[PATCH V2 1/3] virtio: allow nested disabling of the configure interrupt

[Jason Wang <jasowang@xxxxxxxxxx>]

Somtime driver may want to enable or disable the config callback. This
requires a synchronization with the core. So this patch change the
config_enabled to be a integer counter. This allows the toggling of
the config_enable to be synchronized between the virtio core and the
virtio driver.

The counter is not allowed to be increased greater than one, this
simplifies the logic where the interrupt could be disabled immediately
without extra synchronization between driver and core.

Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/virtio/virtio.c | 20 +++++++++++++-------
 include/linux/virtio.h  |  2 +-
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index b968b2aa5f4d..d3aa74b8ae5d 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -127,7 +127,7 @@ static void __virtio_config_changed(struct virtio_device *dev)
 {
 	struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
 
-	if (!dev->config_enabled)
+	if (dev->config_enabled < 1)
 		dev->config_change_pending = true;
 	else if (drv && drv->config_changed)
 		drv->config_changed(dev);
@@ -146,17 +146,23 @@ EXPORT_SYMBOL_GPL(virtio_config_changed);
 static void virtio_config_disable(struct virtio_device *dev)
 {
 	spin_lock_irq(&dev->config_lock);
-	dev->config_enabled = false;
+	--dev->config_enabled;
 	spin_unlock_irq(&dev->config_lock);
 }
 
 static void virtio_config_enable(struct virtio_device *dev)
 {
 	spin_lock_irq(&dev->config_lock);
-	dev->config_enabled = true;
-	if (dev->config_change_pending)
-		__virtio_config_changed(dev);
-	dev->config_change_pending = false;
+
+	if (dev->config_enabled < 1) {
+		++dev->config_enabled;
+		if (dev->config_enabled == 1 &&
+		    dev->config_change_pending) {
+			__virtio_config_changed(dev);
+			dev->config_change_pending = false;
+		}
+	}
+
 	spin_unlock_irq(&dev->config_lock);
 }
 
@@ -455,7 +461,7 @@ int register_virtio_device(struct virtio_device *dev)
 		goto out_ida_remove;
 
 	spin_lock_init(&dev->config_lock);
-	dev->config_enabled = false;
+	dev->config_enabled = 0;
 	dev->config_change_pending = false;
 
 	INIT_LIST_HEAD(&dev->vqs);
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 96fea920873b..4496f9ba5d82 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -132,7 +132,7 @@ struct virtio_admin_cmd {
 struct virtio_device {
 	int index;
 	bool failed;
-	bool config_enabled;
+	int config_enabled;
 	bool config_change_pending;
 	spinlock_t config_lock;
 	spinlock_t vqs_list_lock;
-- 
2.31.1