svshm/svshm_mon.c

This is svshm/svshm_mon.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is the solution to Exercise 48-4 (page 1016).

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

 

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  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* svshm_mon.c

   Display information from the associated data structure for the
   System V shared memory segment identified on the command line.
*/
#include <sys/types.h>
#include <sys/shm.h>
#include <time.h>
#include "tlpi_hdr.h"
static void
printShmDS(const struct shmid_ds *ds)
{
    printf("Size:                      %ld\n", (long) ds->shm_segsz);
    printf("# of attached processes:   %ld\n", (long) ds->shm_nattch);

    printf("Mode:                      %lo",
            (unsigned long) ds->shm_perm.mode);
#ifdef SHM_DEST
    printf("%s", (ds->shm_perm.mode & SHM_DEST) ? " [DEST]" : "");
#endif
#ifdef SHM_LOCKED
    printf("%s", (ds->shm_perm.mode & SHM_LOCKED) ? " [LOCKED]" : "");
#endif
    printf("\n");

    printf("Last shmat():              %s", ctime(&ds->shm_atime));
    printf("Last shmdt():              %s", ctime(&ds->shm_dtime));
    printf("Last change:               %s", ctime(&ds->shm_ctime));

    printf("Creator PID:               %ld\n", (long) ds->shm_cpid);
    printf("PID of last attach/detach: %ld\n", (long) ds->shm_lpid);
}
int
main(int argc, char *argv[])
{
    if (argc != 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s shmid\n", argv[0]);

    struct shmid_ds ds;
    if (shmctl(getInt(argv[1], 0, "shmid"), IPC_STAT, &ds) == -1)
        errExit("shmctl");

    printShmDS(&ds);

    exit(EXIT_SUCCESS);
}

 

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Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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