netdev - Re: [PATCH] af_packet: account for VLAN when checking packet size

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Message-ID: <1286805782.2737.25.camel@edumazet-laptop>
Date:	Mon, 11 Oct 2010 16:03:02 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Phil Sutter <phil@....cc>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	johann.baudy@...-log.net
Subject: Re: [PATCH] af_packet: account for VLAN when checking packet size

Le lundi 11 octobre 2010 à 15:25 +0200, Phil Sutter a écrit :
> Signed-off-by: Phil Sutter <phil@....cc>
> ---
>  net/packet/af_packet.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 9a17f28..ad37754 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -56,6 +56,7 @@
>  #include <linux/in.h>
>  #include <linux/inet.h>
>  #include <linux/netdevice.h>
> +#include <linux/if_arp.h>
>  #include <linux/if_packet.h>
>  #include <linux/wireless.h>
>  #include <linux/kernel.h>
> @@ -983,6 +984,11 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>  
>  	reserve = dev->hard_header_len;
>  
> +	/* allow VLAN packets when device supports them */
> +	if (likely(dev->type == ARPHRD_ETHER) &&
> +	    likely(!(dev->features & NETIF_F_VLAN_CHALLENGED)))
> +		reserve += VLAN_HLEN;
> +
>  	err = -ENETDOWN;
>  	if (unlikely(!(dev->flags & IFF_UP)))
>  		goto out_put;

If we dont test ETH_P_8021Q protocol here, we allow sending 1504 bytes
frames for MTU=1500

Should we really care ?

If not, just do

reserve = dev->hard_header_len + VLAN_HLEN;



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