Date:   Mon, 25 May 2020 11:48:07 +0000
From:   Horatiu Vultur <horatiu.vultur@...rochip.com>
To:     Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
CC:     <roopa@...ulusnetworks.com>, <davem@...emloft.net>,
        <kuba@...nel.org>, <andrew@...n.ch>,
        <UNGLinuxDriver@...rochip.com>,
        <bridge@...ts.linux-foundation.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: MRP netlink interface

The 05/25/2020 12:33, Nikolay Aleksandrov wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 25/05/2020 14:28, Horatiu Vultur wrote:
> > Hi,
> >
> > While I was working on adding support for MRA role to MRP, I noticed that I
> > might have some issues with the netlink interface, so it would be great if you
> > can give me an advice on how to continue.
> >
> > First a node with MRA role can behave as a MRM(Manager) or as a
> > MRC(Client). The behaviour is decided by the priority of each node. So
> > to have this functionality I have to extend the MRP netlink interface
> > and this brings me to my issues.
> >
> > My first approach was to extend the 'struct br_mrp_instance' with a field that
> > contains the priority of the node. But this breaks the backwards compatibility,
> > and then every time when I need to change something, I will break the backwards
> > compatibility. Is this a way to go forward?
> >
> > Another approach is to restructure MRP netlink interface. What I was thinking to
> > keep the current attributes (IFLA_BRIDGE_MRP_INSTANCE,
> > IFLA_BRIDGE_MRP_PORT_STATE,...) but they will be nested attributes and each of
> > this attribute to contain the fields of the structures they represents.
> > For example:
> > [IFLA_AF_SPEC] = {
> >     [IFLA_BRIDGE_FLAGS]
> >     [IFLA_BRIDGE_MRP]
> >         [IFLA_BRIDGE_MRP_INSTANCE]
> >             [IFLA_BRIDGE_MRP_INSTANCE_RING_ID]
> >             [IFLA_BRIDGE_MRP_INSTANCE_P_IFINDEX]
> >             [IFLA_BRIDGE_MRP_INSTANCE_S_IFINDEX]
> >         [IFLA_BRIDGE_MRP_RING_ROLE]
> >             [IFLA_BRIDGE_MRP_RING_ROLE_RING_ID]
> >             [IFLA_BRIDGE_MRP_RING_ROLE_ROLE]
> >         ...
> > }
> > And then I can parse each field separately and then fill up the structure
> > (br_mrp_instance, br_mrp_port_role, ...) which will be used forward.
> > Then when this needs to be extended with the priority it would have the
> > following format:
> > [IFLA_AF_SPEC] = {
> >     [IFLA_BRIDGE_FLAGS]
> >     [IFLA_BRIDGE_MRP]
> >         [IFLA_BRIDGE_MRP_INSTANCE]
> >             [IFLA_BRIDGE_MRP_INSTANCE_RING_ID]
> >             [IFLA_BRIDGE_MRP_INSTANCE_P_IFINDEX]
> >             [IFLA_BRIDGE_MRP_INSTANCE_S_IFINDEX]
> >             [IFLA_BRIDGE_MRP_INSTANCE_PRIO]
> >         [IFLA_BRIDGE_MRP_RING_ROLE]
> >             [IFLA_BRIDGE_MRP_RING_ROLE_RING_ID]
> >             [IFLA_BRIDGE_MRP_RING_ROLE_ROLE]
> >         ...
> > }
> > And also the br_mrp_instance will have a field called prio.
> > So now, if the userspace is not updated to have support for setting the prio
> > then the kernel will use a default value. Then if the userspace contains a field
> > that the kernel doesn't know about, then it would just ignore it.
> > So in this way every time when the netlink interface will be extended it would
> > be backwards compatible.
> >
> > If it is not possible to break the compatibility then the safest way is to
> > just add more attributes under IFLA_BRIDGE_MRP but this would just complicate
> > the kernel and the userspace and it would make it much harder to be extended in
> > the future.
> >
> > My personal choice would be the second approach, even if it breaks the backwards
> > compatibility. Because it is the easier to go forward and there are only 3
> > people who cloned the userspace application
> > (https://github.com/microchip-ung/mrp/graphs/traffic). And two of
> > these unique cloners is me and Allan.
> >
> > So if you have any advice on how to go forward it would be great.
> >
> 
> IIRC this is still in net-next only, right? If so - now would be the time to change it.
> Once it goes into a release, we'll be stuck with workarounds. So I'd go for solution 2).

Yes, this is only in net-next. Then I should ASAP update this with
solution 2.

> 
> I haven't cloned it, but I do sync your user-space mrp repo to check against the patches. :)
> 

-- 
/Horatiu

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