netdev - Re: Weird DHCP related problems with net-next

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Date:	Wed, 10 Jun 2015 15:04:03 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Scott Feldman <sfeldma@...il.com>
CC:	Andrew Lunn <andrew@...n.ch>, Netdev <netdev@...r.kernel.org>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: Weird DHCP related problems with net-next

On 10/06/15 14:44, Scott Feldman wrote:
> On Tue, Jun 9, 2015 at 5:12 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
> 
> 
>> I see the problem now, DSA does not implement a port_obj_add callback,
>> so when net/ipv4/fib_trie.c::switchdev_fib_ipv4_add() gets to call
>> switchdev_port_obj_add, we return -EOPNOTSUPP, and take the error path
>> in fib_table_insert thus not inserting the route for this interface.
> 
> Yup, that's the problem.
> 
>> Now when I restart the DHCP client, we end-up inserting the default
>> route which is correct, still figuring out what is different here,
>> probably the deletion of the routes by the DHCP client script first is
>> the different condition.
> 
> After the first failure, ipv4.fib_offload_disabled is set, so the next
> time switchdev_fib_ipv4_add() just returns 0 and the route is
> installed.  That explains the one-off behavior.
> 
>> At any rate, since switchdev_fib_ipv4_add() returns something that make
>> us take an error path in the fib_trie, something like this seems to fix
>> it for me but I am not well versed enough into the IPv4 routing code to
>> be 100% confident this is the right fix. Also, there are other callers
>> of switchdev_port_obj_add() but a quick look seems to make them safe as
>> they are only called for "offloading" capable hardware.
> 
> Your fix looks good to me.  The other users of
> switchdev_port_obj_add() want to return -EOPNOTSUPP to user, so it's
> just this one case for IPv4 fib insert/del where we'll want to treat
> no support silently.  Are you going to resend as patch for net-next,
> or should I?

I would prefer if you submitted it since you explained how things are
working and now everything makes sense. I will be happy to test it and
provide the magic tags ;)
-- 
Florian
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