Re: [PATCH for-next] RDMA/nldev: Add parent bdf to device information dump

[Gal Pressman <galpress@amazon.com>]

On 03/11/2020 16:22, Jason Gunthorpe wrote:
> On Tue, Nov 03, 2020 at 04:11:19PM +0200, Gal Pressman wrote:
>> On 03/11/2020 15:57, Leon Romanovsky wrote:
>>> On Tue, Nov 03, 2020 at 09:45:22AM -0400, Jason Gunthorpe wrote:
>>>> On Tue, Nov 03, 2020 at 03:26:27PM +0200, Gal Pressman wrote:
>>>>> Add the ability to query the device's bdf through rdma tool netlink
>>>>> command (in addition to the sysfs infra).
>>>>>
>>>>> In case of virtual devices (rxe/siw), the netdev bdf will be shown.
>>>>
>>>> Why? What is the use case?
>>>
>>> Right, and why isn't netdev (RDMA_NLDEV_ATTR_NDEV_NAME) enough?
>>
>> When taking system topology into consideration you need some way to pair the
>> ibdev and bdf, especially when working with multiple devices.
>> The netdev name doesn't exist on devices with no netdevs (IB, EFA).
> 
> You are supposed to use sysfs
> 
> /sys/class/infiniband/ibp0s9/device
> 
> Should always be the physical device
> 
>> Why rdma tool? Because it's more intuitive than sysfs.
> 
> But we generally don't put this information into netlink BDF is just
> the start, you need all the other topology information to make sense
> of it, and all that is in sysfs only already

As the commit message says, it's in addition to the device sysfs.

Many (if not most) of the existing rdma netlink commands are duplicates of some
sysfs entries, but show it in a more "modern" way.
I'm not convinced that bdf should be treated differently.

Similarly to how you can see netdevs bdf through 'ethtool -i' in addition to
sysfs, I think it's useful.