From c08e49611a8b4e38a75bf217e1029a48faf10b82 Mon Sep 17 00:00:00 2001 From: Andrew Morton <akpm@osdl.org> Date: Fri, 31 Mar 2006 02:09:36 -0800 Subject: [PATCH] [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> --- net/core/sock.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/net/core/sock.c b/net/core/sock.c index a96ea7dd0fc1b..ed2afdb9ea2df 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 -- 2.30.2