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

[Ka-Cheong Poon <ka-cheong.poon@oracle.com>]

On 10/6/20 8:46 PM, Jason Gunthorpe wrote:
> On Tue, Oct 06, 2020 at 05:36:32PM +0800, Ka-Cheong Poon wrote:
> 
>>>>> Kernel modules should not be doing networking unless commanded to by
>>>>> userspace.
>>>>
>>>> It is still not clear why this is an issue with RDMA
>>>> connection, but not with general kernel socket.  It is
>>>> not random networking.  There is a purpose.
>>>
>>> It is a problem with sockets too, how do the socket users trigger
>>> their socket usages? AFAIK all cases originate with userspace
>>
>> A user starts a namespace.  The module is loaded for servicing
>> requests.  The module starts a listener.  The user deletes
>> the namespace.  This scenario will have everything cleaned up
>> properly if the listener is a kernel socket.  This is not the
>> case with RDMA.
> 
> Please point to reputable code in upstream doing this


It is not clear what "reputable" here really means.  If it just
means something in kernel, then nearly all, if not all, Internet
protocols code in kernel create a control kernel socket for every
network namespaces.  That socket is deleted in the per namespace
exit function.  If it explicitly means listening socket, AFS and
TIPC in kernel do that for every namespaces.  That socket is
deleted in the per namespace exit function.

It is very common for a network protocol to have something like
this for protocol processing.  It is not clear why RDMA subsystem
behaves differently and forbids this common practice.  Could you
please elaborate the issues this practice has such that the RDMA
subsystem cannot support it?



-- 
K. Poon
ka-cheong.poon@oracle.com