Re: [PATCH] dlm_controld: Support for extended value of kernel DLM_MAX_ADDR_COUNT

[Heming Zhao <heming.zhao@suse.com>]

On 2/25/25 22:19, Alexander Aring wrote:
> Hi,
> 
> On Tue, Feb 25, 2025 at 2:34 AM Heming Zhao <heming.zhao@suse.com> wrote:
>>
>> Hello Dave,
>>
>> On 2/25/25 14:27, Heming Zhao wrote:
>>> On 2/25/25 03:35, David Teigland wrote:
>>>> On Mon, Feb 24, 2025 at 10:27:04AM -0500, Alexander Aring wrote:
>>>>> What are we doing with the detect_protocol() change? You want to
>>>>> submit the current version again? I would like to test it with
>>>>> corosync 2 vs 3 with no configuration changes on an upgrade (if this
>>>>> is even possible).
>>>>
>>>> I suggest we stop trying to detect, and always use tcp unless protocol is
>>>> set to sctp.
>>>>
>>>> Dave
>>>>
>>>
>>> That's fine with me
>>> For corosync 3.x, there is a lot of work to support dynamic multi-link.
>>> However, to support config mode, the current dlm code only requires a few modifications.
>>>
>>> - Heming
>>
>> Following your idea, if TCP is used by default, what will happen when a user
>> sets up multiple links in Corosync 3.x without changing config file?
>> The TCP mode of the current DLM only accepts one link. Therefore, in this
>> scenario, DLM will refuse to run and report an error.
>>
>> Do you think we need to invest effort in changing the TCP mode code to allow
>> TCP to work when the Corosync layer sets up multiple links?
>> For example, to simplify the code, we could take only the first network link
>> from the Corosync callback and ignore the others. Or we could keep the current
>> behavior and prevent running in multi-link mode under TCP.
> 
> I would ignore the others, there exists ways to run multipath TCP on
> top of multiple TCP sockets (similar to what mptcp is doing but mptcp
> might be overkill, lookup "mptcp redudant scheduler").
> This can be future work, existing code regarding sequence numbers of
> dlm messages can be reused.
> 
> If somebody applies multiple links we assume any of them would work.
> Later additional handling as mentioned above could just begin to work
> in a magical way.
> 
> - Alex
> 

Let me summarize the above discussion/description:
- TCP is the default.
- stop trying to detect:
   - use dlm.conf to switch from TCP to SCTP.
   - corosync.conf 'rrp_mode' is not supported in corosync 2.x.
- TCP can work with multi-link, but only accept the first ip addr from corosync.
- SCTP can support max 8 ip addr for corosync 3.x.

If there are no further discussions, I will provide a patch.

- Heming