[PATCH 11/11] xen/hvm kdump: reset PV devices in crash kernel

[Olaf Hering <olaf@aepfle.de>]

[-- Attachment #1: xen.pv-on-hvm.kdump.patch --]
[-- Type: text/plain, Size: 4943 bytes --]

(this is actually a forward port of rev 1079 from 2.6.18.hg, untested because
kdump just hangs before (or while) entering the crash kernel in 3.0)

After triggering a crash dump in a HVM guest, the PV backend drivers
will remain in connected state. When the kdump kernel starts the PV
drivers will skip such devices. As a result, no root device is found and
the vmcore cant be saved.

With this change all frontend devices with state XenbusStateConnected
will be reset by changing the state file to Closing/Closed/Initializing.
This will trigger a disconnect in the backend drivers. Now the frontend
drivers will find the backend drivers in state Initwait and can connect.

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
 drivers/xen/xenbus/xenbus_comms.c          |    4 -
 drivers/xen/xenbus/xenbus_probe_frontend.c |   97 +++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 1 deletion(-)

Index: linux-3.0/drivers/xen/xenbus/xenbus_comms.c
===================================================================
--- linux-3.0.orig/drivers/xen/xenbus/xenbus_comms.c
+++ linux-3.0/drivers/xen/xenbus/xenbus_comms.c
@@ -212,7 +212,9 @@ int xb_init_comms(void)
 		printk(KERN_WARNING "XENBUS response ring is not quiescent "
 		       "(%08x:%08x): fixing up\n",
 		       intf->rsp_cons, intf->rsp_prod);
-		intf->rsp_cons = intf->rsp_prod;
+		/* breaks kdump */
+		if (!reset_devices)
+			intf->rsp_cons = intf->rsp_prod;
 	}
 
 	if (xenbus_irq) {
Index: linux-3.0/drivers/xen/xenbus/xenbus_probe_frontend.c
===================================================================
--- linux-3.0.orig/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ linux-3.0/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -254,10 +254,107 @@ int __xenbus_register_frontend(struct xe
 }
 EXPORT_SYMBOL_GPL(__xenbus_register_frontend);
 
+#ifdef CONFIG_CRASH_DUMP
+static DECLARE_WAIT_QUEUE_HEAD(be_state_wq);
+static int be_state;
+
+static void xenbus_reset_state_changed(struct xenbus_watch *w, const char **v, unsigned int l)
+{
+	xenbus_scanf(XBT_NIL, v[XS_WATCH_PATH], "", "%i", &be_state);
+	printk(KERN_INFO "XENBUS: %s %s\n", v[XS_WATCH_PATH], xenbus_strstate(be_state));
+	wake_up(&be_state_wq);
+}
+
+static int xenbus_reset_check_final(int *st)
+{
+	return *st == XenbusStateInitialising || *st == XenbusStateInitWait;
+}
+
+static void xenbus_reset_frontend_state(char *backend, char *frontend)
+{
+	struct xenbus_watch watch;
+
+	memset(&watch, 0, sizeof(watch));
+	watch.node = kasprintf(GFP_NOIO | __GFP_HIGH, "%s/state", backend);
+	if (!watch.node)
+		return;
+
+	watch.callback = xenbus_reset_state_changed;
+	be_state = XenbusStateUnknown;
+
+	printk(KERN_INFO "XENBUS: triggering reconnect on %s\n", backend);
+	register_xenbus_watch(&watch);
+
+	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateClosing);
+	wait_event_interruptible(be_state_wq, be_state == XenbusStateClosing);
+
+	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateClosed);
+	wait_event_interruptible(be_state_wq, be_state == XenbusStateClosed);
+
+	xenbus_printf(XBT_NIL, frontend, "state", "%d", XenbusStateInitialising);
+	wait_event_interruptible(be_state_wq, xenbus_reset_check_final(&be_state));
+
+	unregister_xenbus_watch(&watch);
+	printk(KERN_INFO "XENBUS: reconnect done on %s\n", backend);
+	kfree(watch.node);
+}
+
+static void xenbus_reset_check_state(char *class, char *dev)
+{
+	int state, err;
+	char *backend, *frontend;
+
+	frontend = kasprintf(GFP_NOIO | __GFP_HIGH, "device/%s/%s", class, dev);
+	if (!frontend)
+		return;
+
+	err = xenbus_scanf(XBT_NIL, frontend, "state", "%i", &state);
+	/* frontend connected? */
+	if (err == 1 && state == XenbusStateConnected) {
+		backend = xenbus_read(XBT_NIL, frontend, "backend", NULL);
+		if (!backend || IS_ERR(backend))
+			goto out;
+		err = xenbus_scanf(XBT_NIL, backend, "state", "%i", &state);
+		/* backend connected? */
+		if (err == 1 && state == XenbusStateConnected)
+			xenbus_reset_frontend_state(backend, frontend);
+		kfree(backend);
+	}
+out:
+	kfree(frontend);
+}
+
+static void xenbus_reset_state(void)
+{
+	char **devclass, **dev;
+	int devclass_n, dev_n;
+	int i, j;
+
+	devclass = xenbus_directory(XBT_NIL, "device", "", &devclass_n);
+	if (IS_ERR(devclass))
+		return;
+
+	for (i = 0; i < devclass_n; i++) {
+		dev = xenbus_directory(XBT_NIL, "device", devclass[i], &dev_n);
+		if (IS_ERR(dev))
+			continue;
+		for (j = 0; j < dev_n; j++)
+			xenbus_reset_check_state(devclass[i], dev[j]);
+		kfree(dev);
+	}
+	kfree(devclass);
+}
+#endif
+
 static int frontend_probe_and_watch(struct notifier_block *notifier,
 				   unsigned long event,
 				   void *data)
 {
+#ifdef CONFIG_CRASH_DUMP
+	/* reset devices in XenbusStateConnected state */
+	if (!xen_initial_domain() && reset_devices)
+		xenbus_reset_state();
+#endif
 	/* Enumerate devices in xenstore and watch for changes. */
 	xenbus_probe_devices(&xenbus_frontend);
 	register_xenbus_watch(&fe_watch);