uulock -- HDB style tty locking [mi.misc]

[Jon Zeeff]

Archive-name: uulock
Original-posting-by: zeeff at b-tech.ann-arbor.mi.us (Jon Zeeff)
Original-subject:  KA9Q questions
Reposted-by: emv at math.lsa.umich.edu (Edward Vielmetti)

[This is an experimental alt.sources re-posting from the newsgroup(s)
mi.misc. Comments on this service to emv at math.lsa.umich.edu 
(Edward Vielmetti).]


>(Anyone tried to implement locking so uucp doesn't get upset?)

Here is something I wrote for HDB uucp.  Could probably be easily 
modified for others.  

/*

  Lock a tty and then run a program.  Blow away old locks.

  Written for Sys V with HDB style locks.
  Written by Jon Zeeff (zeeff at b-tech.ann-arbor.mi.us)
  This program placed in the public domain.

*/

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>
#include <fcntl.h>
#include <termio.h>
#include <sys/errno.h>

char *strcpy();
char *strcat();
unsigned sleep();
unsigned alarm();
void exit();
int pid;

FILE *lock;
char tty_lock[100];

main(argc,argv)
int argc;
char **argv;
{

        if (argc < 3) {
           fprintf(stderr,"Usage: uulock tty command args\n");
           exit(1);
        }
 
	/* create a hdb style lock file */

        strcpy(tty_lock,"/usr/spool/locks/LCK..");
        strcat(tty_lock,argv[1]);

        check_lock(tty_lock);
        umask(022);

	lock = fopen(tty_lock,"w");
	if (lock) {
		fprintf(lock,"%10.10d\n",(int)getpid());
		fclose(lock);

                if (pid = fork()) {
		  int w;
                  while ((w = wait((int *)0)) != pid && w != -1);
                  unlink(tty_lock);
                } else {
                   execvp(argv[2],&argv[2]);
		   printf("Can't exec that program\n");
		   exit(2);
                } 
	} else {
          fprintf(stderr,"tty port in use\n");
          return 2;
        }

   return 0;
}

/* remove a lock file if the process is no longer there */

check_lock(file_name)
char *file_name;
{

	int fd;
        char lock_pid[11];
	extern int errno;

	if ((fd = open(file_name, O_RDONLY)) == -1) {
           unlink(file_name);
           return 0;
        }

	read(fd,lock_pid, 10);
	close(fd);

	if ((kill(atoi(lock_pid), 0)) == 0 || errno == EPERM) 
           return 1;    /* process is active */

        unlink(file_name);
        return 0;
}
-- 
Jon Zeeff    	zeeff at b-tech.ann-arbor.mi.us  or b-tech!zeeff