usr/src/new/nntp/server/subnet.c

#ifndef lint
static  char    *sccsid = "@(#)subnet.c 1.2     (Berkeley) 10/15/87";
#endif


#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include "../common/conf.h"

#ifdef SUBNET

/*
 * The following routines provide a general interface for
 * subnet support.  Like the library function "inet_netof",
 * which returns the standard (i.e., non-subnet) network
 * portion of an internet address, "inet_snetof" returns
 * the subnetwork portion -- if there is one.  If there
 * isn't, it returns 0.
 *
 * Subnets, under 4.3, are specific to a given set of
 * machines -- right down to the network interfaces.
 * Because of this, the function "getifconf" must be
 * called first.  This routine builds a table listing
 * all the (internet) interfaces present on a machine,
 * along with their subnet masks.  Then when inet_snetof
 * is called, it can quickly scan this table.
 *
 * Unfortunately, there "ain't no graceful way" to handle
 * certain situations.  For example, the kernel permits
 * arbitrary subnet bits -- that is, you could have a
 * 22 bit network field and a 10 bit subnet field.
 * However, due to braindamage at the user level, in
 * such sterling routines as getnetbyaddr, you need to
 * have a subnet mask which is an even multiple of 8.
 * Unless you are running with class C subnets, in which
 * case it should be a multiple of 4.  Because of this rot,
 * if you have non-multiples of 4 bits of subnet, you should
 * define DAMAGED_NETMASK when you compile.  This will round
 * things off to a multiple of 8 bits.
 *
 * And even that may not work.
 */

/*
 * One structure for each interface, containing
 * the network number and subnet mask, stored in HBO.
 */
struct in_if {
        u_long  i_net;          /* Network number, shifted right */
        u_long  i_subnetmask;   /* Subnet mask for this if */
        int     i_bitshift;     /* How many bits right for outside */
};

/*
 * Table (eventually, once we malloc) of
 * internet interface subnet informaiton.
 */
static  struct in_if    *in_ifsni;

static  int             if_count;

/*
 * Get the network interface configuration,
 * and squirrel away the network numbers and
 * subnet masks of each interface.  Return
 * number of interfaces found, or -1 on error.
 * N.B.: don't call this more than once...
 */

getifconf()
{
        register int    i, j;
        int             s;
        struct ifconf   ifc;
        char            buf[1024];
        register struct ifreq   *ifr;
        u_long          inet_netof();

        /*
         * Find out how many interfaces we have, and malloc
         * room for information about each one.
         */

        s = socket(AF_INET, SOCK_DGRAM, 0);
        if (s < 0)
                return (-1);

        ifc.ifc_buf = buf;
        ifc.ifc_len = sizeof (buf);

        if (ioctl(s, SIOCGIFCONF, &ifc) < 0) {
                (void) close(s);
                return (-1);
        }

        /*
         * if_count here is the count of possible
         * interfaces we may be interested in... actual
         * interfaces may be less (some may not be internet,
         * not all are necessarily up, etc.)
         */

        if_count = ifc.ifc_len / sizeof (struct ifreq);

        in_ifsni = (struct in_if *) malloc(if_count * sizeof (struct in_if));
        if (in_ifsni == 0) {
                (void) close(s);
                return (-1);
        }

        for (i = j = 0; i < if_count; ++i) {
                ifr = &ifc.ifc_req[i];
                if (ioctl(s, SIOCGIFFLAGS, ifr) < 0)
                        continue;
                if ((ifr->ifr_flags & IFF_UP) == 0)
                        continue;
                if (ioctl(s, SIOCGIFADDR, ifr) < 0)
                        continue;
                if (ifr->ifr_addr.sa_family != AF_INET)
                        continue;
                in_ifsni[j].i_net =
                   inet_netof((*(struct sockaddr_in *)&ifr->ifr_addr).sin_addr);
                if (ioctl(s, SIOCGIFNETMASK, ifr) < 0)
                        continue;
                in_ifsni[j].i_subnetmask =
                 ntohl((*(struct sockaddr_in *)&ifr->ifr_addr).sin_addr.s_addr);
                /*
                 * The following should "never happen".  But under SunOs
                 * 3.4, along with the rest of their broken networking code,
                 * SIOCGIFNETMASK can get a netmask which is 0.  There
                 * really isn't anything that "right" that we can do
                 * about it, so we'll set their subnet mask to be a class
                 * B subnet.  Which may or may not be right.
                 */
                if (in_ifsni[j].i_subnetmask == 0)
                        in_ifsni[j].i_subnetmask = IN_CLASSB_NET;
                in_ifsni[j].i_bitshift = bsr(in_ifsni[j].i_subnetmask);
                j++;
        }

        if_count = j;

        (void) close(s);

        return (if_count);
}


/*
 * Return the (sub)network number from an internet address.
 * "in" is in NBO, return value in host byte order.
 * If "in" is not a subnet, return 0.
 */

u_long
inet_snetof(in)
        u_long  in;
{
        register int    j;
        register u_long i = ntohl(in);
        register u_long net;
        u_long          inet_netof(), inet_lnaof();

        net = inet_netof(in);

        /*
         * Check whether network is a subnet;
         * if so, return subnet number.
         */
        for (j = 0; j < if_count; ++j)
                if (net == in_ifsni[j].i_net) {
                        net = i & in_ifsni[j].i_subnetmask;
                        if (inet_lnaof(htonl(net)) == 0)
                                return (0);
                        else
                                return (net >> in_ifsni[j].i_bitshift);
                }

        return (0);
}


/*
 * Return the number of bits required to
 * shift right a mask into a getnetent-able entitity.
 */

bsr(mask)
        register int    mask;
{
        register int    count = 0;

        if (mask == 0)          /* "never happen", except with SunOs 3.4 */
                return (0);

        while ((mask & 1) == 0) {
                ++count;
                mask >>= 1;
        }
#ifdef DAMAGED_NETMASK
        count /= 8;                     /* XXX gag retch puke barf */
        count *= 8;
#endif
        return (count);
}

#endif