Re: [RFC net-next 0/8] Introducing subdev bus and devlink extension

[Jakub Kicinski]

On Mon, 7 Jun 2021 09:36:38 +0800 Yunsheng Lin wrote:
> On 2021/6/5 2:41, Jakub Kicinski wrote:
> > On Fri, 4 Jun 2021 09:18:04 +0800 Yunsheng Lin wrote:  
> >> My initial thinking is a id from a global IDA pool, which indeed may
> >> change on every boot.
> >>
> >> I am not really thinking much deeper about the controller id, just
> >> mirroring the bus identifiers for pcie device and ifindex for netdev,  
> > 
> > devlink instance id seems fine, but there's already a controller
> > concept in devlink so please steer clear of that naming.  
> I am not sure if controller concept already existed is reusable for
> the devlink instance representing problem for multi-function which
> shares common resource in the same ASIC. If not, we do need to pick
> up other name.
> 
> Another thing I am not really think throught is how is the VF represented
> by the devlink instance when VF is passed through to a VM.
> I was thinking about VF is represented as devlink port, just like PF(with
> different port flavour), and VF devlink port only exist on the same host
> as PF(which assumes PF is never passed through to a VM), so it may means
> the PF is responsible for creating the devlink port for VF when VF is passed
> through to a VM?
> 
> Or do we need to create a devlink instance for VF in the VM too when the
> VF is passed through to a VM? Or more specificly, does user need to query
> or configure devlink info or configuration in a VM? If not, then devlink
> instance in VM seems unnecessary?

I believe the current best practice is to create a devlink instance for
the VF with a devlink port of type "virtual". Such instance represents
a "virtualized" view of the device.

> >> which may change too if the device is pluged into different pci slot
> >> on every boot?  
> > 
> > Heh. What is someone reflashes the part to change it's serial number? :)
> > pci slot is reasonably stable, as proven by years of experience trying
> > to find stable naming for netdevs.  
> 
> I suppose that requires a booting to take effect and a vendor tool
> to reflash the serial number, it seems reasonable the vendor/user will
> try their best to not mess the serial number, otherwise service and
> maintenance based on serial number will not work?
> I was thinking about adding the vendor name besides the serial number
> to indicate a devlink instance, to avoid that case that two hw from
> different vendor having the same serial number accidentally.

I'm not opposed to the use of attributes such as serial number for
selecting instance, in principle. I was just trying to prove that PCI
slot/PCI device name is as stable as any other attribute. 

In fact for mass-produced machines using PCI slot is far more
convenient than globally unique identifiers because it can be used 
to talk to a specific device in a server for all machines of a given
model, hence easing automation.

> >> We could still allow devlink instances to have multiple names,
> >> which seems to be more like devlink tool problem?
> >>
> >> For example, devlink tool could use the id or the vendor_info/
> >> serial_number to indicate a devlink instance according to user's
> >> request.  
> > 
> > Typing serial numbers seems pretty painful.
> >   
> >> Aliase could be allowed too as long as devlink core provide a
> >> field and ops to set/get the field mirroring the ifalias for
> >> netdevice?  
> > 
> > I don't understand.  
> 
> I meant we could still allow the user to provide a more meaningful
> name to indicate a devlink instance besides the id.

To clarify/summarize my statement above serial number may be a useful
addition but PCI device names should IMHO remain the primary
identifiers, even if it means devlink instances with multiple names.

In addition I don't think that user-controlled names/aliases are
necessarily a great idea for devlink.