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

Kashyap Chamarthy 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

Ah, understood.  

I should've first checked the spec to look for the @format field.  For
others reading the thread, the @format bit is located here

  # @FirmwareFlashFile:
  # 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
  # @FirmwareMappingFlash.
  # @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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