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Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC
From: |
Rusty Russell |
Subject: |
Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect |
Date: |
Fri, 22 Mar 2013 10:45:09 +1030 |
User-agent: |
Notmuch/0.14 (http://notmuchmail.org) Emacs/23.4.1 (i686-pc-linux-gnu) |
"Michael S. Tsirkin" <address@hidden> writes:
> On Thu, Mar 21, 2013 at 02:44:50PM +0800, Amos Kong wrote:
>> The lengcy guests don't have mac programming command, we don't know when
>> it's safe to use MAC. This patch changed qemu to makes MAC change effect
>> when the last byte of MAC is written to config space.
>>
>> MAC address takes first 6 bytes of config space of virtio-net, the addr
>> is 5 when the last byte is written in virtio_config_writeb().
>>
>> MAC change will effect when n->mac is updated in virtio_net_set_config().
>>
>> Signed-off-by: Amos Kong <address@hidden>
>
> Let's see what Rusty says about the spec change.
Implementation notes like this belong as a footnote, eg:
For older systems, it is recommended and typical that the device
write byte 5 of the mac address last, so devices can use that as
a trigger to commit the mac address change.
Now, is this a real, or theoretical issue? Have we seen this problem in
practice, or should we continue to ignore it?
Cheers,
Rusty.
Re: [Qemu-devel] [RFC virt-spec PATCH] only writing out the last byte of MAC makes it have effect, Michael S. Tsirkin, 2013/03/21