virtio: reset function
A reset function solves three problems:
1) It allows us to renegotiate features, eg. if we want to upgrade a
guest driver without rebooting the guest.
2) It gives us a clean way of shutting down virtqueues: after a reset,
we know that the buffers won't be used by the host, and
3) It helps the guest recover from messed-up drivers.
So we remove the ->shutdown hook, and the only way we now remove
feature bits is via reset.
We leave it to the driver to do the reset before it deletes queues:
the balloon driver, for example, needs to chat to the host in its
remove function.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index ced5b44..84f85e2 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -54,7 +54,7 @@
*
* The configuration information for a device consists of one or more
* virtqueues, a feature bitmaks, and some configuration bytes. The
- * configuration bytes don't really matter to us: the Launcher set them up, and
+ * configuration bytes don't really matter to us: the Launcher sets them up, and
* the driver will look at them during setup.
*
* A convenient routine to return the device's virtqueue config array:
@@ -139,9 +139,20 @@
static void lg_set_status(struct virtio_device *vdev, u8 status)
{
+ BUG_ON(!status);
to_lgdev(vdev)->desc->status = status;
}
+/* To reset the device, we (ab)use the NOTIFY hypercall, with the descriptor
+ * address of the device. The Host will zero the status and all the
+ * features. */
+static void lg_reset(struct virtio_device *vdev)
+{
+ unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;
+
+ hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0);
+}
+
/*
* Virtqueues
*
@@ -279,6 +290,7 @@
.set = lg_set,
.get_status = lg_get_status,
.set_status = lg_set_status,
+ .reset = lg_reset,
.find_vq = lg_find_vq,
.del_vq = lg_del_vq,
};