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/** \file server/drivers/lcd_sem.c
* semaphore code to mediate access to the parallel port.
*/
/*
* lcd_sem.c -- semaphore code written for lcdtime and meter to mediate
* access to the parallel port.
*
* Written by Benjamin Tse (blt@mundil.cs.mu.edu.au); August,October 1995
*
* Functions in this file:
* getkey returns the key for the semaphore
* sem_get create the semaphore (and initialise) if one doesn't exist
* otherwise return its key
* sem_wait wait on the semaphore
* sem_signal signal on the semaphore
* sem_remove remove the semaphore
*
* Legal stuff: At no stage was this program written, assembled or compiled on
* any computer at the University of Melbourne, Australia. This program is
* Copyright (C) 1995 Benjamin Tse (blt@mundil.cs.mu.oz.au) and covered by
* GNU's GPL. In particular, this program is free software and comes WITHOUT
* ANY WARRANTY.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h> /* for semaphore functions */
#include <sys/ipc.h>
#include <sys/sem.h>
#include <errno.h>
#ifdef HAVE_CONFIG_H
# include "config.h"
#endif
#include "lcd_sem.h"
// according to X/OPEN we have to define it ourselves
#ifndef HAVE_UNION_SEMUN
union semun {
int val; /* value for SETVAL */
struct semid_ds *buf; /* buffer for IPC_STAT, IPC_SET */
unsigned short int *array; /* array for GETALL, SETALL */
struct seminfo *__buf; /* buffer for IPC_INFO */
};
#endif
#define SEMAPHORE "portctrl"
#define SEMKEY 0x706f7274 /* semaphore key */
#define SEMCOUNT 1 /* number of semaphores to create */
#define WMODE 0660 /* access permissions */
#define SEM_SIGNAL 0,1,SEM_UNDO
#define SEM_WAIT 0,-1,SEM_UNDO
/* functions local to this file */
static key_t getkey(register char *p);
/* global variables */
static struct sembuf semaphore_wait = { SEM_WAIT };
static struct sembuf semaphore_signal = { SEM_SIGNAL };
/**
* Return the key for the semaphore.
*/
static key_t
getkey(register char *p)
{
return((key_t) SEMKEY);
}
/**
* Get semaphore.
* If the semaphore does not exist, create it and initialise it to 1,
* otherwise simply return the semaphore ID.
* \return Semaphore ID on success; terminate program with code \c 1 on error.
*/
int
sem_get(void)
{
int semid;
union semun semval;
if ((semid = semget(getkey(SEMAPHORE), SEMCOUNT, IPC_CREAT | IPC_EXCL | WMODE)) < 0) {
switch (errno) {
case EEXIST:
/* semaphore set exists, get id and return it */
if ((semid = semget(getkey(SEMAPHORE), SEMCOUNT, IPC_EXCL | WMODE)) < 0) {
perror("semget");
exit(1);
}
return semid;
break;
case EACCES:
/* don't have permissions for semaphore, need to change key */
perror("semget, can't get permissions for semaphore");
exit(1);
break;
default:
perror("semget");
exit(1);
break;
}
} else {
/* initialise semaphore to 1 */
semval.val = 1;
if (semctl(semid, 0, SETVAL, semval) < 0) {
perror("setval, can't initialise semaphore");
exit(1);
}
}
return semid;
}
/**
* Wait on the semaphore.
* \param sid Semaphore ID.
* \return \c 0 on success; terminate program with code \c 1 on error.
*/
int
sem_wait(int sid)
{
if (semop(sid, &semaphore_wait, 1) < -1) {
perror(SEMAPHORE);
exit(1);
}
return 0;
}
/**
* Signal on the semaphore.
* \param sid Semaphore ID.
* \return \c 0 on success; terminate program with code \c 1 on error.
*/
int
sem_signal(int sid)
{
if (semop(sid, &semaphore_signal, 1) < -1) {
perror(SEMAPHORE);
exit(1);
}
return 0;
}
/**
* Remove the semaphore
* \param sid Semaphore ID.
* \return \c 0 on success; terminate program with code \c 1 on error.
*/
int
sem_remove(int sid)
{
#ifdef EIDRM
int i;
union semun dummy;
if ((i = semctl(sid, 0, IPC_RMID, dummy)) < 0) {
switch (i) {
case EIDRM:
/* semaphore removed */
return 0;
break;
default:
perror("semctl, removing semaphore");
exit(1);
}
}
#endif
return 0;
}
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