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/*
* getif.c : get an interface structure
*
* $Id: getif.c,v 1.3 1996/09/22 21:52:12 wosch Exp $
*/
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#if defined(SUNOS) || defined(SVR4)
#include <sys/sockio.h>
#endif
#ifdef SVR4
#include <sys/stropts.h>
#endif
#include <sys/time.h> /* for struct timeval in net/if.h */
#include <net/if.h> /* for struct ifreq */
#include <netinet/in.h>
#ifndef NO_UNISTD
#include <unistd.h>
#endif
#include <syslog.h>
#include <errno.h>
#include <assert.h>
#include "getif.h"
#include "report.h"
#ifdef __bsdi__
#define BSD 43
#endif
static struct ifreq ifreq[10]; /* Holds interface configuration */
static struct ifconf ifconf; /* points to ifreq */
static int nmatch();
/* Return a pointer to the interface struct for the passed address. */
struct ifreq *
getif(s, addrp)
int s; /* socket file descriptor */
struct in_addr *addrp; /* destination address on interface */
{
int maxmatch;
int len, m, incr;
struct ifreq *ifrq, *ifrmax;
struct sockaddr_in *sip;
char *p;
/* If no address was supplied, just return NULL. */
if (!addrp)
return (struct ifreq *) 0;
/* Get the interface config if not done already. */
if (ifconf.ifc_len == 0) {
#ifdef SVR4
/*
* SysVr4 returns garbage if you do this the obvious way!
* This one took a while to figure out... -gwr
*/
struct strioctl ioc;
ioc.ic_cmd = SIOCGIFCONF;
ioc.ic_timout = 0;
ioc.ic_len = sizeof(ifreq);
ioc.ic_dp = (char *) ifreq;
m = ioctl(s, I_STR, (char *) &ioc);
ifconf.ifc_len = ioc.ic_len;
ifconf.ifc_req = ifreq;
#else /* SVR4 */
ifconf.ifc_len = sizeof(ifreq);
ifconf.ifc_req = ifreq;
m = ioctl(s, SIOCGIFCONF, (caddr_t) & ifconf);
#endif /* SVR4 */
if ((m < 0) || (ifconf.ifc_len <= 0)) {
report(LOG_ERR, "ioctl SIOCGIFCONF");
return (struct ifreq *) 0;
}
}
maxmatch = 7; /* this many bits or less... */
ifrmax = (struct ifreq *) 0;/* ... is not a valid match */
p = (char *) ifreq;
len = ifconf.ifc_len;
while (len > 0) {
ifrq = (struct ifreq *) p;
sip = (struct sockaddr_in *) &ifrq->ifr_addr;
m = nmatch(addrp, &(sip->sin_addr));
if (m > maxmatch) {
maxmatch = m;
ifrmax = ifrq;
}
#ifndef IFNAMSIZ
/* BSD not defined or earlier than 4.3 */
incr = sizeof(*ifrq);
#else
incr = ifrq->ifr_addr.sa_len + IFNAMSIZ;
#endif
p += incr;
len -= incr;
}
return ifrmax;
}
/*
* Return the number of leading bits matching in the
* internet addresses supplied.
*/
static int
nmatch(ca, cb)
u_char *ca, *cb; /* ptrs to IP address, network order */
{
u_int m = 0; /* count of matching bits */
u_int n = 4; /* bytes left, then bitmask */
/* Count matching bytes. */
while (n && (*ca == *cb)) {
ca++;
cb++;
m += 8;
n--;
}
/* Now count matching bits. */
if (n) {
n = 0x80;
while (n && ((*ca & n) == (*cb & n))) {
m++;
n >>= 1;
}
}
return (m);
}
/*
* Local Variables:
* tab-width: 4
* c-indent-level: 4
* c-argdecl-indent: 4
* c-continued-statement-offset: 4
* c-continued-brace-offset: -4
* c-label-offset: -4
* c-brace-offset: 0
* End:
*/
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