Re: [PATCH] net: Add default_advmss() methods to blackhole dst_ops

[Changli Gao]

On Fri, Feb 18, 2011 at 5:57 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>
>
> I suspect following patch is needed
>
> CC Roland Dreier <roland@xxxxxxxxxxxxxxx> because he fixed the
> default_mtu problem in commit ec831ea72ee5d7d47
> (net: Add default_mtu() methods to blackhole dst_ops)
>
> Thanks !
>
> [PATCH] net: Add default_advmss() methods to blackhole dst_ops
>
> Commit 0dbaee3b37e118a (net: Abstract default ADVMSS behind an
> accessor.) introduced a possible crash in tcp_connect_init(), when
> dst->default_advmss() is called from dst_metric_advmss()
>
> Reported-by: George Spelvin <linux@xxxxxxxxxxx>
> Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> CC: Roland Dreier <roland@xxxxxxxxxxxxxxx>
> ---
>  net/ipv4/route.c |    7 +++++++
>  net/ipv6/route.c |    6 ++++++
>  2 files changed, 13 insertions(+)
>
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index 788a3e7..5edb605 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2712,6 +2712,12 @@ static unsigned int ipv4_blackhole_default_mtu(const struct dst_entry *dst)
>        return 0;
>  }
>
> +static unsigned int ipv4_blackhole_default_advmss(const struct dst_entry *dst)
> +{
> +       return 256;
> +}
> +
> +

I am wondering why magic number 256 is used here. Is there a special
reason? Thanks.

-- 
Regards,
Changli Gao(xiaosuo@xxxxxxxxx)
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