test11_5.txt

linux under the C programming which complementary with the book of <linux under the C programming

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <stdio.h>

#define SEM_NUM 10
#define SEM_MODE (IPC_CREAT|0660)
void printf_stat(union semun *arg);

int main(void)
{
    	int semid;
	union semun semopts;
    	struct semid_ds semds;
    
	if ((semid=semget(IPC_PRIVATE, SEM_NUM, SEM_MODE))==-1)
	{
    		fprintf(stderr, "semget error!\n");
    		exit(1);
	}

	semopts.buf=&semds;
	if(semctl(semid,0,IPC_STAT,semopts)==-1)
	{
      		fprintf(stderr, "get semid_ds error!\n");
    		exit(1);
	}
	printfmode(&semopts);

	changemode(semid, 0600); 
	if(semctl(semid,0, IPC_STAT, semopts)==-1)
	{
      		fprintf(stderr, "get semid_ds error!\n");
    		exit(1);
	}
    	printfmode(&semopts);

	if(semctl(semid,0, IPC_RMID, 0)<0)
	{
      		fprintf(stderr,"semctl error\n");
    		exit(1);
	}
	exit(0);
}


void printfmode (union semun *arg)
{ 
    	printf("  mode=%d:\n", arg->buf->sem_perm.mode);     
	return;
}


void changemode(int sid, char *mode)
{
    	int rc;
    	union semun semopts;
  	struct semid_ds mysemds;

    	semopts.buf=&mysemds;
    	rc=semctl(sid,0,  IPC_STAT, semopts);

    	if(rc==-1)
    	{
        	printf("semctl error!\n");
        	exit(1);
    	}

    	sscanf(mode,"%ho", &semopts.buf->sem_perm.mode);
    	semctl(sid,0,  IPC_SET, semopts);

    	return;
}