Re: [Qemu-devel] [RFC virt-spec PATCH] only writing out the last byte of MAC makes it have effect

[Michael S. Tsirkin]

On Thu, Mar 21, 2013 at 11:02:36AM +0800, Amos Kong wrote:
> The lengcy guests don't have mac programming command, we don't know when
> it's safe to use MAC. We can change QEMU to make MAC change effect when
> the last byte of MAC is written to config space.
> 
> Signed-off-by: Amos Kong <address@hidden>
> ---
>  virtio-spec.lyx | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/virtio-spec.lyx b/virtio-spec.lyx
> index dbc4ef0..bb289fb 100644
> --- a/virtio-spec.lyx
> +++ b/virtio-spec.lyx
> @@ -5430,7 +5430,7 @@ T_CTRL_MAC_TABLE_SET.
>  
>  \begin_layout Standard
>  
> -\change_inserted -1930653948 1358506710
> +\change_inserted -1930653948 1363832689
>  The config space 
>  \begin_inset Quotes eld
>  \end_inset
> @@ -5464,6 +5464,15 @@ mac
>   Therefore, VIRTIO_NET_CTRL_MAC_ADDR_SET is preferred, especially while
>   the NIC is up.
>   The command-specific-data is a 6-byte MAC address.
> +\end_layout
> +
> +\begin_layout Standard
> +
> +\change_inserted -1930653948 1363833477
> +The legacy guests don't support the new command, they still change MAC 
> address
> + in original way, that's not atomic.
> + For more robust, QEMU only makes the MAC change effect when the last byte
> + of MAC address is written to config space.
>  \change_unchanged
>  
>  \end_layout

The wording can be improved, but before that - Rusty, what
do you think about such a hack? Worth supporting or
let's just ask everyone to update drivers?

> -- 
> 1.8.1.4