ip: take care of last fragment in ip_append_data
While investigating a bit, I found ip_fragment() slow path was taken
because ip_append_data() provides following layout for a send(MTU +
N*(MTU - 20)) syscall :
- one skb with 1500 (mtu) bytes
- N fragments of 1480 (mtu-20) bytes (before adding IP header)
last fragment gets 17 bytes of trail data because of following bit:
if (datalen == length + fraggap)
alloclen += rt->dst.trailer_len;
Then esp4 adds 16 bytes of data (while trailer_len is 17... hmm...
another bug ?)
In ip_fragment(), we notice last fragment is too big (1496 + 20) > mtu,
so we take slow path, building another skb chain.
In order to avoid taking slow path, we should correct ip_append_data()
to make sure last fragment has real trail space, under mtu...
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index e427620..3551b6d 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -926,16 +926,19 @@
!(rt->dst.dev->features&NETIF_F_SG))
alloclen = mtu;
else
- alloclen = datalen + fragheaderlen;
+ alloclen = fraglen;
/* The last fragment gets additional space at tail.
* Note, with MSG_MORE we overallocate on fragments,
* because we have no idea what fragment will be
* the last.
*/
- if (datalen == length + fraggap)
+ if (datalen == length + fraggap) {
alloclen += rt->dst.trailer_len;
-
+ /* make sure mtu is not reached */
+ if (datalen > mtu - fragheaderlen - rt->dst.trailer_len)
+ datalen -= ALIGN(rt->dst.trailer_len, 8);
+ }
if (transhdrlen) {
skb = sock_alloc_send_skb(sk,
alloclen + hh_len + 15,