//    alloc_data_area.C


#include "common.h"
#include "message.h"

#include <string.h>
#include <stdio.h>

#include <stdlib.h> /* getenv, exit */
#include <errno.h>

#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <fcntl.h>

#ifdef __cplusplus
extern "C" {
#endif
    int shm_open(const char *, int, mode_t);
#ifdef __cplusplus
}
#endif

//    only POSIX option is supported for Linux systems which DO support the real time POSIX 4 options


#include <sys/stat.h>


void * alloc_data_area(int id, int size)
{
   char object_name[16];

   size_t shmsize;               // segment size in bytes
   int shmid;

   void * shmaddress;
   int shmkey;
#ifdef MASTER
   int i;
#endif

//    obtain shared memory ID - this will create segment if needed
//    In practice only the MASTER task which starts first will ever create and initialise

    shmkey = id;
    shmsize = size;

//    create a file mapped object (MASTER) or obtain ID of existing object

    sprintf(object_name,"/SHM_%d", shmkey);

#ifdef MASTER
    shmid = shm_open(object_name, O_RDWR|O_CREAT, (mode_t) -1);
#else
    shmid = shm_open(object_name, O_RDWR, (mode_t) -1);
#endif
    if (shmid == -1)  {
             ReportError();
             sprintf(message_buffer, "shm_open failed - This must be fixed - exiting.");
             report_message(MSG_FAILURE);
             exit(1);
    }

#ifdef MASTER
        sprintf(message_buffer, "File mapped object %s of size %lu created", object_name, (unsigned long int)shmsize);
#else
        sprintf(message_buffer, "File mapped object %s accessed", object_name);
#endif

    report_message(MSG_INFORMATION);

#ifdef MASTER

//    size the memory object

    i = ftruncate(shmid, shmsize);
    if (i == -1)  {
             ReportError();
             sprintf(message_buffer, "ftruncate failed - This must be fixed - exiting.");
             report_message(MSG_FAILURE);
             exit(1);
    }
#endif

//    attach the memory segment

    sprintf(message_buffer, "Memory mapping %lu bytes", (unsigned long int)shmsize);
    report_message(MSG_INFORMATION);
    shmaddress = mmap((caddr_t) NULL, (size_t) shmsize, PROT_READ|PROT_WRITE, MAP_SHARED, shmid, (off_t) 0);
    if (shmaddress == (void *) MAP_FAILED) {
        ReportError();
        sprintf(message_buffer, "mmap failed - This must be fixed - exiting.");
        report_message(MSG_FAILURE);
        exit(1);
    }

//    tidy up 

    close(shmid);

    sprintf(message_buffer, "Shared memory segment located at address %p.", shmaddress);
    report_message(MSG_INFORMATION);
    
    return shmaddress;

}