svshm/svshm_xfr.h

This is svshm/svshm_xfr.h (Listing 48-1, page 1002), an example from the book, The Linux Programming Interface.

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/*  svshm_xfr.h

   Header file used by the svshm_xfr_reader.c and svshm_xfr_writer.c programs.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include "binary_sems.h"        /* Declares our binary semaphore functions */
#include "tlpi_hdr.h"

/* Hard-coded keys for IPC objects */

#define SHM_KEY 0x1234          /* Key for shared memory segment */
#define SEM_KEY 0x5678          /* Key for semaphore set */

#define OBJ_PERMS (S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP)
                                /* Permissions for our IPC objects */

/* Two semaphores are used to ensure exclusive, alternating access
   to the shared memory segment */

#define WRITE_SEM 0             /* Writer has access to shared memory */
#define READ_SEM 1              /* Reader has access to shared memory */

#ifndef BUF_SIZE                /* Allow "cc -D" to override definition */
#define BUF_SIZE 1024           /* Size of transfer buffer */
#endif

struct shmseg {                 /* Defines structure of shared memory segment */
    int cnt;                    /* Number of bytes used in 'buf' */
    char buf[BUF_SIZE];         /* Data being transferred */
};

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