Index: lib/libc/sys/mq_open.2
===================================================================
--- lib/libc/sys/mq_open.2
+++ lib/libc/sys/mq_open.2
@@ -37,7 +37,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd September 28, 2019
+.Dd October 15, 2021
 .Dt MQ_OPEN 2
 .Os
 .Sh NAME
@@ -272,6 +272,13 @@
 or
 .Va mq_msgsize
 was less than or equal to zero.
+.It Bq Er EINVAL
+Successfully opening the named message queue would cause
+.Va kern.mqueue.maxmq ,
+.Va kern.mqueue.maxmsgsize ,
+or
+.Va kern.mqueue.maxmsg
+to be exceeded.
 .It Bq Er EMFILE
 Too many message queue descriptors or file descriptors are currently in use
 by this process.
@@ -291,6 +298,20 @@
 .It Bq Er ENOSPC
 There is insufficient space for the creation of the new message queue.
 .El
+.Sh SYSCTL VARIABLES
+.Bl -tag -width "kern.mqueue.maxmsgsize"
+.It Va kern.mqueue.maxmq
+The maximum number of message queues.
+The default is 100.
+.It Va kern.mqueue.maxmsgsize
+The maximum size of a message, in bytes.
+The default is 16384.
+.It Va kern.mqueue.maxmsg
+The maximum number of messages in a queue.
+The default is 100.
+.It Va kern.mqueue.curmq
+The current number of message queues.
+.El
 .Sh SEE ALSO
 .Xr mq_close 2 ,
 .Xr mq_getattr 2 ,
@@ -300,7 +321,8 @@
 .Xr mq_unlink 2 ,
 .Xr mq_timedreceive 3 ,
 .Xr mq_timedsend 3 ,
-.Xr mqueuefs 5
+.Xr mqueuefs 5 ,
+.Xr sysctl 8
 .Sh STANDARDS
 The
 .Fn mq_open