netdev - Re: [PATCH RFC net-next 7/7] netdevsim: Add simple FIB resource controller via devlink

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Date:   Sat, 24 Mar 2018 17:02:38 +0100
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        roopa@...ulusnetworks.com, shm@...ulusnetworks.com,
        jiri@...lanox.com, idosch@...lanox.com,
        jakub.kicinski@...ronome.com, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH RFC net-next 7/7] netdevsim: Add simple FIB resource
 controller via devlink

Sat, Mar 24, 2018 at 04:05:38PM CET, dsa@...ulusnetworks.com wrote:
>On 3/24/18 1:26 AM, Jiri Pirko wrote:
>> Fri, Mar 23, 2018 at 04:13:14PM CET, dsa@...ulusnetworks.com wrote:
>>> On 3/23/18 9:05 AM, Jiri Pirko wrote:
>>>> Fri, Mar 23, 2018 at 04:03:40PM CET, dsa@...ulusnetworks.com wrote:
>>>>> On 3/23/18 9:01 AM, Jiri Pirko wrote:
>>>>>> Fri, Mar 23, 2018 at 03:31:02PM CET, dsa@...ulusnetworks.com wrote:
>>>>>>> On 3/23/18 12:50 AM, Jiri Pirko wrote:
>>>>>>>>> +void nsim_devlink_setup(struct netdevsim *ns)
>>>>>>>>> +{
>>>>>>>>> +	struct net *net = dev_net(ns->netdev);
>>>>>>>>> +	bool *reg_devlink = net_generic(net, nsim_devlink_id);
>>>>>>>>> +	struct devlink *devlink;
>>>>>>>>> +	int err = -ENOMEM;
>>>>>>>>> +
>>>>>>>>> +	/* only one device per namespace controls devlink */
>>>>>>>>> +	if (!*reg_devlink) {
>>>>>>>>> +		ns->devlink = NULL;
>>>>>>>>> +		return;
>>>>>>>>> +	}
>>>>>>>>> +
>>>>>>>>> +	devlink = devlink_alloc(&nsim_devlink_ops, 0);
>>>>>>>>> +	if (!devlink)
>>>>>>>>> +		return;
>>>>>>>>> +
>>>>>>>>> +	devlink_net_set(devlink, net);
>>>>>>>>> +	err = devlink_register(devlink, &ns->dev);
>>>>>>>>
>>>>>>>> This reg_devlink construct looks odd. Why don't you leave the devlink
>>>>>>>> instance in init_ns?
>>>>>>>
>>>>>>> It is a per-network namespace resource controller. Since struct devlink
>>>>>>
>>>>>> Wait a second. What do you mean by "per-network namespace"? Devlink
>>>>>> instance is always associated with one physical device. Like an ASIC.
>>>>>>
>>>>>>
>>>>>>> has a net entry, the simplest design is to put it into the namespace of
>>>>>>> the controller. Without it, controlling resource sizes in namespace
>>>>>>> 'foobar' has to be done from init_net, which is just wrong.
>>>>>
>>>>> you need to look at how netdevsim creates a device per netdevice.
>>>>
>>>> That means one devlink instance for each netdevsim device, doesn't it?
>>>>
>>>
>>> yes.
>> 
>> Still not sure how to handle namespaces in devlink. Originally, I
>> thought it would be okay to leave all devlink instances in init_ns.
>> Because what happens if you move netdev to another namespace? Should the
>> devlink move as well? What if you have multiple ports, each in different
>> namespace. Can user move devlink instance to another namespace? Etc.
>> 
>
>The devlink instance is associated with a 'struct device' and those do
>not change namespaces AFAIK.

Yeah. But you put devlink instance into namespace according to struct
net_device. That is mismatch.