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

[Klaus Birkelund <klaus@birkelund.eu>]

On Tue, Jun 25, 2019 at 07:51:29AM +0200, Markus Armbruster wrote:
> Laszlo Ersek <lersek@redhat.com> writes:
> 
> > On 06/24/19 12:18, Kevin Wolf wrote:
> >> 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.
> 
> Devices can be wired together without a bus intermediary.  You
> definitely want a bus when the physical connection you model has one.
> If not, a bus may be useful anyway, say because it provides a convenient
> way to encapsulate the connection model, or to support -device bus=...
> 
 
I'm not sure how to wire it together without the bus abstraction? So
I'll stick with the bus for now. It *is* extremely convenient!

Cheers,
Klaus