From: Andrew Morton <akpm@osdl.org>
Date: Fri, 31 Mar 2006 10:09:36 +0000 (-0800)
Subject: [NET]: add SO_RCVBUF comment
X-Git-Tag: upstream/snapshot3+hdmi~41137^2~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=c08e49611a8b4e38a75bf217e1029a48faf10b82;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git

[NET]: add SO_RCVBUF comment

Put a comment in there explaining why we double the setsockopt()
caller's SO_RCVBUF.  People keep wondering.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/core/sock.c b/net/core/sock.c
index a96ea7d..ed2afdb 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -385,7 +385,21 @@ set_sndbuf:
 				val = sysctl_rmem_max;
 set_rcvbuf:
 			sk->sk_userlocks |= SOCK_RCVBUF_LOCK;
-			/* FIXME: is this lower bound the right one? */
+			/*
+			 * We double it on the way in to account for
+			 * "struct sk_buff" etc. overhead.   Applications
+			 * assume that the SO_RCVBUF setting they make will
+			 * allow that much actual data to be received on that
+			 * socket.
+			 *
+			 * Applications are unaware that "struct sk_buff" and
+			 * other overheads allocate from the receive buffer
+			 * during socket buffer allocation.
+			 *
+			 * And after considering the possible alternatives,
+			 * returning the value we actually used in getsockopt
+			 * is the most desirable behavior.
+			 */
 			if ((val * 2) < SOCK_MIN_RCVBUF)
 				sk->sk_rcvbuf = SOCK_MIN_RCVBUF;
 			else