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Re: [libvirt] [PATCH] virDomainNetDefCheckABIStability: Check for MTU change too



On Thu, Aug 30, 2018 at 02:14:27PM +0200, Michal Privoznik wrote:
> https://bugzilla.redhat.com/show_bug.cgi?id=1623157
> 
> Changing MTU on a running guest is not possible and trying to do
> so made us face many problems. That's why we forbid it in
> 5f44d7e357f61f7. However, there is still one possible path where
> users can sneak in change: migration XML.
> 
> Signed-off-by: Michal Privoznik <mprivozn redhat com>
> ---
>  src/conf/domain_conf.c | 7 +++++++
>  1 file changed, 7 insertions(+)

Reviewed-by: Daniel P. Berrangé <berrange redhat com>


> 
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 38cac07913..59ca9f5888 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -21901,6 +21901,13 @@ virDomainNetDefCheckABIStability(virDomainNetDefPtr src,
>          return false;
>      }
>  
> +    if (src->mtu != dst->mtu) {
> +        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> +                       _("Target network card MTU %d does not match source %d"),
> +                       dst->mtu, src->mtu);
> +        return false;
> +    }
> +
>      if (src->virtio && dst->virtio &&
>          !virDomainVirtioOptionsCheckABIStability(src->virtio, dst->virtio))
>          return false;

The virDomainNetDefCheckABIStability function feels like it need more
work to it, so I'm not convinced it is safe to change the def->driver.*
fields either - especially number of queues. That can be dealy with
separately though.

Regards,
Daniel
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