msgids(2) [opensolaris man page]

msgids(2)							   System Calls 							 msgids(2)

NAME

       msgids - discover all message queue identifiers

SYNOPSIS

       #include <sys/msg.h>

       int msgids(int *buf, uint_t nids, uint_t  *pnids);

DESCRIPTION

       The  msgids()  function copies all active message queue identifiers from the system into the user-defined buffer specified by buf, provided
       that the number of such identifiers is not greater than the number of integers the buffer can contain, as specified by nids.  If  the  size
       of the buffer is insufficient to contain all of the active message queue identifiers in the system, none are copied.

       Whether or not the size of the buffer is sufficient to contain all of them, the number of active message queue identifiers in the system is
       copied into the unsigned integer pointed to by pnids.

       If nids is 0 or less than the number of active message queue identifiers in the system, buf is ignored.

RETURN VALUES

       Upon successful completion, msgids() returns 0.	Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The msgids() function will fail if:

       EFAULT	 The buf or pnids argument points to an illegal address.

USAGE

       The msgids() function returns a snapshot of all the active message queue identifiers in the system.  More may be  added	and  some  may	be
       removed before they can be used by the caller.

EXAMPLES

       Example 1 msgids() example

       This is sample C code indicating how to use the msgids() function (see msgsnap(2)):

	 void
	 examine_queues()
	 {
	      int *ids = NULL;
	      uint_t nids = 0;
	      uint_t n;
	      int i;

	      for (;;) {
		   if (msgids(ids, nids, &n) != 0) {
			perror("msgids");
			exit(1);
		   }
		   if (n <= nids)     /* we got them all */
			break;
		   /* we need a bigger buffer */
		   ids = realloc(ids, (nids = n) * sizeof (int));
	      }

	      for (i = 0; i < n; i++)
		   process_msgid(ids[i]);

	      free(ids);
	 }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ipcrm(1), ipcs(1), Intro(2), msgctl(2), msgget(2), msgsnap(2), msgrcv(2), msgsnd(2), attributes(5)

SunOS 5.11							    8 Mar 2000								 msgids(2)

msgsnap(2)							   System Calls 							msgsnap(2)

NAME

       msgsnap - message queue snapshot operation

SYNOPSIS

       #include <sys/msg.h>

       msgsnap(int msqid, void *buf, size_t bufsz, long msgtyp);

DESCRIPTION

       The  msgsnap()  function  reads all of the messages of type msgtyp from the queue associated with the message queue identifier specified by
       msqid and places them in the user-defined buffer pointed to by buf.

       The buf argument points to a user-defined buffer that on return will contain first a buffer header structure:

       struct msgsnap_head {
	    size_t  msgsnap_size;   /* bytes used/required in the buffer */
	    size_t  msgsnap_nmsg;   /* number of messages in the buffer */
       };

       followed by msgsnap_nmsg messages, each of which starts with a message header:

       struct msgsnap_mhead {
	    size_t  msgsnap_mlen;   /* number of bytes in the message */
	    long    msgsnap_mtype;  /* message type */
       };

       and followed by msgsnap_mlen bytes containing the message contents.

       Each subsequent message header is located at the first byte following the previous message contents, rounded up to a sizeof(size_t)  bound-
       ary.

       The bufsz argument specifies the size  of buf in bytes.	If bufsz is less than sizeof(msgsnap_head), msgsnap() fails with EINVAL.  If bufsz
       is insufficient to contain all of the requested messages, msgsnap() succeeds but returns with msgsnap_nmsg set to 0 and	with  msgsnap_size
       set to the required size of the buffer in bytes.

       The msgtyp argument specifies the types of messages requested as follows:

	 o  If msgtyp is 0, all of the messages on the queue are read.

	 o  If msgtyp is greater than 0, all messages of type msgtyp are read.

	 o  If msgtyp is less than 0, all messages with type less than or equal to the absolute value of msgtyp are read.

       The msgsnap() function is a non-destructive operation.  Upon completion, no changes are made to the data structures associated with msqid.

RETURN VALUES

       Upon successful completion, msgsnap() returns 0.  Otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

       The msgsnap() function will fail if:

       EACCES	       Operation permission is denied to the calling process.  See intro(2).

       EINVAL	       The msqid argument is not a valid message queue identifier or the value of bufsz is less than sizeof(struct msgsnap_head).

       EFAULT	       The buf argument points to an illegal address.

USAGE

       The  msgsnap()  function returns a snapshot of messages on a message queue at one point in time.  The queue contents can change immediately
       following return from msgsnap().

EXAMPLES

       Example 1: msgsnap() example

       This is sample C code indicating how to use the msgsnap function (see msgids(2)).

       void
       process_msgid(int msqid)
       {
	    size_t bufsize;
	    struct msgsnap_head *buf;
	    struct msgsnap_mhead *mhead;
	    int i;

	    /* allocate a minimum-size buffer */
	    buf = malloc(bufsize = sizeof(struct msgsnap_head));

	    /* read all of the messages from the queue */
	    for (;;) {
		 if (msgsnap(msqid, buf, bufsize, 0) != 0) {
		      perror("msgsnap");
			   free(buf);
			   return;
		 }
		 if (bufsize >= buf->msgsnap_size)  /* we got them all */
		      break;
		 /* we need a bigger buffer */
		 buf = realloc(buf, bufsize = buf->msgsnap_size);
	    }

	    /* process each message in the queue (there may be none) */
	    mhead = (struct msgsnap_mhead *)(buf + 1);	/* first message */
	    for (i = 0; i < buf->msgsnap_nmsg; i++) {
		 size_t mlen = mhead->msgsnap_mlen;

		 /* process the message contents */
		 process_message(mhead->msgsnap_mtype, (char *)(mhead+1), mlen);

		 /* advance to the next message header */
		 mhead = (struct msgsnap_mhead *)
		      ((char *)mhead + sizeof(struct msgsnap_mhead) +
		      ((mlen + sizeof(size_t) - 1) & ~(sizeof(size_t) - 1)));
	    }

	    free(buf);
       }

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ipcrm(1), ipcs(1), intro(2), msgctl(2), msgget(2), msgids(2), msgrcv(2), msgsnd(2), attributes(5)

SunOS 5.10							    8 Mar 2000								msgsnap(2)