libexec/bootpd/getif.c

   1 /*
   2  * getif.c : get an interface structure
   3  *
   4  * $FreeBSD: src/libexec/bootpd/getif.c,v 1.7 1999/08/28 00:09:18 peter Exp $
   5  */
   6
   7 #include <sys/types.h>
   8 #include <sys/socket.h>
   9 #include <sys/ioctl.h>
  10
  11 #if defined(SUNOS) || defined(SVR4)
  12 #include <sys/sockio.h>
  13 #endif
  14 #ifdef  SVR4
  15 #include <sys/stropts.h>
  16 #endif
  17
  18 #include <sys/time.h>           /* for struct timeval in net/if.h */
  19 #include <net/if.h>                             /* for struct ifreq */
  20 #include <netinet/in.h>
  21
  22 #ifndef NO_UNISTD
  23 #include <unistd.h>
  24 #endif
  25 #include <syslog.h>
  26 #include <errno.h>
  27 #include <assert.h>
  28
  29 #include "getif.h"
  30 #include "report.h"
  31
  32 #ifdef  __bsdi__
  33 #define BSD 43
  34 #endif
  35
  36 static struct ifreq ifreq[10];  /* Holds interface configuration */
  37 static struct ifconf ifconf;    /* points to ifreq */
  38
  39 static int nmatch();
  40
  41 /*
  42  * Return a pointer to the interface struct for the passed address.
  43  *
  44  * s      socket file descriptor
  45  * addrp  destination address on interface
  46  */
  47 struct ifreq *
  48 getif(int s, struct in_addr *addrp)
  49 {
  50         int maxmatch;
  51         int len, m, incr;
  52         struct ifreq *ifrq, *ifrmax;
  53         struct sockaddr_in *sip;
  54         char *p;
  55
  56         /* If no address was supplied, just return NULL. */
  57         if (!addrp)
  58                 return NULL;
  59
  60         /* Get the interface config if not done already. */
  61         if (ifconf.ifc_len == 0) {
  62 #ifdef  SVR4
  63                 /*
  64                  * SysVr4 returns garbage if you do this the obvious way!
  65                  * This one took a while to figure out... -gwr
  66                  */
  67                 struct strioctl ioc;
  68                 ioc.ic_cmd = SIOCGIFCONF;
  69                 ioc.ic_timout = 0;
  70                 ioc.ic_len = sizeof(ifreq);
  71                 ioc.ic_dp = (char *) ifreq;
  72                 m = ioctl(s, I_STR, (char *) &ioc);
  73                 ifconf.ifc_len = ioc.ic_len;
  74                 ifconf.ifc_req = ifreq;
  75 #else   /* SVR4 */
  76                 ifconf.ifc_len = sizeof(ifreq);
  77                 ifconf.ifc_req = ifreq;
  78                 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
  79 #endif  /* SVR4 */
  80                 if ((m < 0) || (ifconf.ifc_len <= 0)) {
  81                         report(LOG_ERR, "ioctl SIOCGIFCONF");
  82                         return NULL;
  83                 }
  84         }
  85         maxmatch = 7;                           /* this many bits or less... */
  86         ifrmax = NULL;                          /* ... is not a valid match  */
  87         p = (char *) ifreq;
  88         len = ifconf.ifc_len;
  89         while (len > 0) {
  90                 ifrq = (struct ifreq *) p;
  91                 sip = (struct sockaddr_in *) &ifrq->ifr_addr;
  92                 m = nmatch(addrp, &(sip->sin_addr));
  93                 if (m > maxmatch) {
  94                         maxmatch = m;
  95                         ifrmax = ifrq;
  96                 }
  97 #ifndef IFNAMSIZ
  98                 /* BSD not defined or earlier than 4.3 */
  99                 incr = sizeof(*ifrq);
 100 #else
 101                 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
 102 #endif
 103
 104                 p += incr;
 105                 len -= incr;
 106         }
 107
 108         return ifrmax;
 109 }
 110
 111 /*
 112  * Return the number of leading bits matching in the
 113  * internet addresses supplied.
 114  *
 115  * ca, cb  ptrs to IP address, network order
 116  */
 117 static int
 118 nmatch(u_char *ca, u_char *cb)
 119 {
 120         u_int m = 0;                            /* count of matching bits */
 121         u_int n = 4;                            /* bytes left, then bitmask */
 122
 123         /* Count matching bytes. */
 124         while (n && (*ca == *cb)) {
 125                 ca++;
 126                 cb++;
 127                 m += 8;
 128                 n--;
 129         }
 130         /* Now count matching bits. */
 131         if (n) {
 132                 n = 0x80;
 133                 while (n && ((*ca & n) == (*cb & n))) {
 134                         m++;
 135                         n >>= 1;
 136                 }
 137         }
 138         return (m);
 139 }