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Re: [Qemu-devel] [PATCH] virtio-net: require that config size is initial

From: KONRAD Frédéric
Subject: Re: [Qemu-devel] [PATCH] virtio-net: require that config size is initialized
Date: Tue, 07 May 2013 17:29:34 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130311 Thunderbird/17.0.4

On 07/05/2013 16:00, Michael S. Tsirkin wrote:
On Tue, May 07, 2013 at 02:54:38PM +0200, KONRAD Frédéric wrote:
On 07/05/2013 14:33, Michael S. Tsirkin wrote:
On Tue, May 07, 2013 at 02:29:38PM +0200, KONRAD Frédéric wrote:

I think it is not a good idea, as we wanted to make VirtIODevice
hot-pluggable for virtio-mmio.
And then this hack will break cross version migration.

virtio_net_set_config_size is called by each "proxy" devices no?
If it's called then there's no need for a default,
so this patch should be fine.

True but as I told you, we made this refactoring to be able to hot-plug
VirtIODevice on a virtio-bus, so calling this function won't be possible.

But you are right this must be fixed.

Maybe we can use a callback which is called by virtio-bus before
plugging, to ensure that this
config size is computed?
OK, will you post such a patch?

The issue is as we said in the last thread, host_feature is part of
the proxy.
Maybe you could add documentation on how initialization works?
If I could fiure it out I would maybe suggest some solutions.

Yes, where do you think I can add this?

And if we want to move it to the devices, we must have a kind of
property forwarding mechanism.

Anthony said he had something about that.
All buses do this, and if they don't they get subtle
bugs related to cross version migration.
Let's add an assert to catch these bugs early.

Signed-off-by: Michael S. Tsirkin <address@hidden>

Just a cleanup so not 1.5 material.
Seems to work fine here - any opinions?

  hw/net/virtio-net.c | 7 ++++---
  1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 908e7b8..f0a9272 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1282,6 +1282,8 @@ static int virtio_net_device_init(VirtIODevice *vdev)
      DeviceState *qdev = DEVICE(vdev);
      VirtIONet *n = VIRTIO_NET(vdev);
+    /* Verify that config size has been initialized */
+    assert(n->config_size != (size_t)-1);
      virtio_init(VIRTIO_DEVICE(n), "virtio-net", VIRTIO_ID_NET,
@@ -1386,10 +1388,9 @@ static void virtio_net_instance_init(Object *obj)
      VirtIONet *n = VIRTIO_NET(obj);
-     * The default config_size is sizeof(struct virtio_net_config).
-     * Can be overriden with virtio_net_set_config_size.
+     * The config_size must be set later with virtio_net_set_config_size.
-    n->config_size = sizeof(struct virtio_net_config);
+    n->config_size = (size_t)-1;
  static Property virtio_net_properties[] = {

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