Re: Finding the namespace of a struct ib_device

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

On 9/7/20 5:04 PM, Leon Romanovsky wrote:
> On Mon, Sep 07, 2020 at 04:24:26PM +0800, Ka-Cheong Poon wrote:
>> On 9/7/20 3:18 PM, Leon Romanovsky wrote:
>>> On Mon, Sep 07, 2020 at 11:33:38AM +0800, Ka-Cheong Poon wrote:
>>>> On 9/6/20 3:44 PM, Leon Romanovsky wrote:
>>>>> On Fri, Sep 04, 2020 at 10:02:10PM +0800, Ka-Cheong Poon wrote:
>>>>>> On 9/4/20 7:32 PM, Jason Gunthorpe wrote:
>>>>>>> On Fri, Sep 04, 2020 at 12:01:12PM +0800, Ka-Cheong Poon wrote:
>>>>>>>> On 9/4/20 1:39 AM, Jason Gunthorpe wrote:
>>>>>>>>> On Thu, Sep 03, 2020 at 10:02:01PM +0800, Ka-Cheong Poon wrote:
>>>>>>>>>> When a struct ib_client's add() function is called. is there a
>>>>>>>>>> supported method to find out the namespace of the passed in
>>>>>>>>>> struct ib_device?  There is rdma_dev_access_netns() but it does
>>>>>>>>>> not return the namespace.  It seems that it needs to have
>>>>>>>>>> something like the following.
>>>>>>>>>>
>>>>>>>>>> struct net *rdma_dev_to_netns(struct ib_device *ib_dev)
>>>>>>>>>> {
>>>>>>>>>>             return read_pnet(&ib_dev->coredev.rdma_net);
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> Comments?
>>>>>>>>>
>>>>>>>>> I suppose, but why would something need this?
>>>>>>>>
>>>>>>>>
>>>>>>>> If the client needs to allocate stuff for the namespace
>>>>>>>> related to that device, it needs to know the namespace of
>>>>>>>> that device.  Then when that namespace is deleted, the
>>>>>>>> client can clean up those related stuff as the client's
>>>>>>>> namespace exit function can be called before the remove()
>>>>>>>> function is triggered in rdma_dev_exit_net().  Without
>>>>>>>> knowing the namespace of that device, coordination cannot
>>>>>>>> be done.
>>>>>>>
>>>>>>> Since each device can only be in one namespace, why would a client
>>>>>>> ever need to allocate at a level more granular than a device?
>>>>>>
>>>>>>
>>>>>> A client wants to have namespace specific info.  If the
>>>>>> device belongs to a namespace, it wants to associate those
>>>>>> info with that device.  When a namespace is deleted, the
>>>>>> info will need to be deleted.  You can consider the info
>>>>>> as associated with both a namespace and a device.
>>>>>
>>>>> Can you be more specific about which info you are talking about?
>>>>
>>>>
>>>> Actually, a lot of info can be both namespace and device specific.
>>>> For example, a client wants to have a different PD allocation policy
>>>> with a device when used in different namespaces.
>>>>
>>>>
>>>>> And what is the client that is net namespace-aware from one side,
>>>>> but from another separate data between them "manually"?
>>>>
>>>>
>>>> Could you please elaborate what is meant by "namespace aware from
>>>> one side but from another separate data between them manually"?
>>>> I understand what namespace aware means.  But it is not clear what
>>>> is meant by "separating data manually".  Do you mean having different
>>>> behavior in different namespaces?  If this is the case, there is
>>>> nothing special here.  An admin may choose to have different behavior
>>>> in different namespaces.  There is nothing manual going on in the
>>>> client code.
>>>
>>> We are talking about net-namespaces, and as we wrote above, the ib_device
>>> that supports such namespace can exist only in a single one
>>>
>>> The client that implemented such support can check its namespace while
>>> "client->add" is called. It should be equal to be seen by ib_device.
>>>
>>> See:
>>>    rdma_dev_change_netns ->
>>>    	enable_device_and_get ->
>>> 		add_client_context ->
>>> 			client->add(device)
>>
>>
>> This is the original question.  How does the client's add() function
>> know the namespace of device?  What is your suggestion in finding
>> the net namespace of device at add() time?
> 
> As I wrote above, "It should be equal to be seen by ib_device.", check net
> namespace of your client.


Could you please be more specific?  A client calls ib_register_client() to
register with the RDMA framework.  Then when a device is added, the client's
add() function is called with the struct ib_device.  How does the client
find out the namespace "seen by the ib_device"?  Do you mean that there is
a variant of ib_register_client() which can take a net namespace as parameter?
Or is there a variant of struct ib_client which has a net namespace field?
Or?  Thanks.


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