/*****************************************************************************
 Excerpt from "Linux Programmer's Guide - Chapter 6"
 (C)opyright 1994-1995, Scott Burkett
 ***************************************************************************** 
 MODULE: shmtool.c
 *****************************************************************************
 A command line tool for tinkering with SysV style Shared Memory Segments
 *****************************************************************************/

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

#define SEGSIZE	100

void writeshm(int shmid, char *segptr, char *text);
void readshm(int shmid, char *segptr);
void removeshm(int shmid);
void changemode(int shmid, char *mode);
void usage(void);



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, SEGSIZE, 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 = shmat(shmid, 0, 0)) == (char *)-1)
	{
		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();

	}

	return(0);
}

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, "%ho", &myshmds.shm_perm.mode);

	/* Update the mode */
	shmctl(shmid, IPC_SET, &myshmds);

	printf("New permissions are : %o\n", myshmds.shm_perm.mode);
}

void usage(void)
{
	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);
}