Re: [PATCH] tcp: harmonize tcp_vx_rcv header length assumptions

Eric Dumazet
2010-01-12T10:46:13Z

Le 12/01/2010 11:05, William Allen Simpson a écrit :
> Harmonize tcp_v4_rcv() and tcp_v6_rcv() -- better document tcp doff and
> header length assumptions.
>
> Reduces multiply/shifts, marginally improving speed.
>
> Retains redundant tcp header length checks before checksumming.
>
> Stand-alone patch, originally developed for TCPCT.
>
> Requires:
> net: tcp_header_len_th and tcp_option_len_th
>
> Signed-off-by: William.Allen.Simpson@gmail.com
> ---
> net/ipv4/tcp_ipv4.c | 36 +++++++++++++++++++-------------
> net/ipv6/tcp_ipv6.c | 56
> ++++++++++++++++++++++++++++----------------------
> 2 files changed, 52 insertions(+), 40 deletions(-)

Seems fine, but :

1) What means the "Transformed ?" you wrote several times ?

2) This part :

- th = tcp_hdr(skb);
-
- if (th->doff < sizeof(struct tcphdr)/4)
+ /* Check bad doff, compare doff directly to constant value */
+ tcp_header_len = tcp_hdr(skb)->doff;
+ if (tcp_header_len < (sizeof(struct tcphdr) / 4))
goto bad_packet;
- if (!pskb_may_pull(skb, th->doff*4))
+
+ /* Check too short header and options */
+ tcp_header_len *= 4;
+ if (!pskb_may_pull(skb, tcp_header_len))
goto discard_it;

could be : (no need for 4 multiplies/divides)

tcp_header_len = tcp_header_len_th(tcp_hdr(skb));
if (tcp_header_len < sizeof(struct tcphdr))
goto bad_packet;
/* Check too short header and options */
if (!pskb_may_pull(skb, tcp_header_len))
goto discard_it;