svmsg/svmsg_create.c

This is svmsg/svmsg_create.c (Listing 46-1, page 938), an example from the book, The Linux Programming Interface.

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

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/* svmsg_create.c

   Experiment with the use of msgget() to create a System V message queue.
*/
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/stat.h>
#include "tlpi_hdr.h"
static void             /* Print usage info, then exit */
usageError(const char *progName, const char *msg)
{
    if (msg != NULL)
        fprintf(stderr, "%s", msg);
    fprintf(stderr, "Usage: %s [-cx] {-f pathname | -k key | -p} "
                            "[octal-perms]\n", progName);
    fprintf(stderr, "    -c           Use IPC_CREAT flag\n");
    fprintf(stderr, "    -x           Use IPC_EXCL flag\n");
    fprintf(stderr, "    -f pathname  Generate key using ftok()\n");
    fprintf(stderr, "    -k key       Use 'key' as key\n");
    fprintf(stderr, "    -p           Use IPC_PRIVATE key\n");
    exit(EXIT_FAILURE);
}
int
main(int argc, char *argv[])
{
    int numKeyFlags;            /* Counts -f, -k, and -p options */
    int flags, msqid, opt;
    unsigned int perms;
    long lkey;
    key_t key;

    /* Parse command-line options and arguments */

    numKeyFlags = 0;
    flags = 0;

    while ((opt = getopt(argc, argv, "cf:k:px")) != -1) {
        switch (opt) {
        case 'c':
            flags |= IPC_CREAT;
            break;

        case 'f':               /* -f pathname */
            key = ftok(optarg, 1);
            if (key == -1)
                errExit("ftok");
            numKeyFlags++;
            break;

        case 'k':               /* -k key (octal, decimal or hexadecimal) */
            if (sscanf(optarg, "%li", &lkey) != 1)
                cmdLineErr("-k option requires a numeric argument\n");
            key = lkey;
            numKeyFlags++;
            break;

        case 'p':
            key = IPC_PRIVATE;
            numKeyFlags++;
            break;

        case 'x':
            flags |= IPC_EXCL;
            break;

        default:
            usageError(argv[0], "Bad option\n");
        }
    }

    if (numKeyFlags != 1)
        usageError(argv[0], "Exactly one of the options -f, -k, "
                            "or -p must be supplied\n");

    perms = (optind == argc) ? (S_IRUSR | S_IWUSR) :
                getInt(argv[optind], GN_BASE_8, "octal-perms");

    msqid = msgget(key, flags | perms);
    if (msqid == -1)
        errExit("msgget");

    printf("%d\n", msqid);
    exit(EXIT_SUCCESS);
}

 

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