Re: dhcp integration into the platform


Jukka Rissanen
 

Hi Piotr,

On Tue, 2017-03-28 at 11:11 +0200, Piotr Mienkowski wrote:
Hi Marcus,

Thanks for your extensive and very well written emails. Looking at
this thread it's clear that there indeed "there are two different
world views of the conceptual purpose of net_if_up() and
net_if_down()."

To add to the discussion I would like to remind here one design issue
related to Ethernet drivers which, I belive, is not yet clarified. As
principle Ethernet drivers are initialized before the network stack
is. Currently the initialization process involves bringing up the
interface and establishing a functioning data link. If at that time
Ethernet driver receives an RX frame it will try to forward it to the
network stack even if it may not be initialized yet. That's a race
condition. One way to solve it would be to have an interface
enable/disable function. The data link would be established only when
it is explicitly requested by the network stack.
Currently the interface is marked UP when we are ready to receive
packets. So far this has worked well and I propose we keep it like
this.


As you have mentioned a few times already we also need to handle a
scenario where a user unplugs the network cable and plugs it in some
time later possibly on a different LAN. So also for me the option 2)
seems like a more natural way forward.

2) We keep the enable/disable semantic.  This implies:
- We split net_if_up/down into net_if_enable/disable() and
net_if_up/down() such that net_if_enable calls l2->enable() while
net_if_up/down deals with NET_IF_UP and raising
net_event_if_up/down
- The hardwired net_if_up() calls at network stack boot are
switched
to call net_if_enable()
- The BT L2 enable callback is used to turn advertising on/off
- Every network device needs to call net_if_up() once it has a link
established (and net_if_down when it drops). (BT already does this)
I'm only not sure how an interface power up / power down
functionality fits in here. In any case the final say belongs to the
network stack maintainers. 

Cheers,
Piotr
Cheers,
Jukka

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