/*
 * semopup.c
 * Increments a semaphore.
 */

#include <stdio.h>
#include <sys/sem.h>
#include <sys/ipc.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
	key_t key;
	struct sembuf sops[1];
	int semid;

	if(argc!=2)
	{
		fprintf(stdout,"usage: %s <value to increment semaphore>\n",argv[0]);
		fflush(stdout);
		return -1;
	}

	sops[0].sem_num=0;
	sops[0].sem_op=atoi(argv[1]);
	sops[0].sem_flg=0;

	if(sops[0].sem_op<=0)
	{
		fprintf(stdout,"please enter a positive # to increment the semaphore by\n");
		fflush(stdout);
		return -1;
	}

	if((key=ftok("semfile",'a'))==-1)
	{
		fprintf(stdout,"failed to get key %s\n",strerror(errno));
		fflush(stdout);
		return -1;
	}

	fprintf(stdout,"%x \n",key);

	if((semid=semget(key,1,S_IRUSR | S_IWUSR))==-1)				/* get the semaphore */
	{
		fprintf(stdout,"semget failed %s\n",strerror(errno));
		fflush(stdout);
		return -1;
	}

	if(semop(semid,sops,1)!=0)						/* incrememnt the semaphore */
	{
		fprintf(stdout,"semop failed %s\n",strerror(errno));
		fflush(stdout);
		return -1;
	}

	fprintf(stdout,"semaphore incremented by %d\n",sops[0].sem_op);
	fflush(stdout);

	return 0;
}