xref: /freebsd/lib/libsys/msgget.2 (revision 8269e7673cf033aba67dab8264fe719920c70f87)

.\"	$NetBSD: msgget.2,v 1.1 1995/10/16 23:49:19 jtc Exp $
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.\" Copyright (c) 1995 Frank van der Linden
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.\"      by Frank van der Linden
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.Dd March 4, 2018
.Dt MSGGET 2
.Os
.Sh NAME
.Nm msgget
.Nd get message queue
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/msg.h
.Ft int
.Fn msgget "key_t key" "int msgflg"
.Sh DESCRIPTION
The
.Fn msgget
function
returns the message queue identifier associated with
.Fa key .
A message queue identifier is a unique integer greater than zero.
.Pp
A message queue is created if either
.Fa key
is equal to
.Dv IPC_PRIVATE ,
or
.Fa key
does not have a message queue identifier associated with it, and the
.Dv IPC_CREAT
bit is set in
.Fa msgflg .
.Pp
If a new message queue is created, the data structure associated with it (the
.Va msqid_ds
structure, see
.Xr msgctl 2 )
is initialized as follows:
.Bl -bullet
.It
.Va msg_perm.cuid
and
.Va msg_perm.uid
are set to the effective uid of the calling process.
.It
.Va msg_perm.gid
and
.Va msg_perm.cgid
are set to the effective gid of the calling process.
.It
.Va msg_perm.mode
is set to the lower 9 bits of
.Fa msgflg
which are set by ORing these constants:
.Bl -tag -width 0000
.It Dv 0400
Read access for user.
.It Dv 0200
Write access for user.
.It Dv 0040
Read access for group.
.It Dv 0020
Write access for group.
.It Dv 0004
Read access for other.
.It Dv 0002
Write access for other.
.El
.It
.Va msg_cbytes ,
.Va msg_qnum ,
.Va msg_lspid ,
.Va msg_lrpid ,
.Va msg_rtime ,
and
.Va msg_stime
are set to 0.
.It
.Va msg_qbytes
is set to the system wide maximum value for the number of bytes in a queue
.Pf ( Dv MSGMNB ) .
.It
.Va msg_ctime
is set to the current time.
.El
.Sh RETURN VALUES
Upon successful completion a positive message queue identifier is returned.
Otherwise, -1 is returned and the global variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EACCES
A message queue is already associated with
.Fa key
and the caller has no permission to access it.
.It Bq Er EEXIST
Both
.Dv IPC_CREAT
and
.Dv IPC_EXCL
are set in
.Fa msgflg ,
and a message queue is already associated with
.Fa key .
.It Bq Er ENOSPC
A new message queue could not be created because the system limit for
the number of message queues has been reached.
.It Bq Er ENOENT
.Dv IPC_CREAT
was not set in
.Fa msgflg
and no message queue associated with
.Fa key
was found.
.El
.Sh SEE ALSO
.Xr msgctl 2 ,
.Xr msgrcv 2 ,
.Xr msgsnd 2
.Sh HISTORY
Message queues appeared in the first release of
.At V .