usr.sbin/bootp/common/getif.c

   1 /*      $NetBSD: getif.c,v 1.5 2002/07/14 00:26:17 wiz Exp $    */
   2
   3 #include <sys/cdefs.h>
   4 #ifndef lint
   5 __RCSID("$NetBSD: getif.c,v 1.5 2002/07/14 00:26:17 wiz 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  */