On Thu, Apr 05, 2012 at 01:56:15PM +0800, Jason Wang wrote:

On 04/04/2012 03:49 PM, Michael S. Tsirkin wrote:

quoted

On Wed, Mar 28, 2012 at 01:44:28PM +0800, Jason Wang wrote:

quoted

As hypervior does not have the knowledge of guest network configuration, it's
better to ask guest to send gratuitous packets when needed.

Guest tests VIRTIO_NET_S_ANNOUNCE bit during config change interrupt and when it
is set, a workqueue is scheduled to send gratuitous packet through
NETDEV_NOTIFY_PEERS. This feature is negotiated through bit
VIRTIO_NET_F_GUEST_ANNOUNCE.

Changes from v5:
- notify the chain before acking the link annoucement
- ack the link announcement notification through control vq

Changes from v4:
- typos
- handle workqueue unconditionally
- move VIRTIO_NET_S_ANNOUNCE to bit 8 to separate rw bits from ro bits

Changes from v3:
- cancel the workqueue during freeze

Changes from v2:
- fix the race between unregister_dev() and workqueue

Signed-off-by: Jason Wang<jasowang@redhat.com>

I think this needs some fixes. See below.
Thanks.

quoted

---
 drivers/net/virtio_net.c   |   32 +++++++++++++++++++++++++++++++-
 include/linux/virtio_net.h |   13 +++++++++++++
 2 files changed, 44 insertions(+), 1 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4880aa8..0f60da7 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -72,6 +72,9 @@ struct virtnet_info {
 	/* Work struct for refilling if we run low on memory. */
 	struct delayed_work refill;

+	/* Work struct for sending gratuitous packets. */

A bit confusing: it does not send anything itself.
A better comment 'for announcing the existence of device
on the network'.

quoted

+	struct work_struct announce;
+
 	/* Chain pages by the private ptr. */
 	struct page *pages;

@@ -781,12 +784,30 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
 	return status == VIRTIO_NET_OK;
 }

+static void virtnet_ack_link_announce(struct virtnet_info *vi)
+{
+	if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_ANNOUNCE,
+				  VIRTIO_NET_CTRL_ANNOUNCE_ACK, NULL,
+				  0, 0)) {

This can run in parallel with other commands. That's pretty bad -
will corrupt the cvq.
Take rtnl lock around calls to this function?

It's only used by callbacks of netif_notify_peers(), so rtnl lock
have already been hold. Add a comment to clarify this?

quoted

quoted

+		dev_warn(&vi->dev->dev, "Failed to ack link nnounce.\n");

announce

Sorry for the typos, would double check in the future.

quoted

quoted

+	}

Better to drop {} around a single statement.

quoted

+}
+
+static void announce_work(struct work_struct *work)
+{
+	struct virtnet_info *vi = container_of(work, struct virtnet_info,
+					       announce);
+	netif_notify_peers(vi->dev);
+	virtnet_ack_link_announce(vi);
+}
+
 static int virtnet_close(struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);

 	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
+	cancel_work_sync(&vi->announce);

I think that a config change event can trigger after this point,
so cancel here won't be effective. But why do it here?
virtnet_remove not a better place? We can do it
after remove_vq_common.

Sure.

Except, trying to send a command on cvq after device
has been reset would deadlock. I suspect we'll need
a flag like block has to prevent this.

quoted

quoted

 	napi_disable(&vi->napi);

 	return 0;

@@ -962,11 +983,17 @@ static void virtnet_update_status(struct virtnet_info *vi)
 		return;

 	/* Ignore unknown (future) status bits */
-	v&= VIRTIO_NET_S_LINK_UP;
+	v&= VIRTIO_NET_S_LINK_UP | VIRTIO_NET_S_ANNOUNCE;

The announce bit in vi->status is always clear,
so this is IMO confusing. I would do:

if (v&  VIRTIO_NET_S_ANNOUNCE) {
	schedule
}

v&= VIRTIO_NET_S_LINK_UP;

and the rest of the logic is not necessary then.

Also, this might run extra ack announce commands after
VIRTIO_NET_S_ANNOUNCE bit is clear. The spec
isn't clear on whether this is legal.

It would be very hard to fix this, so let's add a comment
stating that it's legal, and clarify the spec
in any case.

