Re: [PATCH v2] hw/uefi: add "info ovmf-log" + "query-ovmf-log" monitor commands

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Oct 09, 2025 at 01:56:09AM +0000, Dr. David Alan Gilbert wrote:
> * Gerd Hoffmann (kraxel@redhat.com) wrote:
> > Starting with the edk2-stable202508 tag OVMF (and ArmVirt too) have
> > optional support for logging to a memory buffer.  There is guest side
> > support -- for example in linux kernels v6.17+ -- to read that buffer.
> > But that might not helpful if your guest stops booting early enough that
> > guest tooling can not be used yet.  So host side support to read that
> > log buffer is a useful thing to have.
> > 
> > This patch implements both qmp and hmp monitor commands to read the
> > firmware log.
> > 
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> 
> I'm OK with that, but I wonder if it would be better to have a command
> that wrote the buffer to a file rather than displaying it directly; I don't
> think we normally have anything else which outputs that much raw guest
> provided data directly.
> I assume when it goes wrong you end up with random unprintable junk in
> the buffer.

128 KB is on the high side, but is not terrible. Libvirt (arbitrarily)
caps a QMP reply at 10 MB. Libvirt is going to want to send this on to
the client app and will likely do that streaming in memory, so having
it iin a file is not required from our POV.

IIRC, some of the query-block command replies can get insanely huge
when the qcow2 chain is very long.

With regards,
Daniel
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