netdev - Re: [PATCH net] sit: use ipv6_mod_enabled to check if ipv6 is disabled

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Date:   Sun, 24 Feb 2019 20:24:51 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Hangbin Liu <liuhangbin@...il.com>, netdev@...r.kernel.org
Cc:     Stefano Brivio <sbrivio@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsa@...ulusnetworks.com>
Subject: Re: [PATCH net] sit: use ipv6_mod_enabled to check if ipv6 is
 disabled



On 02/24/2019 08:12 PM, Hangbin Liu wrote:
> ipv6_mod_enabled() is more safe and gentle to check if ipv6 is disabled
> at running time.
> 


Why is it better exactly ?

IPv6 can be enabled on the host, but disabled per device

/proc/sys/net/ipv6/conf/{name}/disable_ipv6


> Fixes: 173656accaf5 ("sit: check if IPv6 enabled before calling ip6_err_gen_icmpv6_unreach()")
> Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
> ---
>  net/ipv6/sit.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
> index e8a1dabef803..eea1f19985a7 100644
> --- a/net/ipv6/sit.c
> +++ b/net/ipv6/sit.c
> @@ -546,7 +546,7 @@ static int ipip6_err(struct sk_buff *skb, u32 info)
>  	}
>  
>  	err = 0;
> -	if (__in6_dev_get(skb->dev) &&
> +	if (ipv6_mod_enabled() &&
>  	    !ip6_err_gen_icmpv6_unreach(skb, iph->ihl * 4, type, data_len))
>  		goto out;
>  
>