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#define __FORCE_GLIBC

#include <features.h>

#include <stdio.h>

#include <string.h>

#include <errno.h>

#include <sys/param.h>

#include <netinet/in.h>

#include <netdb.h>

#include <fcntl.h>

#include <unistd.h>

#define HOSTID "/etc/hostid"

int sethostid(long int new_id)

{

        int fd;

        int ret;

        if (geteuid() || getuid()) return __set_errno(EPERM);

        if ((fd=open(HOSTID,O_CREAT|O_WRONLY,0644))<0) return -1;

        ret = write(fd,(void *)&new_id,sizeof(new_id)) == sizeof(new_id)

                ? 0 : -1;

        close (fd);

        return ret;

}

long int gethostid(void)

{

        char host[MAXHOSTNAMELEN + 1];

        int fd, id;

        /* If hostid was already set the we can return that value.

         * It is not an error if we cannot read this file. It is not even an

         * error if we cannot read all the bytes, we just carry on trying...

         */

        if ((fd=open(HOSTID,O_RDONLY))>=0 && read(fd,(void *)&id,sizeof(id)))

        {

                close (fd);

                return id;

        }

        if (fd >= 0) close (fd);

        /* Try some methods of returning a unique 32 bit id. Clearly IP

         * numbers, if on the internet, will have a unique address. If they

         * are not on the internet then we can return 0 which means they should

         * really set this number via a sethostid() call. If their hostname

         * returns the loopback number (i.e. if they have put their hostname

         * in the /etc/hosts file with 127.0.0.1) then all such hosts will

         * have a non-unique hostid, but it doesn't matter anyway and

         * gethostid() will return a non zero number without the need for

         * setting one anyway.

         *                                              Mitch

         */

        if (gethostname(host,MAXHOSTNAMELEN)>=0 && *host) {

                struct hostent *hp;

                struct in_addr in;

                if ((hp = gethostbyname(host)) == (struct hostent *)NULL)

                /* This is not a error if we get here, as all it means is that

                 * this host is not on a network and/or they have not

                 * configured their network properly. So we return the unset

                 * hostid which should be 0, meaning that they should set it !!

                 */

                        return 0;

                else {

                        memcpy((char *) &in, (char *) hp->h_addr, hp->h_length);

                        /* Just so it doesn't look exactly like the IP addr */

                        return(in.s_addr<<16|in.s_addr>>16);

                }

        }

        else return 0;

}