netdev - Re: [PATCH net-next] ipv6: addrconf: use stable address generator for ARPHRD

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Date:	Thu, 17 Dec 2015 23:04:56 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Bjørn Mork <bjorn@...k.no>, netdev@...r.kernel.org
Cc:	吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
Subject: Re: [PATCH net-next] ipv6: addrconf: use stable address generator for
 ARPHRD_NONE

On 16.12.2015 16:44, Bjørn Mork wrote:
> Add a new address generator mode, using the stable address generator
> with an automatically generated secret. This is intended as a default
> address generator mode for device types with no EUI64 implementation.
> The new generator is used for ARPHRD_NONE interfaces initially, adding
> default IPv6 autoconf support to e.g. tun interfaces.
> 
> If the addrgenmode is set to 'random', either by default or manually,
> and no stable secret is available, then a random secret is used as
> input for the stable-privacy address generator.  The secret can be
> read and modified like manually configured secrets, using the proc
> interface.  Modifying the secret will change the addrgen mode to
> 'stable-privacy' to indicate that it operates on a known secret.
> 
> Existing behaviour of the 'stable-privacy' mode is kept unchanged. If
> a known secret is available when the device is created, then the mode
> will default to 'stable-privacy' as before.  The mode can be manually
> set to 'random' but it will behave exactly like 'stable-privacy' in
> this case. The secret will not change.
> 
> Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Cc: 吉藤英明 <hideaki.yoshifuji@...aclelinux.com>
> Signed-off-by: Bjørn Mork <bjorn@...k.no>
> ---
> Changes since RFC:
>  - use IN6_ADDR_GEN_MODE_RANDOM as requested
>  - set the device type specific default in addrconf_dev_config() instead
>    of ipv6_add_dev() to catch device type changes
> 
> I guess an explanation is needed for the last change: My primary
> use case for this is the raw-ip support recently added to the qmi_wwan
> driver. This driver creates an ARPHRD_ETHER device which can be morphed
> into an ARPHRD_NONE device. So at device creation time everything is
> fine and EUI64 is supported. But when the link is set up, the device
> type is change and EUI64 does not work. So I needed to override the
> default for ARPHRD_NONE at link up time.
> 
> An alternative would be to keep the ipv6_add_dev() code and add device
> type change notifier code. That seemed messier to me. Besides, we
> already do type based address configuration decisions in
> addrconf_dev_config(), deciding whether autoconfiguration is available
> or not.

Agreed to your statements above and I reviewed the patch. Also, I can't
see any bad side effects resulting in ARPHRD_NONE interfaces picking up
link local addresses in general.

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Thanks,
Hannes

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