netdev - Re: [PATCH net] geneve: Refine MTU limit

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Message-ID: <CAEh+42i628VNoXh5=vtFKzqVGeF4NqY3=GKbdNVeqmYnWK_oBg@mail.gmail.com>
Date:	Tue, 16 Feb 2016 10:32:15 -0800
From:	Jesse Gross <jesse@...nel.org>
To:	David Wragg <david@...ve.works>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	ovs dev <dev@...nvswitch.org>,
	Tom Herbert <tom@...bertland.com>
Subject: Re: [PATCH net] geneve: Refine MTU limit

On Tue, Feb 16, 2016 at 4:33 AM, David Wragg <david@...ve.works> wrote:
> diff --git a/drivers/net/geneve.c b/drivers/net/geneve.c
> index 028e387..f57f9bc 100644
> --- a/drivers/net/geneve.c
> +++ b/drivers/net/geneve.c
> @@ -37,6 +37,9 @@ MODULE_PARM_DESC(log_ecn_error, "Log packets received with corrupted ECN");
>
>  #define GENEVE_VER 0
>  #define GENEVE_BASE_HLEN (sizeof(struct udphdr) + sizeof(struct genevehdr))
> +#define GENEVE_MAX_OPTIONS_LEN (63 * 4)
> +#define GENEVE_MAX_MTU (IP_MAX_MTU - sizeof(struct iphdr) - GENEVE_BASE_HLEN \
> +                                               - GENEVE_MAX_OPTIONS_LEN)

In addition to Tom's comment about taking into account
dev->hard_header_len, can you please not include
GENEVE_MAX_OPTIONS_LEN in the MTU calculation based on the discussion
on the other thread? Otherwise, you are excluding some potentially
valid configurations.