Re: [Xen-devel] [Qemu-devel] Project idea: make QEMU more flexible

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Jan 06, 2014 at 11:23:24PM +1000, Peter Crosthwaite wrote:
[...]
> >
> > Down to implementation level I only need to (hopefully) add a few stubs
> > and create some new CONFIG_* options and move a few things around. It
> > might not be as intrusive as one thinks.
> >
> > In fact I've already hacked a prototype during Christmas. What's I've
> > done so far:
> >
> > 1. create target-null which only has some stubs to CPU emulation
> >    framework.
> >
> > 2. add a few lines to configure / Makefiles*, create
> >    default-configs/null-softmmu
> >
> 
> Your idea of aggressively reducing binary size may not really fit a
> defconfig at all. If you are going lean-and-mean based on a specific
> use-case I think you need to bring your own config.
> 

Fair enough.

> > Finally I got a qemu-system-null. And the effect is immediately visible
> 
> qemu-system-null has been on my wish-list in the past, although my
> reasons were slightly different to yours. Specifically, the goal was
> to test CPUs in an RTL simulator interacting with RAM and peripheral
> devices hosted in QEMU.
> 

Cool. However small this is still a valid usecase.

> > -- the size of QEMU binary shrinked from 13MB to 7.6MB. I haven't really
> > looked at what device emulation code can be removed so the size can even
> > be made smaller.
> >
> 
> So what exactly is an appropriate device-suite for qemu-system-null is
> an open question. I would suggest that the "correct" default config
> for such a QEMU would actually be the full suite of devices, not less
> that whats already in i386. Free of CPU/arch restrictions, all devices
> are fair game.
> 

Good point. So only avoid the CPU emulation code and leave full device
emulations alone. Will this make a sensible defconfig? ;-)

Wei.

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