Subject: [PATCH 002 of 3] knfsd: Avoid checksum checks when collecting metadata for a UDP packet.

From: NeilBrown <[email-masked]>
Date: Fri, 2 Mar 2007 15:28:30 +1100

When recv_msg is called with a size of 0 and MSG_PEEK (and
sunrpc/svcsock.c does), it is clear that we only interested in
metadata (from/to addresses) and not the data, so don't do any
checksum checking at this point.  Leave that until the data is
requested.

Signed-off-by: Neil Brown <[email-masked]>

### Diffstat output
 ./net/ipv4/udp.c |    3 +++
 ./net/ipv6/udp.c |    4 ++++
 2 files changed, 7 insertions(+)

diff .prev/net/ipv4/udp.c ./net/ipv4/udp.c
--- .prev/net/ipv4/udp.c	2007-03-02 14:20:13.000000000 +1100
+++ ./net/ipv4/udp.c	2007-03-02 15:13:50.000000000 +1100
@@ -846,6 +846,9 @@ try_again:
 			goto csum_copy_err;
 		copy_only = 1;
 	}
+	if (len == 0 &&  (flags & MSG_PEEK))
+		/* avoid checksum concerns when just getting metadata */
+		copy_only = 1;
 
 	if (copy_only)
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),

diff .prev/net/ipv6/udp.c ./net/ipv6/udp.c
--- .prev/net/ipv6/udp.c	2007-03-02 14:20:13.000000000 +1100
+++ ./net/ipv6/udp.c	2007-03-02 15:13:50.000000000 +1100
@@ -151,6 +151,10 @@ try_again:
 		copy_only = 1;
 	}
 
+	if (len == 0 &&  (flags & MSG_PEEK))
+		/* avoid checksum concerns when just getting metadata */
+		copy_only = 1;
+
 	if (copy_only)
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied       );

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