pshm_write.c

/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2024.                   *
*                                                                         *
* This program is free software. You may use, modify, and redistribute it *
* under the terms of the GNU General Public License as published by the   *
* Free Software Foundation, either version 3 or (at your option) any      *
* later version. This program is distributed without any warranty.  See   *
* the file COPYING.gpl-v3 for details.                                    *
\*************************************************************************/

/* Listing 54-2 */

#include <fcntl.h>
#include <sys/mman.h>
#include "tlpi_hdr.h"

int
main(int argc, char *argv[])
{
    int fd;
    size_t len;                 /* Size of shared memory object */
    char *addr;

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s shm-name string\n", argv[0]);

    fd = shm_open(argv[1], O_RDWR, 0);      /* Open existing object */
    if (fd == -1)
        errExit("shm_open");

    len = strlen(argv[2]);
    if (ftruncate(fd, len) == -1)           /* Resize object to hold string */
        errExit("ftruncate");
    printf("Resized to %ld bytes\n", (long) len);

    addr = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED)
        errExit("mmap");

    if (close(fd) == -1)                    /* 'fd' is no longer needed */
        errExit("close");

    printf("copying %ld bytes\n", (long) len);
    memcpy(addr, argv[2], len);             /* Copy string to shared memory */
    exit(EXIT_SUCCESS);
}