[LEDE-DEV] [OpenWrt-Devel] [PATCH netifd 2/3] interface: Only teardown interfaces having no proto task when l3_dev link lost

[Yousong Zhou]

On 14/07/2016, Felix Fietkau <nbd at nbd.name> wrote:
> On 2016-07-14 13:28, Hans Dedecker wrote:
>> On Thu, Jul 14, 2016 at 12:01 PM, Yousong Zhou <yszhou4tech at gmail.com>
>> wrote:
>>> On 14 July 2016 at 16:14, Hans Dedecker <dedeckeh at gmail.com> wrote:
>>>> Commit c6858766 adds teardown support when l3_dev link is lost
>>>> especially for shell protocols
>>>> that have no proto task. However shell protocols which have a proto task
>>>> running like ppp will
>>>> also be teared down which is not always the expected action.
>>>> As an example the PPP daemon can be put into persist state trying to
>>>> re-establish the link via
>>>> a hold off mechanism which is not possible when the daemon is terminated
>>>> by the proto shell
>>>> teardown.
>>>> Therefore restrict the teardown action for shell protocols having no
>>>> proto task.
>>>>
>>>
>>> How about adding an extra flag like managed-link, persistent-link,
>>> on-demand-link?  It looks to me doing teardown at link-down is more
>>> common a case.
>> Initially I was thinking about adding another flag like you propose
>> but then I was doubting if the change in behavior for shell protocols
>> having a proto task task was on purpose or not. In case of PPP and
>> link failure you don't want an immediate restart by netifd in some
>> cases (see https://github.com/lede-project/source/pull/200) as PPP
>> daemon can take care of the link re-negotiation based on a holdoff
>> timeout.
>> Additionally if the wan link loses connectivity a link down
>> notification will be received on the main device which will teardown
>> the protocol. Anyway I'm open for suggestions which way to go forward.
> Yousong,
>
> please provide some more details on where your commit c6858766 is
> actually needed/useful. In all the use cases I can think of, handling
> setup/teardown based on the l2 dev should be enough.
>
> - Felix
>

The issue them was that when l2tp-xxx went down, netifd has no proto
task state to be notified of, and main_dev state seemed unchanged.  If
I remeber and understand the code correcly other pppd shell protos do
teardown because of proto task event, not any device link state, and I
thought it's reasonable and  should not hurt to do an explicit
teardown on link down.

-- 
                yousong