| MSGSND(2) | System Calls Manual | MSGSND(2) | 
msgsnd —
#include <sys/msg.h>
int
  
  msgsnd(int
    msqid, const void
    *msgp, size_t
    msgsz, int
  msgflg);
msgsnd() function sends a message from the message
  queue specified in msqid. The msgp
  argument is a pointer to a user-defined structure containing the message. This
  structure must contain a first field of type long that
  will indicate the user-defined type of the message. The remaining fields will
  contain the contents of the message. The following is an example of what this
  user-defined structure might look like:
struct mymsg {
    long mtype;    /* message type */
    char mtext[1]; /* body of message */
};
The mtype field is an integer greater than 0
    that can be used for selecting messages (see
    msgrcv(2)). The
    mtext field is an array of bytes of length
    msgsz, with size up to the system limit
    MSGMAX.
If the number of bytes already on the message queue plus
    msgsz is greater than the maximum number of bytes in
    the message queue (msg_qbytes, see
    msgctl(2)), or if the number
    of messages on all queues system-wide is already equal to the system limit,
    msgflg determines the action of
    msgsnd(). If msgflg has
    IPC_NOWAIT mask set in it, the call will return
    immediately. If msgflg does not have
    IPC_NOWAIT set in it, the call will block until:
EINVAL.EINTR.After a successful call, the data structure associated with the message queue is updated in the following way:
msgsnd() will fail if:
EACCES]EAGAIN]IPC_NOWAIT was set in
      msgflg.EFAULT]EINTR]EINVAL]The message queue was removed while
        msgsnd() was waiting for a resource to become
        available in order to deliver the message.
The msgsz argument is greater than
        msg_qbytes or
      SSIZE_MAX.
msgsnd system call conforms to
  X/Open System Interfaces and Headers Issue 5
  (“XSH5”) and IEEE Std 1003.1-2001
  (“POSIX.1”).
| July 24, 2013 | NetBSD 9.4 |