Added man pages for msgctl(3), msgget(3), msgrcv(3) and msgsnd(3).

Obtained from: NetBSD

5 files changed, 656 insertions, 1 deletions

diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index 542028c..95e773b 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -46,7 +46,9 @@ MAN3+=	gen/alarm.3 gen/clock.3 gen/confstr.3 gen/config_open.3 \
 	gen/getmntinfo.3 gen/getnetgrent.3 gen/getpagesize.3 gen/getpass.3 \
 	gen/getpwent.3 gen/getttyent.3 gen/getvfsent.3 gen/getusershell.3 \
 	gen/glob.3 \
-	gen/initgroups.3 gen/isinf.3 gen/ldexp.3 gen/modf.3 gen/nice.3 \
+	gen/initgroups.3 gen/isinf.3 gen/ldexp.3 \
+	gen/msgctl.3 gen/msgget.3 gen/msgrcv.3 gen/msgsnd.3 \
+	gen/modf.3 gen/nice.3 \
 	gen/nlist.3 gen/pause.3 gen/popen.3 gen/psignal.3 gen/pwcache.3 \
 	gen/raise.3 gen/rand48.3 gen/scandir.3 gen/setjmp.3 gen/setmode.3 \
 	gen/siginterrupt.3 gen/signal.3 gen/sigsetops.3 gen/sleep.3 \
diff --git a/lib/libc/gen/msgctl.3 b/lib/libc/gen/msgctl.3
new file mode 100644
index 0000000..27da57c
--- /dev/null
+++ b/lib/libc/gen/msgctl.3
@@ -0,0 +1,201 @@
+.\"	$NetBSD: msgctl.2,v 1.1 1995/10/16 23:49:15 jtc Exp $	
+.\"
+.\" Copyright (c) 1995 Frank van der Linden
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"      This product includes software developed for the NetBSD Project
+.\"      by Frank van der Linden
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"/
+.Dd August 17, 1995
+.Dt MSGCTL 3
+.Os NetBSD
+.Sh NAME
+.Nm msgctl
+.Nd message control operations
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/ipc.h>
+.Fd #include <sys/msg.h>
+.Ft int
+.Fn msgctl "int msqid" "int cmd" "struct msqid_ds *buf"
+.Sh DESCRIPTION
+The
+.Fn msgctl
+system call performs some control operations on the message queue specified
+by
+.Fa msqid .
+
+Each message queue has a data structure associated with it, parts of which
+may be altered by
+.Fn msgctl
+and parts of which determine the actions of
+.Fn msgctl .
+The data structure is defined in
+.Aq Pa sys/msg.h
+and contains (amongst others) the following members:
+.Bd -literal
+struct msqid_ds {
+    struct ipc_perm msg_perm;	/* msg queue permission bits */
+    u_long msg_cbytes; /* # of bytes in use on the queue */
+    u_long msg_qnum;   /* # of msgs in the queue */
+    u_long msg_qbytes; /* max # of bytes on the queue */
+    pid_t  msg_lspid;  /* pid of last msgsnd() */
+    pid_t  msg_lrpid;  /* pid of last msgrcv() */
+    time_t msg_stime;  /* time of last msgsnd() */
+    time_t msg_rtime;  /* time of last msgrcv() */
+    time_t msg_ctime;  /* time of last msgctl() */
+};
+.Ed
+
+The
+.Bf -literal
+ipc_perm
+.Ef
+structure used inside the
+.Bf -literal
+shmid_ds
+.Ef
+structure is defined in
+.Aq Pa sys/ipc.h
+and looks like this:
+.Bd -literal
+struct ipc_perm {
+    ushort cuid; /* creator user id */
+    ushort cgid; /* creator group id */
+    ushort uid;	 /* user id */
+    ushort gid;	 /* group id */
+    ushort mode; /* permission (9 bits, see chmod(2)) */
+    ushort seq;	 /* sequence # (to generate unique id) */
+    key_t key;	 /* user specified msg/sem/shm key */
+};
+.Ed
+
+The operation to be performed by
+.Fn msgctl
+is specified in
+.Fa cmd
+and is one of:
+.Bl -tag -width IPC_RMIDX
+.It Dv IPC_STAT
+Gather information about the message queue and place it in the
+structure pointed to by
+.Fa buf .
+.It Dv IPC_SET
+Set the value of the
+.Va msg_perm.uid ,
+.Va msg_perm.gid ,
+.Va msg_perm.mode
+and
+.Va msg_qbytes
+fields in the structure associated with
+.Fa msqid .
