Re: [PATCH] nvme-core: Fix subsystem instance mismatches

[Keith Busch]

On Tue, Sep 03, 2019 at 10:08:01AM -0600, Logan Gunthorpe wrote:
> On 2019-08-31 9:29 a.m., Keith Busch wrote:
> > On Fri, Aug 30, 2019 at 06:01:39PM -0600, Logan Gunthorpe wrote:
> >> To fix this, assign the subsystem's instance based on the instance
> >> number of the controller's instance that first created it. There should
> >> always be fewer subsystems than controllers so the should not be a need
> >> to create extra subsystems that overlap existing controllers.
> > 
> > The subsystem's lifetime is not tied to the controller's. When the
> > controller is removed and releases its instance, the next controller
> > to take that available instance will create naming collisions with the
> > subsystem still using it.
> > 
> 
> Hmm, yes, ok.
> 
> So perhaps we can just make the subsystem prefer the ctrl's instance
> when allocating the ID? Then at least, in the common case, the
> controller numbers will match the subsystem numbers. Only when there's
> random hot-plugs would the numbers get out of sync.

I really don't know about a patch that works only on static
configurations. Connects and disconnects do happen on live systems,
so the numerals will inevitably get out of sync.

Could we possibly make /dev/nvmeX be a subsystem handle without causing
trouble for anyone? This would essentially be the same thing as today
for non-CMIC controllers with a device-per-controller and only affects
the CMIC ones.