//
//    shared.cpp - a shared memory manager for passing messages
//
//    Copyright (C) 2000 by Hugh Jack <jackh@gvsu.edu>
//
//    This program is free software; you can redistribute it and/or modify
//    it under the terms of the GNU General Public License as published by
//    the Free Software Foundation; either version 2 of the License, or
//    (at your option) any later version.
//
//    This program is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU General Public License for more details.
//
//    You should have received a copy of the GNU General Public License
//    along with this program; if not, write to the Free Software
//    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
//


#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <ctype.h>

#include "shared.h"



#define SEGSIZE 100


void writeshm(int, char *, char *);
void readshm(int, char *);
void removeshm(int);
void changemode(int, char *);
void usage();


int main(int argc, char *argv[]){
        key_t key;
        int   shmid;
        char  *segptr;

        if(argc == 1) usage();
        /* Create unique key via call to ftok() */
        key = ftok(".", 'S');
        /* Open the shared memory segment - create if necessary */
        if((shmid = shmget(key, SEGSIZE, IPC_CREAT|IPC_EXCL|0666)) == -1){
                printf("Shared memory segment exists - opening as client\n");
                /* Segment probably already exists - try as a client */
                if((shmid = shmget(key, 0, 0)) == -1){
                        perror("shmget");
                        exit(1);
                }
        } else {
                printf("Creating new shared memory segment\n");
        }
        /* Attach (map) the shared memory segment into the current process */
        if((segptr = (char *)shmat(shmid, 0, 0)) == NULL){
                perror("shmat");
                exit(1);
        }
        
        switch(tolower(argv[1][0])){
                case 'w': writeshm(shmid, segptr, argv[2]);
                          break;
                case 'r': readshm(shmid, segptr);
                          break;
                case 'd': removeshm(shmid);
                          break;
                case 'm': changemode(shmid, argv[2]);
                          break;
                 default: usage();
        }
}

void writeshm(int shmid, char *segptr, char *text){
        strcpy(segptr, text);
        printf("Done...\n");
}

void readshm(int shmid, char *segptr){
        printf("segptr: %s\n", segptr);
}

void removeshm(int shmid){
        shmctl(shmid, IPC_RMID, 0);
        printf("Shared memory segment marked for deletion\n");
}

void changemode(int shmid, char *mode) {
        struct shmid_ds myshmds;

        /* Get current values for internal data structure */
        shmctl(shmid, IPC_STAT, &myshmds);
        /* Display old permissions */
        printf("Old permissions were: %o\n", myshmds.shm_perm.mode);
        /* Convert and load the mode */ 
        sscanf(mode, "%o", (unsigned*)&myshmds.shm_perm.mode);
        /* Update the mode */
        shmctl(shmid, IPC_SET, &myshmds);
        printf("New permissions are : %o\n", myshmds.shm_perm.mode);
}

void usage(){
        fprintf(stderr, "shmtool - A utility for tinkering with shared memory\n");
        fprintf(stderr, "\nUSAGE:  shmtool (w)rite <text>\n");
        fprintf(stderr, "                (r)ead\n");
        fprintf(stderr, "                (d)elete\n");
        fprintf(stderr, "                (m)ode change <octal mode>\n");
        exit(1);
}