Re: About creating machines on the command line

[Alexander Graf]

On 05.02.21 11:43, Luc Michel wrote:
> On 2/3/21 6:09 PM, Alexander Graf wrote:
> > On 03.02.21 17:55, Philippe Mathieu-Daudé wrote:
> > > On 1/11/21 3:50 PM, Luc Michel wrote:
> > > > Hi,
> > > >
> > > > We would like to work on improving QEMU to be able to create custom
> > > > machines from the command line. The goal here is to get feedback from
> > > > the community and shape the future developments.
> > >
> > > Cc'ing John who is working on command line, and some developers from
> > > the "inter-VM device emulation interface" call.
> > > https://www.mail-archive.com/qemu-devel@nongnu.org/msg723252.html
> > >
> > > > The use case mainly comes from people working with tools to customize
> > > > their designs, such as SiFive Core Designer
> > > > (https://scs.sifive.com/core-designer). This kind of tools may allow
> > > > creation or customization of a whole SoC, from the number of cores, to
> > > > the memory and IRQ mapping of peripherals etc.
> > > >
> > > > The ultimate goal would be to be able to create any kind of machine on
> > > > the command line. However we are aware that this is a substantial 
> > > > amount
> > > > of changes in QEMU.
> >
> > Is the command line really the right abstraction level here? Wouldn't it
> > make more sense to have a QOM / <scripting language> bridge that allows
> > you to create and connect QOM objects using for example Python?
> Yes, after some discussions with the community, we are now working on
> improving QMP to achieve this. We first started with the idea of the
> command line because it seems to be the place where we had "almost"
> everything we needed already. In either cases we are planning to use a
> front-end script to go from e.g. a DTB to whatever QEMU interface we
> will end up using.
>
> > You could then have machine descriptions in a script, which could be
> > generated by the SoC customization tools.
> Yes, most likely a DTB in our case.

So, something like this?

    https://github.com/Xilinx/qemu/blob/master/hw/arm/arm_generic_fdt.c

I'm not sure how DTB would translate 1:1 into qom properties for a reeal 
generic mechanism? And how easy it would be to extract target device 
specifics, such as interrupt descriptors or PCI ranges properties.

If you want to make this fully generic, try to ensure that you can model 
weird beasts such as the q35 machine model.

Either way, the idea has come up multiple times before. I don't know of 
anyone who successfully managed to push it upstream yet, but I 
definitely hope we will be at a point where you can describe machine 
models in something different than C.


Alex



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