/*
 * Project 3 - Shared memory and semaphores.
 * Dr. Silaghi's Operating System Concepts.
 * memory.c - Common shared memory functions are in here.
 * By Michael Rywalt - 2569
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <syslog.h>
#include <unistd.h>
#include "common.h"

/* Reserve enough memory for the integer used to count. */
#define SHM_SIZE (sizeof(int))

/********************
 * InitSharedMemory *
 ********************
 *
 * Function: InitSharedMemory
 *
 * Purpose: Initializes the shared memory segment.
 *
 * 	Note: It is up to the caller to (re)initialize this memory.
 *
 * Parameters: None.
 *
 * Returns: Pointer to the shared memory segment.
 */
void *InitSharedMemory()
{
	int iShmid;
	char *pcData;
	key_t key;

	syslog(LOG_INFO, " [%s] Initializing shared memory...", __FUNCTION__);

	/* Get the key. */
	if((key = ftok(PROJECT_KEY, PROJECT_ID)) == -1)
	{
		syslog(LOG_INFO, " [%s] Error getting key.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Create the shared memory segment. */
	if((iShmid = shmget(key, SHM_SIZE, IPC_CREAT | 0644)) < 0)
	{
		syslog(LOG_INFO, " [%s] Error creating shared memory segment.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	/* Make the data segment accessible. */
	if((pcData = shmat(iShmid, NULL, 0)) == (char*) -1)
	{
		syslog(LOG_INFO, " [%s] Error activating shared memory segment.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	return pcData;
}

/**********************
 * DetachSharedMemory *
 **********************
 *
 * Function: DetatchSharedMemory
 *
 * Purpose: Detatches from shared memory segment.
 *
 * Parameters:	pMemory		- Pointer to memory semgment.
 *
 * Returns: Nothing.
 */
void DetatchSharedMemory(void *pMemory)
{

        int iShmid;
        key_t key;
	struct shmid_ds shm_ds;

        syslog(LOG_INFO, " [%s] Uninitializing shared memory.", __FUNCTION__);

        /* Get the key. */
        if((key = ftok(PROJECT_KEY, PROJECT_ID)) == -1)
        {
                syslog(LOG_INFO, " [%s] Error getting key.", __FUNCTION__);
                EXIT(EXIT_ERROR);
        }

        /* Get the shared memory segment. */
        if((iShmid = shmget(key, SHM_SIZE, IPC_CREAT | 0644)) < 0)
        {
                syslog(LOG_INFO, " [%s] Error creating shared memory segment.", __FUNCTION__);
                EXIT(EXIT_ERROR);
        }

	if((shmctl(iShmid, IPC_RMID, &shm_ds)) < 0)
	{
		syslog(LOG_INFO, " [%s] Error removing shared memory.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	if(shmdt(pMemory) == -1)
	{
		syslog(LOG_INFO, " [%s] Error destroying shared memory segment.", __FUNCTION__);
		EXIT(EXIT_ERROR);
	}

	if(pMemory)
	{
		pMemory = NULL;
	}
}