From 8866991164690817cc1e3489b6f7aa615170935d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nikola=20Forr=C3=B3?= <nforro@redhat.com>
Date: Wed, 10 Jan 2018 11:38:35 +0100
Subject: [PATCH] recvmmsg.2, sendmmsg.2: point out that error handling is
 unreliable

---
 man-pages/man2/recvmmsg.2 | 10 ++++++++++
 man-pages/man2/sendmmsg.2 |  9 +++++++++
 2 files changed, 19 insertions(+)

diff --git a/man-pages/man2/recvmmsg.2 b/man-pages/man2/recvmmsg.2
index 4c00ebe..7fc4d5a 100644
--- a/man-pages/man2/recvmmsg.2
+++ b/man-pages/man2/recvmmsg.2
@@ -162,6 +162,8 @@ In addition, the following error can occur:
 .B EINVAL
 .I timeout
 is invalid.
+.PP
+See also BUGS.
 .SH VERSIONS
 The
 .BR recvmmsg ()
@@ -170,6 +172,14 @@ Support in glibc was added in version 2.12.
 .SH CONFORMING TO
 .BR recvmmsg ()
 is Linux-specific.
+.SH BUGS
+If an error occurs after at least one message has been received,
+the call succeeds, and returns the number of messages received.
+The error code is expected to be returned on a subsequent call to
+.BR recvmmsq ().
+In the current implementation, however, the error code can be overwritten
+in the meantime by an unrelated network event on a socket,
+for example an incoming ICMP packet.
 .SH EXAMPLE
 .PP
 The following program uses
diff --git a/man-pages/man2/sendmmsg.2 b/man-pages/man2/sendmmsg.2
index a646524..939ee3c 100644
--- a/man-pages/man2/sendmmsg.2
+++ b/man-pages/man2/sendmmsg.2
@@ -134,6 +134,7 @@ is set to indicate the error.
 Errors are as for
 .BR sendmsg (2).
 An error is returned only if no datagrams could be sent.
+See also BUGS.
 .\" commit 728ffb86f10873aaf4abd26dde691ee40ae731fe
 .\"     ... only return an error if no datagrams could be sent.
 .\"     If less than the requested number of messages were sent, the application
@@ -165,6 +166,14 @@ is capped to
 .\"     For error handling an application using sendmmsg needs to retry at
 .\"     the first unsent message, so capping is simpler and requires less
 .\"     application logic than returning EINVAL.
+.SH BUGS
+If an error occurs after at least one message has been sent,
+the call succeeds, and returns the number of messages sent.
+The error code is lost.
+The caller can retry the transmission,
+starting at the first failed message, but there is no guarantee that,
+if an error is returned, it will be the same as the one that was lost
+on the previous call.
 .SH EXAMPLE
 The example below uses
 .BR sendmmsg ()
-- 
2.13.6