Re: [libvirt] [PATCH] Don't parse/format vram attribute for cirrus video
On Fri, 2019-06-21 at 08:13 +0200, Peter Krempa wrote:
On Thu, Jun 20, 2019 at 14:51:12 -0500, Jonathon Jongsma wrote:
> Since the cirrus vga memory size isn't configurable, we can ignore
> any
> 'vram' attribute when parsing a domain definition. However, when no
> value is specified, it ends up getting set to a default value of
> 16MB.
> This 16MB value is not used anywhere (for example, it is not passed
> as
> an argument to qemu), but is displayed in the XML definition. So by
> changing this default value to 0, it will also be omitted from the
> XML
> definition of the domain.
>
> Fixes: rhbz#1447831
Please always use the full link so that it's clickable and users
don't
have to figure out what 'rhbz' is.
> Signed-off-by: Jonathon Jongsma <jjongsma(a)redhat.com>
> ---
> This is an attempt to apply the fix suggested by Gerd at
> https://bugzilla.redhat.com/show_bug.cgi?id=1447831#c2. I'm not
> totally confident that this is the right approach, since I'm
> relatively new to the code. Another approach might be to simply
> close
> the bug as NOTABUG since it doesn't seem that having this unused
> attribute in the domain definition has any significant drawbacks.
We certainly should not set any default if it's not used. There's not
much else we can do though as we did put a default into the
configuration.
I'm not sure I understand what you're suggesting here. This sentence
seems to imply that you think we should *not* set a default, but down
below you say that you're not certain whether we should clear the
default? It seems a bit contradictory, but perhaps I'm simply
misunderstanding.
Doing any validation would mean that any VM which had the
default errorneously configured in the XML would fail to start.
Yeah, I did not do any 'validation' of cirrus vram attributes because I
didn't want existing VMs to fail to start. And all existing VMs that
use the cirrus device presumably have this attribute set in their XML
definition. So I simply ignored this parameter rather than rejecting
it. But as I said, I'm not sure whether that's the correct approach for
libvirt.
Whether it's worth clearing the default or not I'm not so certain but
I
don't think it should hurt.
You definitely should fix the docs though:
https://libvirt.org/formatdomain.html#elementsVideo
As it says 'For a guest of type "kvm", the default video is: type
with
value "cirrus", vram with value "16384" and heads with value
"1".'
(see docs/formatdomain.html.in )
Thanks, will do.
Jonathon