Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect
On Mon, Mar 25, 2013 at 08:58:49AM +0200, Michael S. Tsirkin wrote:
On Mon, Mar 25, 2013 at 10:23:57AM +0800, Amos Kong wrote:
On Fri, Mar 22, 2013 at 10:45:09AM +1030, Rusty Russell wrote:
Michael S. Tsirkin m...@redhat.com 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 ak...@redhat.com
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?
Hi Rusty, Michael
I didn't touch any problem. MST, and you?
In Linux guest, we should disable the interface before changing mac address.
ifconfig eth0 down
ifconfig eth0 hw ether 10:12:13:14:15:16
ifconfig eth0 up
In Windows 7 guest, after changing mac address in register table,
re-enabling interface to make it effect.
reg add HKLM
SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\0001]
/v NetworkAddress /d 0123456789AB
netsh interface set interface Local Area Connection DISABLED
netsh interface set interface Local Area Connection ENABLED
So when we change the mac address, guest os always disable interface
to receive all packages. It seems the theoretical issue doesn't exist?
Cheers,
Rusty.
--
Amos.
Nope. Looks like no spec change is necessary. We already say it's
not atomic and it looks like guests expect exactly that
and disable link to prevent strange issues.
I just found Jiri has a commit to allow changing mac when iface
is running. It seems only the virt nics are allowned, right?
But the leagcy guests don't allow to change mac when interface is
running, so no spec change is necessary.
[upstream kernel]
commit d4fc6918f4b3cc844185f59fc518351525950449
Author: Jiri Pirko jpi...@redhat.com
Date: Wed Jun 27 05:27:46 2012 +
virtio_net: allow to change mac when iface is running
Signed-off-by: Jiri Pirko jpi...@redhat.com
Signed-off-by: David S. Miller da...@davemloft.net
RH-BZ: https://bugzilla.redhat.com/show_bug.cgi?id=882868
--
Amos.
Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect
On Mon, Mar 25, 2013 at 10:23:57AM +0800, Amos Kong wrote:
On Fri, Mar 22, 2013 at 10:45:09AM +1030, Rusty Russell wrote:
Michael S. Tsirkin m...@redhat.com 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 ak...@redhat.com
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?
Hi Rusty, Michael
I didn't touch any problem. MST, and you?
In Linux guest, we should disable the interface before changing mac address.
ifconfig eth0 down
ifconfig eth0 hw ether 10:12:13:14:15:16
ifconfig eth0 up
In Windows 7 guest, after changing mac address in register table,
re-enabling interface to make it effect.
reg add HKLM
SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\0001]
/v NetworkAddress /d 0123456789AB
netsh interface set interface Local Area Connection DISABLED
netsh interface set interface Local Area Connection ENABLED
So when we change the mac address, guest os always disable interface
to receive all packages. It seems the theoretical issue doesn't exist?
Cheers,
Rusty.
--
Amos.
Nope. Looks like no spec change is necessary. We already say it's
not atomic and it looks like guests expect exactly that
and disable link to prevent strange issues.
--
MST
Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect
On Fri, Mar 22, 2013 at 10:45:09AM +1030, Rusty Russell wrote:
Michael S. Tsirkin m...@redhat.com 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 ak...@redhat.com
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?
Hi Rusty, Michael
I didn't touch any problem. MST, and you?
In Linux guest, we should disable the interface before changing mac address.
ifconfig eth0 down
ifconfig eth0 hw ether 10:12:13:14:15:16
ifconfig eth0 up
In Windows 7 guest, after changing mac address in register table,
re-enabling interface to make it effect.
reg add HKLM
SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}\0001]
/v NetworkAddress /d 0123456789AB
netsh interface set interface Local Area Connection DISABLED
netsh interface set interface Local Area Connection ENABLED
So when we change the mac address, guest os always disable interface
to receive all packages. It seems the theoretical issue doesn't exist?
Cheers,
Rusty.
--
Amos.
Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect
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 ak...@redhat.com
Let's see what Rusty says about the spec change.
---
hw/virtio.c |3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)
diff --git a/hw/virtio.c b/hw/virtio.c
index 26fbc79..2e08302 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -605,8 +605,9 @@ void virtio_config_writeb(VirtIODevice *vdev, uint32_t
addr, uint32_t data)
stb_p(vdev-config + addr, val);
-if (vdev-set_config)
+if (vdev-set_config (addr == 5 || strcmp(vdev-name, virtio-net)))
{
vdev-set_config(vdev, vdev-config);
+}
}
void virtio_config_writew(VirtIODevice *vdev, uint32_t addr, uint32_t data)
--
1.7.1
Re: [Qemu-devel] [RFC qemu PATCH] only writing out the last byte of MAC makes it have effect
Michael S. Tsirkin m...@redhat.com 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 ak...@redhat.com 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.
