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 /*
  43  * Return a pointer to the interface struct for the passed address.
  44  *
  45  * s      socket file descriptor
  46  * addrp  destination address on interface
  47  */
  48 struct ifreq *
  49 getif(int s, struct in_addr *addrp)
  50 {
  51         int maxmatch;
  52         int len, m, incr;
  53         struct ifreq *ifrq, *ifrmax;
  54         struct sockaddr_in *sip;
  55         char *p;
  56
  57         /* If no address was supplied, just return NULL. */
  58         if (!addrp)
  59                 return NULL;
  60
  61         /* Get the interface config if not done already. */
  62         if (ifconf.ifc_len == 0) {
  63 #ifdef  SVR4
  64                 /*
  65                  * SysVr4 returns garbage if you do this the obvious way!
  66                  * This one took a while to figure out... -gwr
  67                  */
  68                 struct strioctl ioc;
  69                 ioc.ic_cmd = SIOCGIFCONF;
  70                 ioc.ic_timout = 0;
  71                 ioc.ic_len = sizeof(ifreq);
  72                 ioc.ic_dp = (char *) ifreq;
  73                 m = ioctl(s, I_STR, (char *) &ioc);
  74                 ifconf.ifc_len = ioc.ic_len;
  75                 ifconf.ifc_req = ifreq;
  76 #else   /* SVR4 */
  77                 ifconf.ifc_len = sizeof(ifreq);
  78                 ifconf.ifc_req = ifreq;
  79                 m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
  80 #endif  /* SVR4 */
  81                 if ((m < 0) || (ifconf.ifc_len <= 0)) {
  82                         report(LOG_ERR, "ioctl SIOCGIFCONF");
  83                         return NULL;
  84                 }
  85         }
  86         maxmatch = 7;                           /* this many bits or less... */
  87         ifrmax = NULL;                          /* ... is not a valid match  */
  88         p = (char *) ifreq;
  89         len = ifconf.ifc_len;
  90         while (len > 0) {
  91                 ifrq = (struct ifreq *) p;
  92                 sip = (struct sockaddr_in *) &ifrq->ifr_addr;
  93                 m = nmatch(addrp, &(sip->sin_addr));
  94                 if (m > maxmatch) {
  95                         maxmatch = m;
  96                         ifrmax = ifrq;
  97                 }
  98 #ifndef IFNAMSIZ
  99                 /* BSD not defined or earlier than 4.3 */
 100                 incr = sizeof(*ifrq);
 101 #else
 102                 incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
 103 #endif
 104
 105                 p += incr;
 106                 len -= incr;
 107         }
 108
 109         return ifrmax;
 110 }
 111
 112 /*
 113  * Return the number of leading bits matching in the
 114  * internet addresses supplied.
 115  *
 116  * ca, cb  ptrs to IP address, network order
 117  */
 118 static int
 119 nmatch(u_char *ca, u_char *cb)
 120 {
 121         u_int m = 0;                            /* count of matching bits */
 122         u_int n = 4;                            /* bytes left, then bitmask */
 123
 124         /* Count matching bytes. */
 125         while (n && (*ca == *cb)) {
 126                 ca++;
 127                 cb++;
 128                 m += 8;
 129                 n--;
 130         }
 131         /* Now count matching bits. */
 132         if (n) {
 133                 n = 0x80;
 134                 while (n && ((*ca & n) == (*cb & n))) {
 135                         m++;
 136                         n >>= 1;
 137                 }
 138         }
 139         return (m);
 140 }
 141
 142 /*
 143  * Local Variables:
 144  * tab-width: 4
 145  * c-indent-level: 4
 146  * c-argdecl-indent: 4
 147  * c-continued-statement-offset: 4
 148  * c-continued-brace-offset: -4
 149  * c-label-offset: -4
 150  * c-brace-offset: 0
 151  * End:
 152  */