Re: [Qemu-devel] [PATCH v3] vl.c: Output error on invalid machine type provided

[Eric Blake <eblake@redhat.com>]

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On 07/30/2013 01:10 PM, Michal Novotny wrote:
> Output error message when user provides the invalid machine type
> on the command line. This also saves time to find what issue is
> when you upgrade from one version of qemu to another version that
> doesn't support required machine type any longer.

I know that has historically happened downstream (for example, Fedora 13
made the mistake of creating a downstream-only fedora-13 machine type
that corresponded roughly to qemu 0.13, it took some further Fedora
patches to libvirt to modernize that name back to an upstream machine
type on an upgrade path before finally being able to drop the downstream
nonsense in Fedora 18 or so).  But isn't upstream qemu supposed to be
guaranteeing command-line stability, in that a newer qemu will never
take away a machine type supported by an older qemu?

But even if the upstream upgrade path never hits this code, your patch
will make it nicer if you _downgrade_ to a version of qemu (still with
this patch, of course) that lacks support for a newer machine.  And the
fact that downstream will take advantage of this even if upstream never
causes the problem on upgrades still justifies using it.

> 
> Signed-off-by: Michal Novotny <minovotn@redhat.com>
> 
> ---
> The patch is checked using ./scripts/checkpatch.pl script and
> also is_help_option() function is being used.
>  vl.c | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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