Re: [Qemu-devel] [Qemu-block] [RFC] nvme: how to support multiple namespaces

[Kevin Wolf <kwolf@redhat.com>]

Am 24.06.2019 um 10:01 hat Klaus Birkelund geschrieben:
> On Thu, Jun 20, 2019 at 05:37:24PM +0200, Laszlo Ersek wrote:
> > On 06/17/19 10:12, Klaus Birkelund wrote:
> > > Hi all,
> > > 
> > > I'm thinking about how to support multiple namespaces in the NVMe
> > > device. My first idea was to add a "namespaces" property array to the
> > > device that references blockdevs, but as Laszlo writes below, this might
> > > not be the best idea. It also makes it troublesome to add per-namespace
> > > parameters (which is something I will be required to do for other
> > > reasons). Some of you might remember my first attempt at this that
> > > included adding a new block driver (derived from raw) that could be
> > > given certain parameters that would then be stored in the image. But I
> > > understand that this is a no-go, and I can see why.
> > > 
> > > I guess the optimal way would be such that the parameters was something
> > > like:
> > > 
> > >    -blockdev raw,node-name=blk_ns1,file.driver=file,file.filename=blk_ns1.img
> > >    -blockdev raw,node-name=blk_ns2,file.driver=file,file.filename=blk_ns2.img
> > >    -device nvme-ns,drive=blk_ns1,ns-specific-options (nsfeat,mc,dlfeat)...
> > >    -device nvme-ns,drive=blk_ns2,...
> > >    -device nvme,...
> > > 
> > > My question is how to state the parent/child relationship between the
> > > nvme and nvme-ns devices. I've been looking at how ide and virtio does
> > > this, and maybe a "bus" is the right way to go?
> > 
> > I've added Markus to the address list, because of this question. No
> > other (new) comments from me on the thread starter at this time, just
> > keeping the full context.
> > 
> 
> Hi all,
> 
> I've succesfully implemented this by introducing a new 'nvme-ns' device
> model. The nvme device creates a bus named from the device id ('id'
> parameter) and the nvme-ns devices are then registered on this.
> 
> This results in an nvme device being creates like this (two namespaces
> example):
> 
>   -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
> 
> How does that look as a way forward?

This looks very similar to what other devices do (one bus controller
that has multiple devices on its but), so I like it.

The thing that is special here is that -device nvme is already a block
device by itself that can take a drive property. So how does this play
together? Can I choose to either specify a drive directly for the nvme
device or nvme-ns devices, but when I do both, I will get an error? What
happens if I don't specify a drive for nvme, but also don't add nvme-ns
devices?

Kevin