netdev - Re: [PATCH net-next v8 03/24] ovpn: add basic netlink support

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Message-ID: <fd952c28-1f17-45da-bd64-48917a7db651@openvpn.net>
Date: Tue, 8 Oct 2024 10:01:40 +0200
From: Antonio Quartulli <antonio@...nvpn.net>
To: Jiri Pirko <jiri@...nulli.us>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Donald Hunter <donald.hunter@...il.com>,
 Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
 sd@...asysnail.net, ryazanov.s.a@...il.com
Subject: Re: [PATCH net-next v8 03/24] ovpn: add basic netlink support

Hi,

On 07/10/24 17:32, Jiri Pirko wrote:
> Wed, Oct 02, 2024 at 11:02:17AM CEST, antonio@...nvpn.net wrote:
> 
> [...]
> 
> 
>> +operations:
>> +  list:
>> +    -
>> +      name: dev-new
>> +      attribute-set: ovpn
>> +      flags: [ admin-perm ]
>> +      doc: Create a new interface of type ovpn
>> +      do:
>> +        request:
>> +          attributes:
>> +            - ifname
>> +            - mode
>> +        reply:
>> +          attributes:
>> +            - ifname
>> +            - ifindex
>> +    -
>> +      name: dev-del
> 
> Why you expose new and del here in ovn specific generic netlink iface?
> Why can't you use the exising RTNL api which is used for creation and
> destruction of other types of devices?

That was my original approach in v1, but it was argued that an ovpn 
interface needs a userspace program to be configured and used in a 
meaningful way, therefore it was decided to concentrate all iface mgmt 
APIs along with the others in the netlink family and to not expose any 
RTNL ops.

However, recently we decided to add a dellink implementation for better 
integration with network namespaces and to allow the user to wipe a 
dangling interface.

In the future we are planning to also add the possibility to create a 
"persistent interface", that is an interface created before launching 
any userspace program and that survives when the latter is stopped.
I can guess this functionality may be better suited for RTNL, but I am 
not sure yet.

@Jiri: do you have any particular opinion why we should use RTNL ops and 
not netlink for creating/destroying interfaces? I feel this is mostly a 
matter of taste, but maybe there are technical reasons we should consider.

Thanks a lot for your contribution.

Regards,

> 
> 
> ip link add [link DEV | parentdev NAME] [ name ] NAME
> 		    [ txqueuelen PACKETS ]
> 		    [ address LLADDR ]
> 		    [ broadcast LLADDR ]
> 		    [ mtu MTU ] [index IDX ]
> 		    [ numtxqueues QUEUE_COUNT ]
> 		    [ numrxqueues QUEUE_COUNT ]
> 		    [ netns { PID | NETNSNAME | NETNSFILE } ]
> 		    type TYPE [ ARGS ]
> 
> ip link delete { DEVICE | dev DEVICE | group DEVGROUP } type TYPE [ ARGS ]
> 
> Lots of examples of existing types creation is for example here:
> https://developers.redhat.com/blog/2018/10/22/introduction-to-linux-interfaces-for-virtual-networking
> 
> 
> 
>> +      attribute-set: ovpn
>> +      flags: [ admin-perm ]
>> +      doc: Delete existing interface of type ovpn
>> +      do:
>> +        pre: ovpn-nl-pre-doit
>> +        post: ovpn-nl-post-doit
>> +        request:
>> +          attributes:
>> +            - ifindex
> 
> [...]

-- 
Antonio Quartulli
OpenVPN Inc.