[Qemu-devel] Re: [PATCH] Snapshot block device support

[Fabrice Bellard]

Rusty Russell wrote:
> In message <address@hidden> you write:
>
> > I tested with 2.5.74 and fixed the initial IDE error. I also added the
> > emulation of the PC 'reset' pin so that vl can be shut down as a normal 
> > Linux system (only hard reset is supported, not power off, as it would 
> > require a more complicated real mode APM bios emulation).
>
>
> I know someone who might be interested: I'll ask tomorrow.

OK.

> > Now I am looking for potential original uses of vl/QEMU !
>
>
> Hmm, what are the chances of SMP?  You mentioned something about it
> probing addresses you couldn't map, perhaps another job for
> CONFIG_QEMU inside the kernel, or is it too invasive?
>
> Even with only one CPU, it helps my debugging to be able to test
> CONFIG_SMP=y...

I realize that SMP simulation can be interesting. I could at least learn 
how it works as I never looked at it. The simplest solution would be to 
use CONFIG_QEMU to change the FIXADDR_TOP address in fixmap.h (I am 
going to test that). I have looked at APIC and IOAPIC simulation in 
bochs and it does not seem so complicated. My real problem is how to 
simulate several CPUs at the same time. A solution is to use a single 
process and to schedule by hand. It is costly because the address space 
must be switched between each CPU. Another solution is to use separate 
processes, but it complicates the hardware simulation. Any ideas ?

Fabrice.