Re: [RFC net-next Patch 0/3] net: bridge: mrp: Add support for Media Redundancy Protocol(MRP)

[Nikolay Aleksandrov]

On 10/01/2020 16:13, Nikolay Aleksandrov wrote:
> On 09/01/2020 17:06, Horatiu Vultur wrote:
>> Media Redundancy Protocol is a data network protocol standardized by
>> International Electrotechnical Commission as IEC 62439-2. It allows rings of
>> Ethernet switches to overcome any single failure with recovery time faster than
>> STP. It is primarily used in Industrial Ethernet applications.
>>
>> This is the first proposal of implementing a subset of the standard. It supports
>> only 2 roles of an MRP node. It supports only Media Redundancy Manager(MRM) and
>> Media Redundancy Client(MRC). In a MRP ring, each node needs to support MRP and
>> in a ring can be only one MRM and multiple MRC. It is possible to have multiple
>> instances of MRP on a single node. But a port can be part of only one MRP
>> instance.
>>
>> The MRM is responsible for detecting when there is a loop in the ring. It is
>> sending the frame MRP_Test to detect the loops. It would send MRP_Test on both
>> ports in the ring and if the frame is received at the other end, then the ring
>> is closed. Meaning that there is a loop. In this case it sets the port state to
>> BLOCKED, not allowing traffic to pass through except MRP frames. In case it
>> stops receiving MRP_Test frames from itself then the MRM will detect that the
>> ring is open, therefor it would notify the other nodes of this change and will
>> set the state of the port to be FORWARDING.
>>
>> The MRC is responsible for forwarding MRP_Test frames between the ring ports
>> (and not to flood on other ports) and to listen when there is a change in the
>> network to clear the FDB.
>>
>> Similar with STP, MRP is implemented on top of the bridge and they can't be
>> enable at the same time. While STP runs on all ports of the bridge, MRP needs to
>> run only on 2 ports.
>>
>> The bridge needs to:
>> - notify when the link of one of the ports goes down or up, because MRP instance
>>   needs to react to link changes by sending MRP_LinkChange frames.
>> - notify when one of the ports are removed from the bridge or when the bridge
>>   is destroyed, because if the port is part of the MRP ring then MRP state
>>   machine should be stopped.
>> - add a handler to allow MRP instance to process MRP frames, if MRP is enabled.
>>   This is similar with STP design.
>> - add logic for MRP frames inside the bridge. The bridge will just detect MRP
>>   frames and it would forward them to the upper layer to allow to process it.
>> - update the logic to update non-MRP frames. If MRP is enabled, then look also
>>   at the state of the port to decide to forward or not.
>>
>> To create a MRP instance on the bridge:
>> $ bridge mrp add dev br0 p_port eth0 s_port eth1 ring_role 2 ring_id 1
>>
>> Where:
>> p_port, s_port: can be any port under the bridge
>> ring_role: can have the value 1(MRC - Media Redundancy Client) or
>>            2(MRM - Media Redundancy Manager). In a ring can be only one MRM.
>> ring_id: unique id for each MRP instance.
>>
>> It is possible to create multiple instances. Each instance has to have it's own
>> ring_id and a port can't be part of multiple instances:
>> $ bridge mrp add dev br0 p_port eth2 s_port eth3 ring_role 1 ring_id 2
>>
>> To see current MRP instances and their status:
>> $ bridge mrp show
>> dev br0 p_port eth2 s_port eth3 ring_role 1 ring_id 2 ring_state 3
>> dev br0 p_port eth0 s_port eth1 ring_role 2 ring_id 1 ring_state 4
>>
>> If this patch series is well received, the in the future it could be extended
>> with the following:
>> - add support for Media Redundancy Automanager. This role allows a node to
>>   detect if needs to behave as a MRM or MRC. The advantage of this role is that
>>   the user doesn't need to configure the nodes each time they are added/removed
>>   from a ring and it adds redundancy to the manager.
>> - add support for Interconnect rings. This allow to connect multiple rings.
>> - add HW offloading. The standard defines 4 recovery times (500, 200, 30 and 10
>>   ms). To be able to achieve 30 and 10 it is required by the HW to generate the
>>   MRP_Test frames and detect when the ring is open/closed.
>>
>> Horatiu Vultur (3):
>>   net: bridge: mrp: Add support for Media Redundancy Protocol
>>   net: bridge: mrp: Integrate MRP into the bridge
>>   net: bridge: mrp: Add netlink support to configure MRP
>>
>>  include/uapi/linux/if_bridge.h |   27 +
>>  include/uapi/linux/if_ether.h  |    1 +
>>  include/uapi/linux/rtnetlink.h |    7 +
>>  net/bridge/Kconfig             |   12 +
>>  net/bridge/Makefile            |    2 +
>>  net/bridge/br.c                |   19 +
>>  net/bridge/br_device.c         |    3 +
>>  net/bridge/br_forward.c        |    1 +
>>  net/bridge/br_if.c             |   10 +
>>  net/bridge/br_input.c          |   22 +
>>  net/bridge/br_mrp.c            | 1517 ++++++++++++++++++++++++++++++++
>>  net/bridge/br_mrp_timer.c      |  227 +++++
>>  net/bridge/br_netlink.c        |    9 +
>>  net/bridge/br_private.h        |   30 +
>>  net/bridge/br_private_mrp.h    |  208 +++++
>>  security/selinux/nlmsgtab.c    |    5 +-
>>  16 files changed, 2099 insertions(+), 1 deletion(-)
>>  create mode 100644 net/bridge/br_mrp.c
>>  create mode 100644 net/bridge/br_mrp_timer.c
>>  create mode 100644 net/bridge/br_private_mrp.h
>>
> 
> Hi all,
> I agree with Stephen here, IMO you have to take note of how STP has progressed
> and that bringing it in the kernel was a mistake, these days mstpd has an active
> community and much better support which is being extended. This looks best implemented
> in user-space in my opinion with minimal kernel changes to support it. You could simply
> open a packet socket with a filter and work through that, you don't need new netlink
> sockets. I'm not familiar with the protocol so can't really be the judge of that, if
> you present a good argument for needing a new netlink socket for these packets - then
> sure, ok.

nevermind the last sentence (about packet/netlink), I misread your earlier reply :)

> 
> If you do decide to continue with the kernel version (which I would again discourage)
> a few general points (from a quick scan):
>  - the single 1.6+k line patch is just hard to review, please break it into more digestable
>    and logical pieces
>  - the locking is wrong, also there're a few use-after-free bugs 
>  - please re-work the bridge integration code, it can be simplified and tests can be eliminated
>  - your netlink helpers usage is generally wrong and needs more work
>  - use the already existing port states instead of adding new ones and you can avoid some tests in fast-path
>  - perhaps look into using br_afspec() for configuration/retrieval initially ? I don't think you need the new rtm messages yet.
>  - I'm sure I can go on, but I really think all of this should be put in user-space -
>    in-kernel STP is a great example of how _not_ to do it. :) As a bonus you'll avoid 90% of the
>    problems above just by making your own abstractions and using them for it.
> 
> 
> Thanks,
>  Nik
>