Re: [PATCH 0/3] target: RFC: display deprecation note for '-cpu help'

[Daniel P . Berrangé]

On Mon, Jul 18, 2022 at 11:37:35AM +0200, Cornelia Huck wrote:
> On Mon, Jul 18 2022, Thomas Huth <thuth@redhat.com> wrote:
> 
> > On 14/07/2022 17.07, Daniel P. Berrangé wrote:
> >> $ qemu-system-x86_64 -cpu help:
> >> Available CPUs:
> >> x86 486                   (alias configured by machine type) (deprecated: 
> >> use at least 'Nehalem' / 'Opteron_G4', or 'host' / 'max')
> >> 
> >> I wonder if this is too verbose, and we should just do a
> >> concise flag like approach, similar to QMP:
> >> 
> >> $ qemu-system-x86_64 -cpu help:
> >> Available CPUs:
> >> x86 486                   (alias configured by machine type) (deprecated)
> >> 
> >> leaving the full message to be displayed at runtime ? I'm slightly
> >> inclined to the simpler more concise output.
> >
> > I'd prefer to keep it short here and just write "deprecated" without the 
> > reason. Otherwise this will overflow the lines and break the readability of 
> > the output. And it's also what we're also doing for "-machine", e.g.:
> >
> > $ ./qemu-system-ppc64 -M help | grep deprecate
> > taihu                taihu (deprecated)
> > $ ./qemu-system-ppc64 -M taihu
> > qemu-system-ppc64: warning: Machine type 'taihu' is deprecated: incomplete, 
> > use 'ref405ep' instead
> 
> Ok, following what -machine does is certainly a good point.

Yes, I should have thought to check what -machine does, it makese
sense to be consistent.

> Is it easy enough the figure out the deprecation note? I think you
> either have to actually start something with the deprecated entity, or
> use qmp (which is not that straightforward)?

QMP doesn't tell you the note, just a boolean deprecation flag. It is
only printed on startup only right now.

In the context of libvirt what happens is that libvirt can report that
something is deprecated (based on the QMP response). If you go ahead
and use it anyway, you'll get the deprecation message in the logfile
for the VM, and the VM gets marked tainted by libvirt, which serves
as a guide to look in the logfile.

With regards,
Daniel
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