+The values are taken from the corresponding fields in the structure
+pointed to by
+.Fa buf .
+This operation can only be executed by the super-user, or a process that
+has an effective user id equal to either 
+.Va msg_perm.cuid
+or
+.Va msg_perm.uid
+in the data structure associated with the message queue.
+The value of
+.Va msg_qbytes
+can only be increased by the super-user. Values for
+.Va msg_qbytes
+that exceed the system limit (MSGMNB from
+.Aq Pa sys/msg.h )
+are silently truncated to that limit.
+
+.It Dv IPC_RMID
+Remove the message queue specified by
+.Fa msqid
+and destroy the data associated with it. Only the super-user or a process
+with an effective uid equal to the 
+.Va msg_perm.cuid
+or
+.Va msg_perm.uid
+values in the data structure associated with the queue can do this.
+.El
+
+The permission to read from or write to a message queue (see
+.Xr msgsnd 3
+and
+.Xr msgrcv 3 )
+is determined by the
+.Va msg_perm.mode
+field in the same way as is
+done with files (see
+.Xr chmod 2 ),
+but the effective uid can match either the
+.Va msg_perm.cuid
+field or the
+.Va msg_perm.uid
+field, and the
+effective gid can match either
+.Va msg_perm.cgid
+or
+.Va msg_perm.gid .
+.Sh RETURN VALUES
+Upon successful completion, a value of 0 is returned. Otherwise, -1 is
+returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Fn msgctl
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EPERM
+.Fa cmd
+is equal to IPC_SET or IPC_RMID and the caller is not the super-user, nor does
+the effective uid match either the
+.Va msg_perm.uid
+or
+.Va msg_perm.cuid
+fields of the data structure associated with the message queue.
+
+An attempt is made to increase the value of
+.Va msg_qbytes
+through IPC_SET
+but the caller is not the super-user.
+.It Bq Er EACCESS
+The command is IPC_STAT
+and the caller has no read permission for this message queue.
+.It Bq Er EINVAL
+.Fa msqid
+is not a valid message queue identifier.
+
+.Va cmd
+is not a valid command.
+.It Bq Er EFAULT
+.Fa buf
+specifies an invalid address.
+.El
+.Sh SEE ALSO
+.Xr msgsnd 3 ,
+.Xr msgrcv 3 ,
+.Xr msgget 3
+.Sh HISTORY
+Message queues appeared in the first release of AT&T Unix System V.
diff --git a/lib/libc/gen/msgget.3 b/lib/libc/gen/msgget.3
new file mode 100644
index 0000000..41a7202
--- /dev/null
+++ b/lib/libc/gen/msgget.3
@@ -0,0 +1,126 @@
+.\"	$NetBSD: msgget.2,v 1.1 1995/10/16 23:49:19 jtc Exp $	
+.\"
+.\" Copyright (c) 1995 Frank van der Linden
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"      This product includes software developed for the NetBSD Project
+.\"      by Frank van der Linden
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"/
+.Dd August 17, 1995
+.Dt MSGGET 3
+.Os NetBSD
+.Sh NAME
+.Nm msgget
+.Nd get message queue
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/ipc.h>
+.Fd #include <sys/msg.h>
+.Ft int
+.Fn msgget "key_t key" "int msgflg"
+.Sh DESCRIPTION
+.Fn msgget
+returns the message queue identifier associated with
+.Fa key .
+A message queue identifier is a unique integer greater than zero.
+
+A message queue is created if either
+.Fa key
+is equal to IPC_PRIVATE, or
+.Fa key
+does not have a message queue identifier associated with it, and the IPC_CREAT
+bit is set in
+.Fa msgflg.
+
+If a new message queue is created, the data structure associated with it (the
+.Va msqid_ds
+structure, see
+.Xr msgctl 3 )
+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 .
+.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
+(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 EACESS
+A message queue is already associated with
+.Fa key
+and the caller has no permission to access it.
+.It Bq Er EEXIST
+Both IPC_CREAT and 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
+IPC_CREAT was not set in
+.Fa msgflg
+and no message queue associated with
+.Fa key
+was found.
