Re: [PATCH mptcp-next v3 5/8] mptcp: userspace pm set_flags id support

[Matthieu Baerts <matttbe@kernel.org>]

On 08/01/2025 19:47, Matthieu Baerts wrote:
> Hi Geliang,
> 
> On 08/01/2025 05:21, Geliang Tang wrote:
>> From: Geliang Tang <tanggeliang@kylinos.cn>
>>
>> Similar to in-kernel PM, this patch adds address ID support to set_flags()
>> interface of userspace PM, allowing it to work with either an address or
>> an address ID.
>>
>> When an address ID is used, mptcp_userspace_pm_lookup_addr_by_id() helper
>> is used to look up the address entry in the local address list instead of
>> using mptcp_userspace_pm_lookup_addr().
> 
> Mmh, I'm still not sure about that. As I was saying in [1], if I'm not
> mistaken, with the userspace PM, it is possible not to find any entries
> here, e.g.: if a subflow using this address has not been added or the
> address has not been announced. (I guess the initial address is not
> there then).
> 
> Do you think this patch is worth it? Setting by ID for the in-kernel PM
> makes sense: unique ID for the netns, easier to type the ID than the
> full address. While for the userspace PM, it will be managed by a daemon
> that will have to track addresses anyway.
> 
> Or in other words, do you have a use-case for this? To me, it looks like
> "yes, you can only set the ID, but it might not always work". Then maybe
> better to always set the full address, no?
> 
> [1]
> https://lore.kernel.org/mptcp/d01d0e8a-5606-4152-aabe-32e4402adeeb@kernel.org/

Note: if we drop this patch (I think it is better), maybe patch 8/8 is
not worth it: not to have a "common" section with plenty of 'if
(token)', no? Or do you really need them for the BPF PM?

Cheers,
Matt
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