Re: [Qemu-devel] PC machine types switched to SeaBIOS/gPXE

[Avi Kivity <avi@redhat.com>]

On 11/03/2009 06:57 AM, Alexander Graf wrote:
>> Yes, I'd prefer to see this.  In earlier emails, Gleb made a reference
>> to a qemu-cfg "stream" interface that is used for acpi tables - maybe
>> the kernel could be put in one of the streams and the rom could copy
>> it into ram on boot.
>
>
> I don't think streaming is the right approach here. Streaming would 
> mean the rom had to copy, which again either a lot of PIO accesses 
> (slow!) or a complicated DMA interface.

A rep/ins instruction will take one exit/page so it won't be 
particularly slow.

> I'd rather go for a RAM poking approach. As soon as the option rom is 
> loaded, it calls qemu via PIO telling it to "load the kernel in RAM 
> now" and as of the next instruction everything's in place at the 
> determined addresses. It's not like we could do anything about the 
> physical layout in the option rom anyways, usually the kernel tells us 
> what that looks like.

That works too, but if firmware config can use rep/ins, that's one less 
interface we have to add.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.