	struct in_addr *addrp;		/* destination address on interface */
     44 {
     45 	int maxmatch;
     46 	int len, m, incr;
     47 	struct ifreq *ifrq, *ifrmax;
     48 	struct sockaddr_in *sip;
     49 	char *p;
     50 
     51 	/* If no address was supplied, just return NULL. */
     52 	if (!addrp)
     53 		return (struct ifreq *) 0;
     54 
     55 	/* Get the interface config if not done already. */
     56 	if (ifconf.ifc_len == 0) {
     57 #ifdef	SVR4
     58 		/*
     59 		 * SysVr4 returns garbage if you do this the obvious way!
     60 		 * This one took a while to figure out... -gwr
     61 		 */
     62 		struct strioctl ioc;
     63 		ioc.ic_cmd = SIOCGIFCONF;
     64 		ioc.ic_timout = 0;
     65 		ioc.ic_len = sizeof(ifreq);
     66 		ioc.ic_dp = (char *) ifreq;
     67 		m = ioctl(s, I_STR, (char *) &ioc);
     68 		ifconf.ifc_len = ioc.ic_len;
     69 		ifconf.ifc_req = ifreq;
     70 #else	/* SVR4 */
     71 		ifconf.ifc_len = sizeof(ifreq);
     72 		ifconf.ifc_req = ifreq;
     73 		m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
     74 #endif	/* SVR4 */
     75 		if ((m < 0) || (ifconf.ifc_len <= 0)) {
     76 			report(LOG_ERR, "ioctl SIOCGIFCONF");
     77 			return (struct ifreq *) 0;
     78 		}
     79 	}
     80 	maxmatch = 7;				/* this many bits or less... */
     81 	ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
     82 	p = (char *) ifreq;
     83 	len = ifconf.ifc_len;
     84 	while (len > 0) {
     85 		ifrq = (struct ifreq *) p;
     86 		sip = (struct sockaddr_in *) &ifrq->ifr_addr;
     87 		m = nmatch(addrp, &(sip->sin_addr));
     88 		if (m > maxmatch) {
     89 			maxmatch = m;
     90 			ifrmax = ifrq;
     91 		}
     92 		/* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */
     93 #if (BSD - 0) < 43
     94 		/* BSD not defined or earlier than 4.3 */
     95 		incr = sizeof(*ifrq);
     96 #else /* NetBSD */
     97 		incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
     98 #endif /* NetBSD */
     99 
    100 		p += incr;
    101 		len -= incr;
    102 	}
    103 
    104 	return ifrmax;
    105 }
    106 
    107 /*
    108  * Return the number of leading bits matching in the
    109  * internet addresses supplied.
    110  */
    111 static int
    112 nmatch(ca, cb)
    113 	u_char *ca, *cb;			/* ptrs to IP address, network order */
    114 {
    115 	u_int m = 0;				/* count of matching bits */
    116 	u_int n = 4;				/* bytes left, then bitmask */
    117 
    118 	/* Count matching bytes. */
    119 	while (n && (*ca == *cb)) {
    120 		ca++;
    121 		cb++;
    122 		m += 8;
    123 		n--;
    124 	}
    125 	/* Now count matching bits. */
    126 	if (n) {
    127 		n = 0x80;
    128 		while (n && ((*ca & n) == (*cb & n))) {
    129 			m++;
    130 			n >>= 1;
    131 		}
    132 	}
    133 	return (m);
    134 }
    135 
    136 /*
    137  * Local Variables:
    138  * tab-width: 4
    139  * c-indent-level: 4
    140  * c-argdecl-indent: 4
    141  * c-continued-statement-offset: 4
    142  * c-continued-brace-offset: -4
    143  * c-label-offset: -4
    144  * c-brace-offset: 0
    145  * End:
    146  */
    147