svmsg/svmsg_ls.c

This is svmsg/svmsg_ls.c (Listing 46-6, page 953), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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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.

  Cover of The Linux Programming Interface
+/* svmsg_ls.c
+
+   Display a list of all System V message queues on the system.
+
+   This program is Linux-specific.
+*/
 #define _GNU_SOURCE
 #include <sys/types.h>
 #include <sys/msg.h>
 #include "tlpi_hdr.h"
 
 int
 main(int argc, char *argv[])
 {
     int maxind, ind, msqid;
     struct msqid_ds ds;
     struct msginfo msginfo;
 
     /* Obtain size of kernel 'entries' array */
 
     maxind = msgctl(0, MSG_INFO, (struct msqid_ds *) &msginfo);
     if (maxind == -1)
         errExit("msgctl-MSG_INFO");
 
     printf("maxind: %d\n\n", maxind);
     printf("index     id       key      messages\n");
 
     /* Retrieve and display information from each element of 'entries' array */
 
     for (ind = 0; ind <= maxind; ind++) {
         msqid = msgctl(ind, MSG_STAT, &ds);
         if (msqid == -1) {
             if (errno != EINVAL && errno != EACCES)
                 errMsg("msgctl-MSG_STAT");              /* Unexpected error */
             continue;                                   /* Ignore this item */
         }
 
         printf("%4d %8d  0x%08lx %7ld\n", ind, msqid,
                 (unsigned long) ds.msg_perm.__key, (long) ds.msg_qnum);
     }
 
     exit(EXIT_SUCCESS);
 }

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