172 lines
4.7 KiB
Groff
172 lines
4.7 KiB
Groff
.\" $NetBSD: msgsnd.2,v 1.15 2004/05/13 10:20:58 wiz Exp $
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.\"
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.\" Copyright (c) 1995 Frank van der Linden
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project
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.\" by Frank van der Linden
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd August 17, 1995
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.Dt MSGSND 2
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.Os
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.Sh NAME
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.Nm msgsnd
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.Nd send a message to a message queue
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/msg.h
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.Ft int
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.Fn msgsnd "int msqid" "const void *msgp" "size_t msgsz" "int msgflg"
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.Sh DESCRIPTION
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The
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.Fn msgsnd
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function sends a message from the message queue specified in
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.Fa msqid .
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.Fa msgp
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points to a user-defined structure containing the message.
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This structure must contain a first field of type
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.Sy long
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that will indicate the user-defined type of the message.
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The remaining fields will contain the contents of the message.
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The following is an example of what this user-defined
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structure might look like:
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.Bd -literal
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struct mymsg {
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long mtype; /* message type */
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char mtext[1]; /* body of message */
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};
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.Ed
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.Pp
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.Va mtype
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is an integer greater than 0 that can be used for selecting messages (see
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.Xr msgrcv 2 ) .
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.Va mtext
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is an array of bytes, with size up to the system limit
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.Dv MSGMAX .
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.Pp
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If the number of bytes already on the message queue plus
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.Fa msgsz
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is greater than the maximum number of bytes in the message queue
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.Pf ( Va msg_qbytes ,
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see
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.Xr msgctl 2 ) ,
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or if the number of messages on all queues system-wide is already equal to
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the system limit,
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.Fa msgflg
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determines the action of
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.Fn msgsnd .
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If
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.Fa msgflg
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has
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.Dv IPC_NOWAIT
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mask set in it, the call will return immediately.
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If
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.Fa msgflg
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does not have
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.Dv IPC_NOWAIT
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set in it, the call will block until:
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.Bl -bullet
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.It
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The condition which caused the call to block no longer exists.
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The message was sent.
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.It
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The message queue is removed, in which case \-1 will be returned and
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.Va errno
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set to
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.Er EINVAL .
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.It
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The caller catches a signal.
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The call returns with
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.Va errno
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set to
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.Er EINTR .
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.El
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.Pp
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After a successful call, the data structure associated with the message
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queue is updated in the following way:
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.Bl -bullet
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.It
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.Va msg_qnum
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is incremented by 1.
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.It
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.Va msg_lspid
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is set to the pid of the calling process.
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.It
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.Va msg_stime
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is set to the current time.
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.El
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.Sh RETURN VALUES
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Upon successful completion, 0 is returned.
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Otherwise, \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn msgsnd
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Fa msqid
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is not a valid message queue identifier,
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or the value of
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.Fa mtype
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is less than 1.
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.Pp
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The message queue was removed while
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.Fn msgsnd
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was waiting for a resource to become available in order to deliver the
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message.
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.Pp
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.Fa msgsz
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is less than 0, or greater than
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.Va msg_qbytes .
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.It Bq Er EACCES
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The calling process does not have write access to the message queue.
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.It Bq Er EAGAIN
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There was no space for this message either on the queue or in the whole
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system, and
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.Dv IPC_NOWAIT
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was set in
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.Fa msgflg .
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.It Bq Er EFAULT
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.Fa msgp
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points to an invalid address.
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.It Bq Er EINTR
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The system call was interrupted by the delivery of a signal.
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.El
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.Sh SEE ALSO
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.Xr msgctl 2 ,
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.Xr msgget 2 ,
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.Xr msgrcv 2
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.Sh STANDARDS
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The
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.Nm
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system call conforms to
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.St -xsh5 .
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.Sh HISTORY
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Message queues appeared in the first release of
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.At V .
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