Re: device compatibility interface for live migration with assigned devices

[Yan Zhao]

On Wed, Aug 19, 2020 at 09:22:34PM -0600, Alex Williamson wrote:
> On Thu, 20 Aug 2020 08:39:22 +0800
> Yan Zhao <yan.y.zhao@intel.com> wrote:
> 
> > On Tue, Aug 18, 2020 at 11:36:52AM +0200, Cornelia Huck wrote:
> > > On Tue, 18 Aug 2020 10:16:28 +0100
> > > Daniel P. Berrangé <berrange@redhat.com> wrote:
> > >   
> > > > On Tue, Aug 18, 2020 at 05:01:51PM +0800, Jason Wang wrote:  
> > > > >    On 2020/8/18 下午4:55, Daniel P. Berrangé wrote:
> > > > > 
> > > > >  On Tue, Aug 18, 2020 at 11:24:30AM +0800, Jason Wang wrote:
> > > > > 
> > > > >  On 2020/8/14 下午1:16, Yan Zhao wrote:
> > > > > 
> > > > >  On Thu, Aug 13, 2020 at 12:24:50PM +0800, Jason Wang wrote:
> > > > > 
> > > > >  On 2020/8/10 下午3:46, Yan Zhao wrote:    
> > > >   
> > > > >  we actually can also retrieve the same information through sysfs, 
> > > > > .e.g
> > > > > 
> > > > >  |- [path to device]
> > > > >     |--- migration
> > > > >     |     |--- self
> > > > >     |     |   |---device_api
> > > > >     |    |   |---mdev_type
> > > > >     |    |   |---software_version
> > > > >     |    |   |---device_id
> > > > >     |    |   |---aggregator
> > > > >     |     |--- compatible
> > > > >     |     |   |---device_api
> > > > >     |    |   |---mdev_type
> > > > >     |    |   |---software_version
> > > > >     |    |   |---device_id
> > > > >     |    |   |---aggregator
> > > > > 
> > > > > 
> > > > >  Yes but:
> > > > > 
> > > > >  - You need one file per attribute (one syscall for one attribute)
> > > > >  - Attribute is coupled with kobject  
> > > 
> > > Is that really that bad? You have the device with an embedded kobject
> > > anyway, and you can just put things into an attribute group?
> > > 
> > > [Also, I think that self/compatible split in the example makes things
> > > needlessly complex. Shouldn't semantic versioning and matching already
> > > cover nearly everything? I would expect very few cases that are more
> > > complex than that. Maybe the aggregation stuff, but I don't think we
> > > need that self/compatible split for that, either.]  
> > Hi Cornelia,
> > 
> > The reason I want to declare compatible list of attributes is that
> > sometimes it's not a simple 1:1 matching of source attributes and target 
> > attributes
> > as I demonstrated below,
> > source mdev of (mdev_type i915-GVTg_V5_2 + aggregator 1) is compatible to
> > target mdev of (mdev_type i915-GVTg_V5_4 + aggregator 2),
> >                (mdev_type i915-GVTg_V5_8 + aggregator 4)
> > 
> > and aggragator may be just one of such examples that 1:1 matching does not
> > fit.
> 
> If you're suggesting that we need a new 'compatible' set for every
> aggregation, haven't we lost the purpose of aggregation?  For example,
> rather than having N mdev types to represent all the possible
> aggregation values, we have a single mdev type with N compatible
> migration entries, one for each possible aggregation value.  BTW, how do
> we have multiple compatible directories?  compatible0001,
> compatible0002? Thanks,
> 
do you think the bin_attribute I proposed yesterday good?
Then we can have a single compatible with a variable in the mdev_type and
aggregator.

   mdev_type=i915-GVTg_V5_{val1:int:2,4,8}
   aggregator={val1}/2

Thanks
Yan