[PATCH v2] docs: expand firmware descriptor to allow flash without NVRAM
kchamart at redhat.com
Mon Jan 31 15:58:31 UTC 2022
On Mon, Jan 31, 2022 at 03:35:02PM +0000, Daniel P. Berrangé wrote:
> 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:
> > > 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
I should've first checked the spec to look for the @format field. For
others reading the thread, the @format bit is located here
# Defines common properties that are necessary for loading a firmware
# file into a pflash chip. The corresponding QEMU command line option is
# "-drive file=@filename,format=@format". Note however that the
# option-argument shown here is incomplete; it is completed under
# @filename: Specifies the filename on the host filesystem where the
# firmware file can be found.
# @format: Specifies the block format of the file pointed-to by
# @filename, such as @raw or @qcow2.
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