shmtool.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#define SEGSIZE 100
main (int argc, char *argv[])
{
  key_t key;
  int shmid, cntr;
  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)) == -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 ();
    }
}

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

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

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

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", &myshmds.shm_perm.mode);
  /* Update the mode */
  shmctl (shmid, IPC_SET, &myshmds);
  printf ("New permissions are : %o\n", myshmds.shm_perm.mode);
}

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);
}