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