Re: [Qemu-devel] [Qemu-block] [PATCH 16/16] nvme: support multiple namespaces

[Klaus Birkelund]

On Fri, Jul 05, 2019 at 02:49:29PM +0100, Daniel P. Berrangé wrote:
> On Fri, Jul 05, 2019 at 03:36:17PM +0200, Klaus Birkelund wrote:
> > On Fri, Jul 05, 2019 at 09:23:33AM +0200, Klaus Birkelund Jensen wrote:
> > > This adds support for multiple namespaces by introducing a new 'nvme-ns'
> > > device model. The nvme device creates a bus named from the device name
> > > ('id'). The nvme-ns devices then connect to this and registers
> > > themselves with the nvme device.
> > > 
> > > This changes how an nvme device is created. Example with two namespaces:
> > > 
> > >   -drive file=nvme0n1.img,if=none,id=disk1
> > >   -drive file=nvme0n2.img,if=none,id=disk2
> > >   -device nvme,serial=deadbeef,id=nvme0
> > >   -device nvme-ns,drive=disk1,bus=nvme0,nsid=1
> > >   -device nvme-ns,drive=disk2,bus=nvme0,nsid=2
> > > 
> > > A maximum of 256 namespaces can be configured.
> > > 
> >  
> > Well that was embarrasing.
> > 
> > This patch breaks nvme-test.c. Which I obviously did not run.
> > 
> > In my defense, the test doesn't do much currently, but I'll of course
> > fix the test for v2.
> 
> That highlights a more serious problem.  This series changes the syntx
> for configuring the nvme device in a way that is not backwards compatible.
> So anyone who is using QEMU with NVME will be broken when they upgrade
> to the next QEMU release.
> 
> I understand why you wanted to restructure things to have a separate
> nvme-ns device, but there needs to be some backcompat support in there
> for the existing syntax to avoid breaking current users IMHO.
> 
 
Hi Daniel,

I raised this issue previously. I suggested that we keep the drive
property for the nvme device and only accept either that or an nvme-ns
device to be configured (but not both).

That would keep backward compatibilty, but enforce the use of nvme-ns
for any setup that requires multiple namespaces.

Would that work?

Cheers,
Klaus