[PATCH v2] docs: expand firmware descriptor to allow flash without NVRAM

[Daniel P. Berrangé]

On Mon, Jan 31, 2022 at 04:21:36PM +0100, Kashyap Chamarthy wrote:
> On Mon, Jan 31, 2022 at 02:36:46PM +0000, Daniel P. Berrangé wrote:
> > On Mon, Jan 31, 2022 at 03:00:33PM +0100, Kashyap Chamarthy wrote:
> > > On Mon, Jan 31, 2022 at 12:55:09PM +0000, Daniel P. Berrangé wrote:
> 
> [...]
> 
> > > I briefly wondered if in this "combined" mode whether the no. of
> > > duplicate copies can ever fill up the storage.  I doubt that, as the
> > > combined size of _VARS + _CODE is just about 2MB.  So it only starts
> > > mattering if you're running tens of thousands of guests.
> > 
> > When guest root / data disk sizes are measured in 100's of MB, or
> > GBs, I struggle to get worried about even a 16 MB OVMF  blob being
> > copied per guest.
> 
> Heh, fair enough.
> 
> > The firmware can be provided in qcow2 format too, so if really
> > concerned, just create a qcow2 file with a backing store pointing
> > to the readonly master, so you're only paying the price of the
> > delta for any guest VARs writes. That's more efficient than what
> > we do today with copying the separate raw format VARS.fd file.
> 
> That's nice, I didn't know the qcow2 possibility in this context.  For
> some reason I assumed the file format always has to be raw here.  Your
> qcow2 point above should  be documented, if it isn't already.  Although
> I don't know the right place for it.

There's already a format field in the descriptor, but even if the
firmware is distributed as raw, libvirt can choose to put qcow2
overlay on it, as its all configured with -blockdev

Regards,
Daniel
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