mq_notify.3: Document the POSIX.1-2008 optional EINVAL error

POSIX.1-2008 allows an optional EINVAL error if
notification==NULL and the caller is not currently
registered to receive notifications.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man3/mq_notify.3 b/man3/mq_notify.3
index 1b5df1a9d3923d79189606ffa96db5047cd5ea8e..d5f20a484db9b0b90295267f1ec26aef6a0a5f80 100644 (file)
--- a/man3/mq_notify.3
+++ b/man3/mq_notify.3
@@ -192,6 +192,17 @@ is not a valid signal number.
 .TP
 .B ENOMEM
 Insufficient memory.
+.PP
+POSIX.1-2008 says that an implementation
+.I may
+generate an
+.B EINVAL
+.\" Linux does not do this
+error if
+.I notification
+is NULL, and the caller is not currently registered to receive
+notifications for the queue
+.IR mqdes .
 .SH CONFORMING TO
 POSIX.1-2001.
 .SH EXAMPLE