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

[Amos Kong]

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
-- 
1.8.1.4