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getif.c revision 1.1 
      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 
      9 #if defined(SUNOS) || defined(SVR4)
     10 #include <sys/sockio.h>
     11 #endif
     12 #ifdef	SVR4
     13 #include <sys/stropts.h>
     14 #endif
     15 
     16 #include <net/if.h>				/* for struct ifreq */
     17 #include <netinet/in.h>
     18 
     19 #ifndef	NO_UNISTD
     20 #include <unistd.h>
     21 #endif
     22 #include <syslog.h>
     23 #include <errno.h>
     24 #include <assert.h>
     25 
     26 #include "getif.h"
     27 #include "report.h"
     28 
     29 #ifdef	__bsdi__
     30 #define BSD 43
     31 #endif
     32 
     33 static struct ifreq ifreq[10];	/* Holds interface configuration */
     34 static struct ifconf ifconf;	/* points to ifreq */
     35 
     36 static int nmatch();
     37 
     38 /* Return a pointer to the interface struct for the passed address. */
     39 struct ifreq *
     40 getif(s, addrp)
     41 	int s;						/* socket file descriptor */
     42 	struct in_addr *addrp;		/* destination address on interface */
     43 {
     44 	int maxmatch;
     45 	int len, m, incr;
     46 	struct ifreq *ifrq, *ifrmax;
     47 	struct sockaddr_in *sip;
     48 	char *p;
     49 
     50 	/* If no address was supplied, just return NULL. */
     51 	if (!addrp)
     52 		return (struct ifreq *) 0;
     53 
     54 	/* Get the interface config if not done already. */
     55 	if (ifconf.ifc_len == 0) {
     56 #ifdef	SVR4
     57 		/*
     58 		 * SysVr4 returns garbage if you do this the obvious way!
     59 		 * This one took a while to figure out... -gwr
     60 		 */
     61 		struct strioctl ioc;
     62 		ioc.ic_cmd = SIOCGIFCONF;
     63 		ioc.ic_timout = 0;
     64 		ioc.ic_len = sizeof(ifreq);
     65 		ioc.ic_dp = (char *) ifreq;
     66 		m = ioctl(s, I_STR, (char *) &ioc);
     67 		ifconf.ifc_len = ioc.ic_len;
     68 		ifconf.ifc_req = ifreq;
     69 #else	/* SVR4 */
     70 		ifconf.ifc_len = sizeof(ifreq);
     71 		ifconf.ifc_req = ifreq;
     72 		m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
     73 #endif	/* SVR4 */
     74 		if ((m < 0) || (ifconf.ifc_len <= 0)) {
     75 			report(LOG_ERR, "ioctl SIOCGIFCONF");
     76 			return (struct ifreq *) 0;
     77 		}
     78 	}
     79 	maxmatch = 7;				/* this many bits or less... */
     80 	ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
     81 	p = (char *) ifreq;
     82 	len = ifconf.ifc_len;
     83 	while (len > 0) {
     84 		ifrq = (struct ifreq *) p;
     85 		sip = (struct sockaddr_in *) &ifrq->ifr_addr;
     86 		m = nmatch(addrp, &(sip->sin_addr));
     87 		if (m > maxmatch) {
     88 			maxmatch = m;
     89 			ifrmax = ifrq;
     90 		}
     91 		/* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */
     92 #if (BSD - 0) < 43
     93 		/* BSD not defined or earlier than 4.3 */
     94 		incr = sizeof(*ifrq);
     95 #else /* NetBSD */
     96 		incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
     97 #endif /* NetBSD */
     98 
     99 		p += incr;
    100 		len -= incr;
    101 	}
    102 
    103 	return ifrmax;
    104 }
    105 
    106 /*
    107  * Return the number of leading bits matching in the
    108  * internet addresses supplied.
    109  */
    110 static int
    111 nmatch(ca, cb)
    112 	u_char *ca, *cb;			/* ptrs to IP address, network order */
    113 {
    114 	u_int m = 0;				/* count of matching bits */
    115 	u_int n = 4;				/* bytes left, then bitmask */
    116 
    117 	/* Count matching bytes. */
    118 	while (n && (*ca == *cb)) {
    119 		ca++;
    120 		cb++;
    121 		m += 8;
    122 		n--;
    123 	}
    124 	/* Now count matching bits. */
    125 	if (n) {
    126 		n = 0x80;
    127 		while (n && ((*ca & n) == (*cb & n))) {
    128 			m++;
    129 			n >>= 1;
    130 		}
    131 	}
    132 	return (m);
    133 }
    134 
    135 /*
    136  * Local Variables:
    137  * tab-width: 4
    138  * c-indent-level: 4
    139  * c-argdecl-indent: 4
    140  * c-continued-statement-offset: 4
    141  * c-continued-brace-offset: -4
    142  * c-label-offset: -4
    143  * c-brace-offset: 0
    144  * End:
    145  */
    146