/* Open and lock file until interupted.  Does not change file.*/
/* Usage: lock filename &
	  lockid=$!
	  exclusive use of file called named filename
          kill -HUP $lockid
*/
/*Started: RJ Botting, Sep 1999 SunOS ftp 4.1.3_U1 2 sun4m */
#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <signal.h>
#include <sys/file.h>
/*flock - apply or remove an advisory lock on an open file*/

int lockfd; /* file descriptor */

void unlock()
{
   int ans;
   ans=flock( lockfd, LOCK_UN);
   /*fprintf(stderr, "DBUG5: flock( lockfd, LOCK_UN) returns %d\n", ans);*/
   if(ans== -1)perror("");
   ans=close(lockfd);
   if(ans== -1)perror("");
   /*fprintf(stderr, "DBUG6: close returns %d\n", ans);*/
   exit(0);
}
main( argc, argv)
int argc; char *argv[];
{
   int fl; 
   if(argc!=2){
	fprintf(stderr, "Usage: %s filename.\n", argv[0]);
	exit(1);
   }
   /*fprintf(stderr, "DBUG1: %s %s\n",argv[0], argv[1]);*/
   lockfd=open(argv[1], O_RDONLY );
   if( -1 == lockfd){
	fprintf(stderr, "Open %s failed with errno %d.\n", argv[1], errno);
	perror("");
	exit(1);
   }

   /*fprintf(stderr, "DBUG2: %s %s about to flock\n",argv[0], argv[1]);*/

   fl= flock( lockfd, LOCK_EX);
   if(!fl ){
   /*fprintf(stderr, "DBUG3: flock returned %d, %s %s can access file\n",fl, argv[0], argv[1]);*/
   signal(SIGHUP, unlock);
   /*fprintf(stderr, "DBUG4: waiting to be HUPped\n");*/
	/*Goto sleep until signalled*/
	   while(1)sleep(1);
   }
   else{
    fprintf(stderr,
            "File locking (flock) returned %d with errno %d!\n", fl, errno
    );
    perror("");
   }
}