Re: RDMA subsystem namespace related questions (was Re: Finding the namespace of a struct ib_device)

[Chuck Lever <chucklever@gmail.com>]

> On Oct 9, 2020, at 11:34 AM, Jason Gunthorpe <jgg@ziepe.ca> wrote:
> 
> On Fri, Oct 09, 2020 at 11:27:44AM -0400, Chuck Lever wrote:
> 
>> Therefore I think the approach is going to be "one RDS listener per
>> net namespace". The problem Ka-Cheong is trying to address is how to
>> manage the destruction of a listener-namespace pair. The extra
>> reference count on the cm_id is pinning the namespace so it cannot
>> be destroyed.
> 
> I really don't think this idea of just loading a kernel module and it
> immediately creates a network visibile listening socket in every
> namespace is very good.
> 
>> Understood, but it doesn't seem like there is enough useful overlap
>> between the NFS and RDS usage scenarios. With NFS, I would expect
>> an explicit listener shutdown from userland prior to namespace
>> destruction.
> 
> Yes, because namespaces are fundamentally supposed to be anchored in
> the processes inside the namespace.

Aye, the container model.


> Having the kernel jump in and start opening holes as soon as a
> namespace is created is just wrong.
> 
> At a bare minimum the listener should not exist until something in the
> namespace is willing to work with RDS.

I was thinking that too, but I'm not sure if that change would have
ramifications to existing RDS applications. There's quite a bit of
legacy to deal with.

An alternative would be to add a user daemon to RDS to manage the
listener lifecycle, rather than having the endpoint created by
module load. That might help the listener-namespace destruction
issue, and should be entirely application-transparent.


--
Chuck Lever
chucklever@gmail.com