netdev - Re: [PATCH net] ipv6: set all.accept

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Date:   Tue, 14 Nov 2017 03:24:03 +0100
From:   Stefano Brivio <sbrivio@...hat.com>
To:     Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        Matteo Croce <mcroce@...hat.com>, Erik Kline <ek@...gle.com>
Subject: Re: [PATCH net] ipv6: set all.accept_dad to 0 by default

On Mon, 13 Nov 2017 14:45:36 +0100
Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:

> The commit a2d3f3e33853 modifies the way to disable dad on an interface.
> Before the patch, setting <iface>.accept_dad to 0 was enough to disable it.
> Because all.accept_dad is set to 1 by default, after the patch, the user
> needs to set both all.accept_dad and <iface>.accept_dad to 0 to disable it.

Perhaps it would make sense to be a bit more descriptive here, this
seems to have generated quite some confusion.

Besides, a2d3f3e33853 was just a fix-up for 35e015e1f577, which is
instead the change which actually changed the behaviour.

What about:

---
With commit 35e015e1f577 ("ipv6: fix net.ipv6.conf.all interface DAD
handlers"), the global 'accept_dad' flag is also taken into account
and set to 1 by default. If either global or per-interface flag is
non-zero, DAD will be enabled on a given interface.

This is not backward compatible: before 35e015e1f577, the user could
disable DAD just by setting the per-interface flag to 0. Now, the
user instead needs to set both flags to 0 to actually disable DAD.

Restore the previous behaviour by setting the default for the global
'accept_dad' flag to 0. This way, DAD is still enabled by default,
as per-interface flags are set to 1 on device creation, but setting
them to 0 is enough to disable DAD on a given interface.

- Before 35e015e1f577:
          global    per-interface    DAD enabled
[default]   1             1              yes
            X             0              no
            X             1              yes

- After 35e015e1f577:
          global    per-interface    DAD enabled
            0             0              no
            0             1              yes
            1             0              yes
[default]   1             1              yes

- After this fix:
          global    per-interface    DAD enabled
            0             0              no
[default]   0             1              yes
            1             0              yes
            1             1              yes
---

> Fixes: a2d3f3e33853 ("ipv6: fix net.ipv6.conf.all.accept_dad behaviour for real")

And I'd rather say:

Fixes: 35e015e1f577 ("ipv6: fix net.ipv6.conf.all interface DAD handlers")

> CC: Stefano Brivio <sbrivio@...hat.com>
> CC: Matteo Croce <mcroce@...hat.com>
> CC: Erik Kline <ek@...gle.com>
> Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>

With a more descriptive commit message and the appropriate Fixes:
reference, FWIW,

Acked-by: Stefano Brivio <sbrivio@...hat.com>

-- 
Stefano