MSGSNAP man page on SmartOS

Man page or keyword search:  
man Server   16655 pages
apropos Keyword Search (all sections)
Output format
SmartOS logo
[printable version]

MSGSNAP(2)							    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) boundary.

       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  fol‐
       lows:

	   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)

				  Mar 8, 2000			    MSGSNAP(2)
[top]

List of man pages available for SmartOS

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net