Re: [Qemu-devel] [PATCH] turn firmware image filename into a machine option

[Peter Maydell]

On 1 October 2013 21:16, Gerd Hoffmann <address@hidden> wrote:
>   Hi,
>
>> -bios we're stuck with because it's a legacy
>> option,
>
> What is legacy about it?

The fact that we've had it since forever, it was introduced for
a specific x86 use case and has since accreted behaviour
rather than being designed.

>> >> Why is this a machine option rather than a property of
>> >> the ROM/flash device?
>> >
>> > Not all machines have a flash device.
>>
>> No, but they must have *something* that the firmware code lives in...
>
> Some don't.  They just memcpy the firmware into guest ram instead.

...is that a good thing? What does the real hardware do? Should we
be doing that instead? Isn't this awkward on reset?

>> > Also flash drives don't want a
>> > simple (readonly) image file but a (writable) blockdev as backing
>> > storage, at least the pflash device emulation I've briefly looked at.
>>
>> ...so how does this work for machines where the firmware lives in
>> a flash device?
>
> pc: In case '-pflash $blockdev' is present '-bios $image' is ignored.
>
> My patch doesn't change that behavior, i.e. -machine firmware=$image is
> ignored too in case -plflash is present on the command line.
>
> Given that pflash operates on a blockdev I don't see a obvious way to
> change that ...

We could make pflash accept a plain file which is then used as the
read-only initialization for a blockdev which isn't backed by anything,
for example. That would be useful for other pflash usage scenarios
too.

-- PMM