+.El
+.Sh SEE ALSO
+.Xr msgctl 3 ,
+.Xr msgrcv 3 ,
+.Xr msgsnd 3
+.Sh HISTORY
+Message queues appeared in the first release of AT&T Unix System V.
diff --git a/lib/libc/gen/msgrcv.3 b/lib/libc/gen/msgrcv.3
new file mode 100644
index 0000000..db61fab
--- /dev/null
+++ b/lib/libc/gen/msgrcv.3
@@ -0,0 +1,181 @@
+.\"	$NetBSD: msgrcv.2,v 1.1 1995/10/16 23:49:20 jtc Exp $	
+.\"
+.\" Copyright (c) 1995 Frank van der Linden
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"      This product includes software developed for the NetBSD Project
+.\"      by Frank van der Linden
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"/
+.Dd August 17, 1995
+.Dt MSGRCV 3
+.Os NetBSD
+.Sh NAME
+.Nm msgrcv
+.Nd receive a message from a message queue
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/ipc.h>
+.Fd #include <sys/msg.h>
+.Ft int
+.Fn msgrcv "int msqid" "void *msgp" "size_t msgsz" "long msgtyp" "int msgflg"
+.Sh DESCRIPTION
+The 
+.Fn msgrcv
+function receives a message from the message queue specified in
+.Fa msqid ,
+and places it into the structure pointed to by
+.Fa msgp .
+This structure should consist of the following members:
+.Bd -literal
+    long mtype;    /* message type */
+    char mtext[1]; /* body of message */
+.Ed
+
+.Va mtype
+is an integer greater than 0 that can be used for selecting messages,
+.Va mtext
+is an array of bytes, with a size up to that of the system limit (MSGMAX).
+
+The value of
+.Fa msgtyp
+has one of the following meanings:
+.Bl -bullet
+.It
+.Fa msgtyp
+is greater than 0. The first message of type
+.Fa msgtyp
+will be received.
+.It
+.Fa msgtyp
+is equal to 0. The first message on the queue will be received.
+.It
+.Fa msgtyp
+is less than 0. The first message of the lowest message type that is
+less than or equal to the absolute value of
+.Fa msgtyp
+will be received.
+.El
+
+.Fa msgsz
+specifies the maximum length of the requested message. If the received
+message has a length greater than
+.Fa msgsz
+it will be silently truncated if the MSG_NOERROR flag is set in
+.Fa msgflg ,
+otherwise an error will be returned.
+
+If no matching message is present on the message queue specified by
+.Fa msqid ,
+the behavior of
+.Fn msgrcv
+depends on whether the IPC_NOWAIT flag is set in
+.Fa msgflg
+or not. If IPC_NOWAIT is set,
+.Fn msgrcv
+will immediately return a value of -1, and set
+.Va errno
+to EAGAIN. If IPC_NOWAIT is not set, the calling process will be blocked
+until:
+.Bl -bullet
+.It
+A message of the requested type becomes available on the message queue.
+.It
+The message queue is removed, in which case -1 will be returned, and
+.Va errno
+set to EINVAL.
+.It
+A signal is received and caught. -1 is returned, and
+.Va errno
+set to EINTR.
+.El
+
+If a message is successfully received, the data structure associated with
+.Fa msqid
+is updated as follows:
+.Bl -bullet
+.It
+.Va msg_cbytes
+is decremented by the size of the message.
+.It
+.Va msg_lrpid
+is set to the pid of the caller.
+.It
+.Va msg_lrtime
+is set to the current time.
+.It
+.Va msg_qnum
+is decremented by 1.
+.Sh RETURN VALUES
+Upon successful completion,
+.Fn msgrcv
+returns the number of bytes received into the
+.Va mtext
+field of the structure pointed to by
+.Fa msgp .
+Otherwise, -1 is returned, and
+.Va errno
+set to indicate the error.
+.Sh ERRORS
+.Fn msgrcv
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa msqid
+is not a valid message queue identifier
+
+The message queue was removed while
+.Fn msgrcv
+was waiting for a message of the requested type to become available on it.
+
+.Fa msgsz
+is less than 0.
+.It Bq Er E2BIG
+A matching message was received, but its size was greater than
+.Fa msgsz
+and the MSG_NOERROR flag was not set in
+.Fa msgflg .
+.It Bq Er EACCESS
+The calling process does not have read access to the message queue.
+.It Bq Er EFAULT
+.Fa msgp
+points to an invalid address.
+.It Bq Er EINTR
+The system call was interrupted by the delivery of a signal.
+.It Bq Er EAGAIN
+There is no message of the requested type available on the message queue,
+and IPC_NOWAIT is set in
+.Fa msgflg .
