uio_hv_generic: add rescind support

When host rescinds the device, the UIO driver will clear the interrupt
state and notify application. The read (or write) on the interrupt FD
will then fail with -EIO. This is simpler than adding lots extra uevent
stuff inside UIO.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/uio-howto.rst

@@ -698,6 +698,10 @@ prevents the device from generating further interrupts until the bit is
 cleared. The userspace driver should clear this bit before blocking and
 waiting for more interrupts.
 
+When host rescinds a device, the interrupt file descriptor is marked down
+and any reads of the interrupt file descriptor will return -EIO. Similar
+to a closed socket or disconnected serial device.
+
 The vmbus device regions are mapped into uio device resources:
     0) Channel ring buffers: guest to host and host to guest
     1) Guest to host interrupt signalling pages

drivers/uio/uio_hv_generic.c

@@ -103,6 +103,23 @@ static void hv_uio_channel_cb(void *context)
 	uio_event_notify(&pdata->info);
 }
 
+/*
+ * Callback from vmbus_event when channel is rescinded.
+ */
+static void hv_uio_rescind(struct vmbus_channel *channel)
+{
+	struct hv_device *hv_dev = channel->primary_channel->device_obj;
+	struct hv_uio_private_data *pdata = hv_get_drvdata(hv_dev);
+
+	/*
+	 * Turn off the interrupt file handle
+	 * Next read for event will return -EIO
+	 */
+	pdata->info.irq = 0;
+
+	/* Wake up reader */
+	uio_event_notify(&pdata->info);
+}
 
 static void
 hv_uio_cleanup(struct hv_device *dev, struct hv_uio_private_data *pdata)
@@ -218,6 +235,8 @@ hv_uio_probe(struct hv_device *dev,
 		goto fail_close;
 	}
 
+	vmbus_set_chn_rescind_callback(dev->channel, hv_uio_rescind);
+
 	hv_set_drvdata(dev, pdata);
 
 	return 0;