netdev - [PATCH] doc: clarification about setting SO

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Message-Id: <20180109085222.GA6585@yvoz.zurich.ibm.com>
Date:   Tue, 9 Jan 2018 09:52:22 +0100
From:   Kornilios Kourtis <kou@...ich.ibm.com>
To:     netdev@...r.kernel.org
Cc:     Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH] doc: clarification about setting SO_ZEROCOPY

Signed-off-by: Kornilios Kourtis <kou@...ich.ibm.com>
---
 Documentation/networking/msg_zerocopy.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/networking/msg_zerocopy.rst b/Documentation/networking/msg_zerocopy.rst
index 77f6d7e..c3380f4 100644
--- a/Documentation/networking/msg_zerocopy.rst
+++ b/Documentation/networking/msg_zerocopy.rst
@@ -72,6 +72,10 @@ this flag, a process must first signal intent by setting a socket option:
 	if (setsockopt(fd, SOL_SOCKET, SO_ZEROCOPY, &one, sizeof(one)))
 		error(1, errno, "setsockopt zerocopy");
 
+Setting the socket option only works when the socket is in its initial
+(TCP_CLOSED) state.  Trying to set the option for a socket returned by accept(),
+for example, will lead to an EBUSY error. In this case, the option should be set
+to the listening socket and it will be inherited by the accepted sockets.
 
 Transmission
 ------------
-- 
2.4.3