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

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Date:   Tue, 26 Feb 2019 12:08:00 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org,
        Stefano Brivio <sbrivio@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net] sit: use ipv6_mod_enabled to check if ipv6 is
 disabled

Hi David,
On Mon, Feb 25, 2019 at 07:15:26PM -0700, David Ahern wrote:
> On 2/25/19 6:55 PM, Hangbin Liu wrote:
> > Just as I said, this issue only occurs when IPv6 is disabled at boot time
> > as there is no IPv6 route entry. Disable ipv6 on specific interface should
> > not be affected(IPv6 route/fib has inited). So I think use ipv6_mod_enabled()
> > would be more suitable in this scenario. Did I miss something?
> 
> From a readability perspective the code path depends on whether ipv6 is
> enabled on the device. I think it is better to leave that as it is.

When I posted 173656accaf5 ("sit: check if IPv6 enabled before calling
ip6_err_gen_icmpv6_unreach()"), my purpose is to check if IPv6 disabled
at boot time. I didn't know we have ipv6_mod_enabled() at that time, so I
just used __in6_dev_get() as a trick way/work around.

A few days later I saw your commit e434863718d4 ("net: vrf: Fix crash when
IPv6 is disabled at boot time") and I thought this would be a more clear way
to tell people that we are checking if IPv6 disabled at boot time. So I posted
these two follow up fixes.

I don't know why you thought check IPv6 is enbled on the device is better.
Because it's more strict? Maybe I missed something here. But if you feel it
is better to leave as it it, then let's keep it.

Thanks
Hangbin