+.Sh SEE ALSO
+.Xr msgsnd 3 ,
+.Xr msgctl 3 ,
+.Xr msgget 3
+.Sh BUGS
+NetBSD and FreeBSD do not define the EIDRM error value, which should be used in
+the case of a removed message queue, nor the ENOMSG value, which
+should be used when no suitable message is available and IPC_NOWAIT
+is set.
+.Sh HISTORY
+Message queues appeared in the first release of AT&T Unix System V.
diff --git a/lib/libc/gen/msgsnd.3 b/lib/libc/gen/msgsnd.3
new file mode 100644
index 0000000..b97a313
--- /dev/null
+++ b/lib/libc/gen/msgsnd.3
@@ -0,0 +1,145 @@
+.\"	$NetBSD: msgsnd.2,v 1.1 1995/10/16 23:49:24 jtc Exp $	
+.\"
+.\" Copyright (c) 1995 Frank van der Linden
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"      This product includes software developed for the NetBSD Project
+.\"      by Frank van der Linden
+.\" 4. The name of the author may not be used to endorse or promote products
+.\"    derived from this software without specific prior written permission
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+.\"/
+.Dd August 17, 1995
+.Dt MSGSND 3
+.Os NetBSD
+.Sh NAME
+.Nm msgsnd
+.Nd send a message to a message queue
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <sys/ipc.h>
+.Fd #include <sys/msg.h>
+.Ft int
+.Fn msgsnd "int msqid" "void *msgp" "size_t msgsz" "int msgflg"
+.Sh DESCRIPTION
+The 
+.Fn msgsnd
+function sends a message from the message queue specified in
+.Fa msqid .
+.Fa msgp
+points to a structure containing the message. This structure should
+consist of the following members:
+.Bd -literal
+    long mtype;    /* message type */
+    char mtext[1]; /* body of message */
+.Ed
+
+.Va mtype
+is an integer greater than 0 that can be used for selecting messages (see
+.Xr msgrcv 3 ) ,
+.Va mtext 
+is an array of bytes, with a size up to that of the system limit (MSGMAX).
+
+If the number of bytes already on the message queue plus
+.Fa msgsz
+is bigger than the maximum number of bytes on the message queue (
+.Va msg_qbytes ,
+see
+.Xr msgctl 3 ) ,
+or the number of messages on all queues system-wide is already equal to
+the system limit,
+.Fa msgflg
+determines the action of
+.Fn msgsnd .
+If
+.Fa msgflg
+has IPC_NOWAIT mask set in it, the call will return immediately. If
+.Fa msgflg
+does not have IPC_NOWAIT set in it, the call will block until:
+.Bl -bullet
+.It
+The condition which caused the call to block does no longer exist.
+The message will be sent.
+.It
+The message queue is removed, in which case -1 will be returned, and
+.Va errno
+is set to EINVAL.
+.It
+The caller catches a signal. The call returns with
+.Va errno
+set to EINTR.
+.El
+
+After a successful call, the data structure associated with the message
+queue is updated in the following way:
+.Bl -bullet
+.It
+.Va msg_cbytes
+is incremented by the size of the message.
+.It
+.Va msg_qnum
+is incremented by 1.
+.It
+.Va msg_lspid
+is set to the pid of the calling process.
+.It
+.Va msg_stime
+is set to the current time.
+.El
+.Sh RETURN VALUES
+Upon successful completion, 0 is returned. Otherwise, -1 is returned and
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Fn msgsnd
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+.Fa msqid
+is not a valid message queue identifier
+
+The message queue was removed while
+.Fn msgsnd
+was waiting for a resource to become available in order to deliver the
+message.
+
+.Fa msgsz
+is less than 0, or greater than
+.Va msg_qbytes .
+.It Bq Er EACCESS
+The calling process does not have write access to the message queue.
+.It Bq Er EAGAIN
+There was no space for this message either on the queue, or in the whole
+system, and IPC_NOWAIT was set in
+.Fa msgflg .
+.It Bq Er EFAULT
+.Fa msgp
+points to an invalid address.
+.It Bq Er EINTR
+The system call was interrupted by the delivery of a signal.
+.El
+.Sh BUGS
+NetBSD and FreeBSD do not define the EIDRM error value, which should be used
+in the case of a removed message queue.
+.Sh HISTORY
+Message queues appeared in the first release of AT&T Unix System V.