1.\" $NetBSD: msgsnd.2,v 1.1 1995/10/16 23:49:24 jtc Exp $ 2.\" 3.\" Copyright (c) 1995 Frank van der Linden 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project 17.\" by Frank van der Linden 18.\" 4. The name of the author may not be used to endorse or promote products 19.\" derived from this software without specific prior written permission 20.\" 21.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 22.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 23.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 24.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 26.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 27.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 28.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 29.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 30.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 31.\" 32.\" $FreeBSD: src/lib/libc/gen/msgsnd.3,v 1.9.2.5 2001/12/14 18:33:51 ru Exp $ 33.\" 34.Dd January 4, 2015 35.Dt MSGSND 2 36.Os 37.Sh NAME 38.Nm msgsnd 39.Nd send a message to a message queue 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In sys/types.h 44.In sys/ipc.h 45.In sys/msg.h 46.Ft int 47.Fn msgsnd "int msqid" "const void *msgp" "size_t msgsz" "int msgflg" 48.Sh DESCRIPTION 49The 50.Fn msgsnd 51system call sends a message to the message queue specified in 52.Fa msqid . 53.Fa msgp 54points to a structure containing the message. 55This structure should 56consist of the following members: 57.Bd -literal 58 long mtype; /* message type */ 59 char mtext[1]; /* body of message */ 60.Ed 61.Pp 62.Va mtype 63is an integer greater than 0 that can be used for selecting messages (see 64.Xr msgrcv 2 ) , 65.Va mtext 66is an array of bytes, with a size up to that of the system limit 67.Pf ( Dv MSGMAX ) . 68.Pp 69If the number of bytes already on the message queue plus 70.Fa msgsz 71is bigger than the maximum number of bytes on the message queue 72.Pf ( Va msg_qbytes , 73see 74.Xr msgctl 2 ) , 75or the number of messages on all queues system-wide is already equal to 76the system limit, 77.Fa msgflg 78determines the action of 79.Fn msgsnd . 80If 81.Fa msgflg 82has 83.Dv IPC_NOWAIT 84mask set in it, the call will return immediately. 85If 86.Fa msgflg 87does not have 88.Dv IPC_NOWAIT 89set in it, the call will block until: 90.Bl -bullet 91.It 92The condition which caused the call to block does no longer exist. 93The message will be sent. 94.It 95The message queue is removed, in which case -1 will be returned, and 96.Va errno 97is set to 98.Er EINVAL . 99.It 100The caller catches a signal. 101The call returns with 102.Va errno 103set to 104.Er EINTR . 105.El 106.Pp 107After a successful call, the data structure associated with the message 108queue is updated in the following way: 109.Bl -bullet 110.It 111.Va msg_cbytes 112is incremented by the size of the message. 113.It 114.Va msg_qnum 115is incremented by 1. 116.It 117.Va msg_lspid 118is set to the pid of the calling process. 119.It 120.Va msg_stime 121is set to the current time. 122.El 123.Sh RETURN VALUES 124.Rv -std msgsnd 125.Sh ENVIRONMENT 126The XSI Interprocess Communication family of functions is also available 127as an implementation in userspace. 128To use it, the 129.Xr sysvipcd 8 130daemon has to be running. 131.Pp 132If the 133.Ev USR_SYSVIPC 134variable is set in a process' environment, the process and its children 135will use the userspace implementation. 136.Sh ERRORS 137.Fn msgsnd 138will fail if: 139.Bl -tag -width Er 140.It Bq Er EINVAL 141.Fa msqid 142is not a valid message queue identifier 143.Pp 144The message queue was removed while 145.Fn msgsnd 146was waiting for a resource to become available in order to deliver the 147message. 148.Pp 149.Fa msgsz 150is less than 0, or greater than 151.Va msg_qbytes . 152.Pp 153.Fa mtype 154is not greater than 0. 155.It Bq Er EACCES 156The calling process does not have write access to the message queue. 157.It Bq Er EAGAIN 158There was no space for this message either on the queue, or in the whole 159system, and 160.Dv IPC_NOWAIT 161was set in 162.Fa msgflg . 163.It Bq Er EFAULT 164.Fa msgp 165points to an invalid address. 166.It Bq Er EINTR 167The system call was interrupted by the delivery of a signal. 168.El 169.Sh HISTORY 170Message queues appeared in the first release of AT&T Unix System V. 171.Sh AUTHORS 172.An -nosplit 173The 174.Dx 175specific userspace implementation (see 176.Sx ENVIRONMENT ) 177was written by 178.An Larisa Grigore . 179.Sh BUGS 180.Nx , 181.Dx , 182and 183.Fx 184do not define the 185.Er EIDRM 186error value, which should be used 187in the case of a removed message queue. 188