Re: [RFC PATCH 08/12] libxl: Q35 support (new option device_model_machine)

[Anthony PERARD <anthony.perard@citrix.com>]

On Wed, Mar 21, 2018 at 04:27:43PM +0000, Wei Liu wrote:
> On Tue, Mar 20, 2018 at 09:11:10AM +0000, Roger Pau Monné wrote:
> > On Tue, Mar 20, 2018 at 08:11:49AM +1000, Alexey G wrote:
> > > On Mon, 19 Mar 2018 17:01:18 +0000
> > > Roger Pau Monné <roger.pau@citrix.com> wrote:
> > > 
> > > >On Tue, Mar 13, 2018 at 04:33:53AM +1000, Alexey Gerasimenko wrote:
> > > >> Provide a new domain config option to select the emulated machine
> > > >> type, device_model_machine. It has following possible values:
> > > >> - "i440" - i440 emulation (default)
> > > >> - "q35" - emulate a Q35 machine. By default, the storage interface
> > > >> is AHCI.  
> > > >
> > > >I would rather name this machine_chipset or device_model_chipset.
> > > 
> > > device_model_ prefix is a must I think -- multiple device model related
> > > options have names starting with device_model_.
> > > 
> > > device_model_chipset... well, maybe, but we're actually specifying a
> > > QEMU machine here. In QEMU mailing list there was even a suggestion
> > > to allow to pass a machine version number here, like "pc-q35-2.10".
> > > I think some opinions are needed here.
> > 
> > I'm not sure what a 'machine' is in QEMU speak, but in my mind I would
> > consider PC a machine (vs ARM for example).
> > 
> > I think 'chipset' is clearer, but again others should express their
> > opinion.
> 
> AIUI machine is a collection of chipset and peripherals, i.e. it covers
> more than the chipset alone.

The description of the QEMU machine "q35" is
"Standard PC (Q35 + ICH9, 2009)". So right in the description, Q35 is
not enought to describe what -machine=q35 is about. And FYI "pc" or
"pc_piix" description is "Standard PC (i440FX + PIIX, 1996)".

Also, we could expand the option to actually allow a user to select the
exact version of the QEMU machine to use. Having "pc-i440fx-2.12" in
the xl config file instead of just "pc" could prevent compatibility
issue for an existing virtual machine.

I don't know what a chipset is when related to QEMU, beside being a
piece of silicon in hardware. I think a QEMU machine is closer to a
motherboard than just a chipset. Feel free to read
"qemu.git/hw/i386/pc_piix.c" and "qemu.git/hw/i386/pc_q35.c"
to read the difference between both machine.

Anyway, I think "device_model_machine" is better that ".._chipset".
"machine" better describe the change involve when selecting q35.

-- 
Anthony PERARD

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