/*************************************************************************\
*                  Copyright (C) Michael Kerrisk, 2026.                   *
*                                                                         *
* 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.                                    *
\*************************************************************************/

/* pshm_read.c

   Usage: pshm_read shm-name

   Copy the contents of the POSIX shared memory object named in
   'name' to stdout.

   See also pshm_write.c.
*/
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include "tlpi_hdr.h"

int
main(int argc, char *argv[])
{
    int fd;
    char *addr;
    struct stat sb;

    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s shm-name\n", argv[0]);

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

    /* Use shared memory object size as length argument for mmap()
       and as number of bytes to write() */

    if (fstat(fd, &sb) == -1)
        errExit("fstat");

    addr = mmap(NULL, sb.st_size, PROT_READ, MAP_SHARED, fd, 0);
    if (addr == MAP_FAILED)
        errExit("mmap");

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

    write(STDOUT_FILENO, addr, sb.st_size);
    write(STDOUT_FILENO, "\n", 1);
    exit(EXIT_SUCCESS);
}