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  * $DragonFly: src/libexec/bootpd/getif.c,v 1.2 2003/06/17 04:27:07 dillon Exp $
   6  */
   7
   8 #include <sys/types.h>
   9 #include <sys/socket.h>
  10 #include <sys/ioctl.h>
  11
  12 #if defined(SUNOS) || defined(SVR4)
  13 #include <sys/sockio.h>
  14 #endif
  15 #ifdef  SVR4
  16 #include <sys/stropts.h>
  17 #endif
  18
  19 #include <sys/time.h>           /* for struct timeval in net/if.h */
  20 #include <net/if.h>                             /* for struct ifreq */
  21 #include <netinet/in.h>
  22
  23 #ifndef NO_UNISTD
  24 #include <unistd.h>
  25 #endif
  26 #include <syslog.h>
  27 #include <errno.h>
  28 #include <assert.h>
  29
  30 #include "getif.h"
  31 #include "report.h"
  32
  33 #ifdef  __bsdi__
  34 #define BSD 43
  35 #endif
  36
  37 static struct ifreq ifreq[10];  /* Holds interface configuration */
  38 static struct ifconf ifconf;    /* points to ifreq */
  39
  40 static int nmatch();
  41
  42 /* Return a pointer to the interface struct for the passed address. */
  43 struct ifreq *
  44 getif(s, addrp)
  45         int s;                                          /* socket file descriptor */
  46         struct in_addr *addrp;          /* destination address on interface */
  47 {
  48         int maxmatch;
  49         int len, m, incr;
  50         struct ifreq *ifrq, *ifrmax;
  51         struct sockaddr_in *sip;
  52         char *p;
  53
  54         /* If no address was supplied, just return NULL. */
  55         if (!addrp)
  56                 return (struct ifreq *) 0;
  57
  58         /* Get the interface config if not done already. */
  59         if (ifconf.ifc_len == 0) {
  60 #ifdef  SVR4
  61                 /*
  62                  * SysVr4 returns garbage if you do this the obvious way!
  63                  * This one took a while to figure out... -gwr
  64                  */
  65                 struct strioctl ioc;
  66                 ioc.ic_cmd = SIOCGIFCONF;
  67                 ioc.ic_timout = 0;
  68                 ioc.ic_len = sizeof(ifreq);
  69                 ioc.ic_dp = (char *) ifreq;
  70                 m = ioctl(s, I_STR, (char *) &ioc);
  71                 ifconf.ifc_len = ioc.ic_len;
  72                 ifconf.ifc_req = ifreq;
  73 #else   /* SVR4 */
  74                 ifconf.ifc_len = sizeof(ifreq);
  75                 ifconf.ifc_req = ifreq;
  76                 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
  77 #endif  /* SVR4 */
  78                 if ((m < 0) || (ifconf.ifc_len <= 0)) {
  79                         report(LOG_ERR, "ioctl SIOCGIFCONF");
  80                         return (struct ifreq *) 0;
  81                 }
  82         }
  83         maxmatch = 7;                           /* this many bits or less... */
  84         ifrmax = (struct ifreq *) 0;/* ... is not a valid match  */
  85         p = (char *) ifreq;
  86         len = ifconf.ifc_len;
  87         while (len > 0) {
  88                 ifrq = (struct ifreq *) p;
  89                 sip = (struct sockaddr_in *) &ifrq->ifr_addr;
  90                 m = nmatch(addrp, &(sip->sin_addr));
  91                 if (m > maxmatch) {
  92                         maxmatch = m;
  93                         ifrmax = ifrq;
  94                 }
  95 #ifndef IFNAMSIZ
  96                 /* BSD not defined or earlier than 4.3 */
  97                 incr = sizeof(*ifrq);
  98 #else
  99                 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
 100 #endif
 101
 102                 p += incr;
 103                 len -= incr;
 104         }
 105
 106         return ifrmax;
 107 }
 108
 109 /*
 110  * Return the number of leading bits matching in the
 111  * internet addresses supplied.
 112  */
 113 static int
 114 nmatch(ca, cb)
 115         u_char *ca, *cb;                        /* ptrs to IP address, network order */
 116 {
 117         u_int m = 0;                            /* count of matching bits */
 118         u_int n = 4;                            /* bytes left, then bitmask */
 119
 120         /* Count matching bytes. */
 121         while (n && (*ca == *cb)) {
 122                 ca++;
 123                 cb++;
 124                 m += 8;
 125                 n--;
 126         }
 127         /* Now count matching bits. */
 128         if (n) {
 129                 n = 0x80;
 130                 while (n && ((*ca & n) == (*cb & n))) {
 131                         m++;
 132                         n >>= 1;
 133                 }
 134         }
 135         return (m);
 136 }
 137
 138 /*
 139  * Local Variables:
 140  * tab-width: 4
 141  * c-indent-level: 4
 142  * c-argdecl-indent: 4
 143  * c-continued-statement-offset: 4
 144  * c-continued-brace-offset: -4
 145  * c-label-offset: -4
 146  * c-brace-offset: 0
 147  * End:
 148  */