[PATCH] xen/xenbus: Add quirk to deal with misconfigured backends.

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

From: konrad <konrad@localhost.localdomain>

A rather annoying and common case is when booting a PVonHVM guest
and exposing the PV KBD and PV VFB - as both of those do not
make any sense. The HVM guest is using the VGA driver and the emulated
keyboard for this. So we provide a very basic quirk framework
(can be expanded in the future) to not wait for 6 minutes for those devices
to initialize - they never wont.

To trigger this, put this in your guest config:

vfb = [ 'vnc=1, vnclisten=0.0.0.0 ,vncunused=1']

instead of this:
vnc=1
vnclisten="0.0.0.0"

[v3: Split delay in non-essential (30 seconds) and essential
 devices per Ian and Stefano suggestion]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>quirk
---
 drivers/xen/xenbus/xenbus_probe_frontend.c |   69 +++++++++++++++++++++------
 1 files changed, 53 insertions(+), 16 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
index f20c5f1..7422913 100644
--- a/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -135,7 +135,7 @@ static int read_backend_details(struct xenbus_device *xendev)
 	return xenbus_read_otherend_details(xendev, "backend-id", "backend");
 }
 
-static int is_device_connecting(struct device *dev, void *data)
+static int is_device_connecting(struct device *dev, void *data, bool ignore_vkbd)
 {
 	struct xenbus_device *xendev = to_xenbus_device(dev);
 	struct device_driver *drv = data;
@@ -152,16 +152,41 @@ static int is_device_connecting(struct device *dev, void *data)
 	if (drv && (dev->driver != drv))
 		return 0;
 
+	if (ignore_vkbd) {
+		/* With older QEMU, for PVonHVM guests the guest config files
+		 * could contain: vfb = [ 'vnc=1, vnclisten=0.0.0.0']
+		 * which is nonsensical as there is no PV FB (there can be
+		 * a PVKB) running as HVM guest. */
+
+		if ((strncmp(xendev->nodename, "device/vkbd", 11) == 0))
+			return 0;
+
+		if ((strncmp(xendev->nodename, "device/vfb", 10) == 0))
+			return 0;
+	}
 	xendrv = to_xenbus_driver(dev->driver);
 	return (xendev->state < XenbusStateConnected ||
 		(xendev->state == XenbusStateConnected &&
 		 xendrv->is_ready && !xendrv->is_ready(xendev)));
 }
+static int essential_device_connecting(struct device *dev, void *data)
+{
+	return is_device_connecting(dev, data, true /* ignore PVKB+PVDB */);
+}
+static int non_essential_device_connecting(struct device *dev, void *data)
+{
+	return is_device_connecting(dev, data, false);
+}
 
-static int exists_connecting_device(struct device_driver *drv)
+static int exists_essential_connecting_device(struct device_driver *drv)
 {
 	return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
-				is_device_connecting);
+				essential_device_connecting);
+}
+static int exists_non_essential_connecting_device(struct device_driver *drv)
+{
+	return bus_for_each_dev(&xenbus_frontend.bus, NULL, drv,
+				non_essential_device_connecting);
 }
 
 static int print_device_status(struct device *dev, void *data)
@@ -192,6 +217,23 @@ static int print_device_status(struct device *dev, void *data)
 /* We only wait for device setup after most initcalls have run. */
 static int ready_to_wait_for_devices;
 
+static bool wait_loop(unsigned long start, unsigned int max_delay,
+		     unsigned int *seconds_waited)
+{
+	if (time_after(jiffies, start + (*seconds_waited+5)*HZ)) {
+		if (!*seconds_waited)
+			printk(KERN_WARNING "XENBUS: Waiting for "
+			       "devices to initialise: ");
+		*seconds_waited += 5;
+		printk("%us...", max_delay - *seconds_waited);
+		if (*seconds_waited == max_delay)
+			return true;
+	}
+
+	schedule_timeout_interruptible(HZ/10);
+
+	return false;
+}
 /*
  * On a 5-minute timeout, wait for all devices currently configured.  We need
  * to do this to guarantee that the filesystems and / or network devices
@@ -215,19 +257,14 @@ static void wait_for_devices(struct xenbus_driver *xendrv)
 	if (!ready_to_wait_for_devices || !xen_domain())
 		return;
 
-	while (exists_connecting_device(drv)) {
-		if (time_after(jiffies, start + (seconds_waited+5)*HZ)) {
-			if (!seconds_waited)
-				printk(KERN_WARNING "XENBUS: Waiting for "
-				       "devices to initialise: ");
-			seconds_waited += 5;
-			printk("%us...", 300 - seconds_waited);
-			if (seconds_waited == 300)
-				break;
-		}
-
-		schedule_timeout_interruptible(HZ/10);
-	}
+	while (exists_non_essential_connecting_device(drv))
+		if (wait_loop(start, 30, &seconds_waited))
+			break;
+
+	/* Skips PVKB and PVFB check.*/
+	while (exists_essential_connecting_device(drv))
+		if (wait_loop(start, 270, &seconds_waited))
+			break;
 
 	if (seconds_waited)
 		printk("\n");
-- 
1.7.7.5