doc: clarification about setting SO_ZEROCOPY

Signed-off-by: Kornilios Kourtis <kou@zurich.ibm.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/networking/msg_zerocopy.rst b/Documentation/networking/msg_zerocopy.rst
index 77f6d7e..291a012 100644 (file)
--- 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
 ------------