svmsg/svmsg_ls.c

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

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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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