1 /* $NetBSD: getif.c,v 1.6 2003/08/18 05:39:52 itojun Exp $ */ 2 3 #include <sys/cdefs.h> 4 #ifndef lint 5 __RCSID("$NetBSD: getif.c,v 1.6 2003/08/18 05:39:52 itojun 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 static int nmatch(u_char *, u_char *); 45 46 /* Return a pointer to the interface struct for the passed address. */ 47 struct ifreq * 48 getif(int s, struct in_addr *addrp) 49 /* socket file descriptor */ 50 /* destination address on interface */ 51 { 52 int maxmatch; 53 int len, m, incr; 54 struct ifreq *ifrq, *ifrmax; 55 struct sockaddr_in *sip; 56 char *p; 57 58 /* If no address was supplied, just return NULL. */ 59 if (!addrp) 60 return (struct ifreq *) 0; 61 62 /* Get the interface config if not done already. */ 63 if (ifconf.ifc_len == 0) { 64 #ifdef SVR4 65 /* 66 * SysVr4 returns garbage if you do this the obvious way! 67 * This one took a while to figure out... -gwr 68 */ 69 struct strioctl ioc; 70 ioc.ic_cmd = SIOCGIFCONF; 71 ioc.ic_timout = 0; 72 ioc.ic_len = sizeof(ifreq); 73 ioc.ic_dp = (char *) ifreq; 74 m = ioctl(s, I_STR, (char *) &ioc); 75 ifconf.ifc_len = ioc.ic_len; 76 ifconf.ifc_req = ifreq; 77 #else /* SVR4 */ 78 ifconf.ifc_len = sizeof(ifreq); 79 ifconf.ifc_req = ifreq; 80 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf); 81 #endif /* SVR4 */ 82 if ((m < 0) || (ifconf.ifc_len <= 0)) { 83 report(LOG_ERR, "ioctl SIOCGIFCONF"); 84 return (struct ifreq *) 0; 85 } 86 } 87 maxmatch = 7; /* this many bits or less... */ 88 ifrmax = (struct ifreq *) 0;/* ... is not a valid match */ 89 p = (char *) ifreq; 90 len = ifconf.ifc_len; 91 while (len > 0) { 92 ifrq = (struct ifreq *) p; 93 if (ifrq->ifr_addr.sa_family == AF_INET) { 94 sip = (struct sockaddr_in *) &ifrq->ifr_addr; 95 m = nmatch((u_char *)addrp, (u_char *)&(sip->sin_addr)); 96 if (m > maxmatch) { 97 maxmatch = m; 98 ifrmax = ifrq; 99 } 100 } 101 /* XXX - Could this be just #ifndef IFNAMSIZ instead? -gwr */ 102 #if (BSD - 0) < 43 103 /* BSD not defined or earlier than 4.3 */ 104 incr = sizeof(*ifrq); 105 #else /* NetBSD */ 106 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ; 107 #endif /* NetBSD */ 108 109 p += incr; 110 len -= incr; 111 } 112 113 return ifrmax; 114 } 115 116 /* 117 * Return the number of leading bits matching in the 118 * internet addresses supplied. 119 */ 120 static int 121 nmatch(u_char *ca, u_char *cb) 122 /* ptrs to IP address, network order */ 123 { 124 u_int m = 0; /* count of matching bits */ 125 u_int n = 4; /* bytes left, then bitmask */ 126 127 /* Count matching bytes. */ 128 while (n && (*ca == *cb)) { 129 ca++; 130 cb++; 131 m += 8; 132 n--; 133 } 134 /* Now count matching bits. */ 135 if (n) { 136 n = 0x80; 137 while (n && ((*ca & n) == (*cb & n))) { 138 m++; 139 n >>= 1; 140 } 141 } 142 return (m); 143 } 144 145 /* 146 * Local Variables: 147 * tab-width: 4 148 * c-indent-level: 4 149 * c-argdecl-indent: 4 150 * c-continued-statement-offset: 4 151 * c-continued-brace-offset: -4 152 * c-label-offset: -4 153 * c-brace-offset: 0 154 * End: 155 */ 156