How about delay the clearing of VIRTIO_NET_S_ANNOUNCE bit in the
workqueue and protect the updating with
spinlock_irqsave()/spinloc_irqrestore()? Then later notification
would be suppressed if the sending is not completed.

Not sure what's meant, just make sure we don't lose
these events.

quoted

quoted

 	if (vi->status == v)
 		return;

+	if (v&  VIRTIO_NET_S_ANNOUNCE) {
+		v&= ~VIRTIO_NET_S_ANNOUNCE;
+		if (v&  VIRTIO_NET_S_LINK_UP)
+			schedule_work(&vi->announce);

I think we really want an nrt wq here - if this triggers
multiple times there's no good reason to try and run
the ack command many times in parallel.

Yes.

quoted

quoted

+	}
+
 	vi->status = v;

 	if (vi->status&  VIRTIO_NET_S_LINK_UP) {

quoted

@@ -1076,6 +1103,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 		goto free;

 	INIT_DELAYED_WORK(&vi->refill, refill_work);
+	INIT_WORK(&vi->announce, announce_work);
 	sg_init_table(vi->rx_sg, ARRAY_SIZE(vi->rx_sg));
 	sg_init_table(vi->tx_sg, ARRAY_SIZE(vi->tx_sg));

@@ -1187,6 +1215,7 @@ static int virtnet_freeze(struct virtio_device *vdev)
 	virtqueue_disable_cb(vi->svq);
 	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ))
 		virtqueue_disable_cb(vi->cvq);
+	cancel_work_sync(&vi->announce);

A config change event can trigger after this point,
so cancel here won't be effective.
Possibly, we need state like config_enable in the block
device.

Probably needed.

quoted

Also, what exactly will happen on suspend?
As we reset, ANNOUCE bit will be clear so -
do we forget to announce? Probably not good ...

This problem should be the same as normal suspending/resuming, if
user want to announce the link they should use arp_notify instead.

quoted

quoted

 	netif_device_detach(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);

@@ -1233,6 +1262,7 @@ static unsigned int features[] = {
 	VIRTIO_NET_F_GUEST_ECN, VIRTIO_NET_F_GUEST_UFO,
 	VIRTIO_NET_F_MRG_RXBUF, VIRTIO_NET_F_STATUS, VIRTIO_NET_F_CTRL_VQ,
 	VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN,
+	VIRTIO_NET_F_GUEST_ANNOUNCE,
 };

 static struct virtio_driver virtio_net_driver = {

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 970d5a2..383e8a0 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h

@@ -49,8 +49,10 @@
 #define VIRTIO_NET_F_CTRL_RX	18	/* Control channel RX mode support */
 #define VIRTIO_NET_F_CTRL_VLAN	19	/* Control channel VLAN filtering */
 #define VIRTIO_NET_F_CTRL_RX_EXTRA 20	/* Extra RX mode control support */
+#define VIRTIO_NET_F_GUEST_ANNOUNCE 21  /* Guest can send gratituous packet */

Rusty aligned the comments using tabs so let's do it here too?
A better comment 'can announce device on the network'.

quoted

 #define VIRTIO_NET_S_LINK_UP	1	/* Link is up */
+#define VIRTIO_NET_S_ANNOUNCE   2	/* Announcement is needed */

why 3 spaces before the value here?

quoted

 struct virtio_net_config {
 	/* The config defining mac address (if VIRTIO_NET_F_MAC) */

@@ -152,4 +154,15 @@ struct virtio_net_ctrl_mac {
  #define VIRTIO_NET_CTRL_VLAN_ADD             0
  #define VIRTIO_NET_CTRL_VLAN_DEL             1

+/*
+ * Control link announce acknowledgement
+ *
+ * The command VIRTIO_NET_CTRL_ANNOUNCE_ACK is used to indicate that
+ * driver has recevied the notification and device would clear the

s/recevied/received/

A bit clearer to replace 'and' with ; here.

quoted

+ * VIRTIO_NET_S_ANNOUNCE bit in the status filed after it received

s/filed/field/
s/received/receives/

quoted

+ * this command.
+ */
+#define VIRTIO_NET_CTRL_ANNOUNCE       3
+ #define VIRTIO_NET_CTRL_ANNOUNCE_ACK         0
+
 #endif /* _LINUX_VIRTIO_NET_H */

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