RFC for enablement of slpd on openbmc

Fri Oct 21 00:55:32 AEDT 2016

Hi Patrick,

Thanks for giving the feedback,please find my comments inline.

Regards
Ratan Gupta

On Thursday 20 October 2016 03:02 AM, Patrick Williams wrote:
> On Wed, Oct 19, 2016 at 11:19:26PM +0530, Ratan Gupta wrote:
>> *Enabling SLP Server on openBMC*
>>
>> What is SLP
>>
>> =======
>>
>> Service Location Protocol (SLP) is a protocol that provides a framework
>> to allow networking applications to discover the existence, location,
>> and configuration of networked services in enterprise networks.
>>
>> openSLP is widely accepted in the industry
> What are the aspects of SLP that are requirements for the intended
> use-case?  SLP as a protocol has both direct query and an optional
> "directory" implementation that aggregates SLP results.  In your
> experience is that necessary or used?
   Slp supports three agents
      1) UA(slptool)
      2) SA(in our case it would be new app which we have to write for 
reg of services)
      3) DA(where the reg info stores) it could be on network or on the 
same machine..but it is required to support the RFC.

>
> What is the anticipated size footprint of using openSLP?  The RFC
> doesn't seem that significant, so if we do not need the directory aspect
> might it be more beneficial to write a small daemon ourself to give SLP
> responses rather than trying to mold openSLP to fit our needs?
    runtime foot print TOP Command shows
    214     1 daemon   S *3620*   3%   0% slpd -l /tmp/slpd.log  >>>3.5K
    file size which will take in flash
    slpd:- 100.4K
    libslp:-69.7K
>
> I'm certainly not advocating avoiding using existing open source.  But,
> with there not being an update to openSLP since 2013 and all the aspects
> we are going to have to work around below, I'm wondering on the benefit.
   I think we are not doing any workaround here,It is slp (as per the 
RFC)which expects
   IP in their reg url as the slp needs ip in the reg url,we are 
catering that need via de
>> What do we need to do?
>>
>> ==============
>>
>> 1) Bring SLP(OpenSLP) in image:- Write the bitbake recipe(didn't find
>> the readily available bitbake recipe)
>>
>> 2) Configure the services through Settings daemon.
> We do have a .bbclass for "registration" we need to ensure that this is
> utilized for SLP as much as possible.
> Yes we would be using it
>
> 3) Write the .service file as it needs to start after network is
> up(after networkd-online.target)
> This service file is for the openslp daemon, correct?
Yes

How to configure the services which needs to be registered with slpd

============================================

Option 1:- settingsd

Note: Gives the flexibility to change the configured services @ runtime.
Do we require this functionality?

Option 2:conf file for discovery services

Note: During build time we can get the service info(service-name,port)
from the existing infra(discoveryservice.bbclass)

> I don't entirely understand how these aren't phases of the same
> solution.
>
> The problem space as I see it:
>      1. An application provides a service to be advertised by SLP.
>      2. The application is currently started via a .service or a .socket
>         file.
>              a. Some services are always running.
>              b. Some services use socket-activation.
>      3. We need to register this service with the SLP daemon, somehow.
>
> Do we need to ensure the application is running (or available to run via
> socket activation) before we do the registration?  If the application is
> being restarted should we remove the registration and add it back after
> it comes back?
I believe that is not needed as the application(SA) would be dependent 
on the conf
      and out policy suggest that network services should restart always 
so it would be unnecessary
      to do reg and unreg
>
> You mentioned dealing with IP address changes.  It is pretty annoying
> that openSLP doesn't do this for you (a custom daemon could).  How are
> you handling multiple network interfaces?  How to we flag internal vs
> external interfaces?  Isn't there a mechanism via systemd (or networkd) to
> identify when the ip address changes?  Ideally, this would be a restart
> of a .service.
>
> I could see us building a very small application that performs three
> functions:
>      1. slp-register register <service>
>      2. slp-register deregister <service>
>      3. slp-register ip-change
>
> For each registered service "foo.service", we can generate
> foo-slp-register.service.  The foo-slp-register.service will depend on
> foo.service, so it is started immediately after and stopped when the
> foo.service is stopped.  The 'start' will be to call 'slp-register
> register'  and the 'stop' will be to call 'slp-register deregister'.
>
> We also can then keep off of something in systemd / networkd to run
> 'slp-register ip-change' whenever the IP changes.  This could either
> restart *-slp-register.service or it could extract all of the SLP
> registrations and update them with new IP addresses.  Putting all of the
> *-slp-register.service into a 'target' might make restarting them very
> simple.
>
> With this approach we do not need a long running application.
I agree but do we really need to dereg and reg in the case when the 
service is going down as.
     Our service policy is restart always whenever the network service 
goes down. so service would be down for a moment
     Long running application i was asking for the IP change event,I am 
not aware if systemd-networkd send some event
     whenever the ip change occurs.
>> How to register the services
>> ==================
>>
>> 1) Static Registration:- will not work as we need ip/host-name details
>> which we don't have @build time.
> It is unfortunate about this.  We can solve this with a custom
> slp-daemon.
Agree but the custom one would not be implementing the full RFC.
>
>> 2) Application(new DBUS app) will register the configured services to
>> the slpd on startup.
> I am not understanding what the 'dbus app' aspect of this would be.
> What would be the dbus interfaces?
   I thought of if some other app(netman.py) wants to do the reg and 
unreg. so thought of exposing the
       Register Service
       unregister Service
       Raising the DBUS signal in case of IP change.
>> We need to provide the dynamic registration support on BMC as IP of BMC
>> can change any time.  Registration of services with slpd takes the URL
>> of the service which includes ip and port of the service which needs to
>> be registered.
>>
>> Create a DBUS service application
>>
>> =====================
>>
>> 1) Once the service starts it registers the configured services with slpd.
>>
>> 2) listening on RTNETLINK event for ip change: raise a dbus signal(for
>> the IP change)
> Who is getting this signal?
    This one was required,if certain application is interested in IP 
change event then it can use.
    today no application is interested in this event.
>
>>        if there is IP change then dereg the old service followed by reg
>> service as the ip has changed.
>>
>> Regards
>> Ratan Gupta

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