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

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

[Konrad Rzeszutek Wilk]

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

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

[Konrad Rzeszutek Wilk]

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

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

[Stefano Stabellini]

On Wed, 18 Apr 2012, Konrad Rzeszutek Wilk wrote:
> From: konrad <konrad@localhost.localdomain>

wrong email address


> 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.

I would rather write: "as broken toolstacks don't always initialize the
backends correctly."


> 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) {

I would name the parameter ignore_nonessential, just to make it clearer
that is not just about 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 */);
> +}

the comment is wrong


> +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
> 

Other than the comments I wrote above, I think the patch is good

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

[Konrad Rzeszutek Wilk]

On Thu, Apr 19, 2012 at 12:37:42PM +0100, Stefano Stabellini wrote:
> On Wed, 18 Apr 2012, Konrad Rzeszutek Wilk wrote:
> > From: konrad <konrad@localhost.localdomain>
> 
> wrong email address

Yeah :-)
> 
> 
> > 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.
> 
> I would rather write: "as broken toolstacks don't always initialize the
> backends correctly."

OK.
> 
> 
> > 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) {
> 
> I would name the parameter ignore_nonessential, just to make it clearer
> that is not just about vkbd

OK.
> 
> 
> > +		/* 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 */);
> > +}
> 
> the comment is wrong

Oh, PVKBD + PVFB. Right.

> 
> 
> > +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
> > 
> 
> Other than the comments I wrote above, I think the patch is good

Sweet. thx!

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

[Ian Campbell]

On Thu, 2012-03-22 at 10:44 +0000, Stefano Stabellini wrote:
> On Thu, 22 Mar 2012, Konrad Rzeszutek Wilk wrote:
> > 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"
> 
> While I do understand the issue you are trying to solve, it actually
> makes sense to have PV KBD (and PV VFB maybe in the future) in a PVonHVM
> guest. In particular PV KVB is already enabled in upstream QEMU for
> PVonHVM guests because it allows users to have a keyboard and mouse
> without USB emulation, that requires lots of wakes up in QEMU.
> 
> Maybe we could just reduce the timeout in general for all the PV
> devices? After all, why are we waiting 6 minutes? I could understand 6
> seconds, but 6 minutes seem really too much.

This was increased based on empirical evidence, way back (circa
150:09c88868e344 in linux-2.6.18-xen.hg)

It really can happen when starting lots of guests on a heavily loaded
dom0 that you timeout when connecting devices, at which point the guest
fails to boot if it happened to contain the root filesystem.

Maybe a halfway house would be to wait a the longer time for more
critical devices (like disks and nics)?

Ian.

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

[Stefano Stabellini]

On Thu, 22 Mar 2012, Konrad Rzeszutek Wilk wrote:
> 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"

While I do understand the issue you are trying to solve, it actually
makes sense to have PV KBD (and PV VFB maybe in the future) in a PVonHVM
guest. In particular PV KVB is already enabled in upstream QEMU for
PVonHVM guests because it allows users to have a keyboard and mouse
without USB emulation, that requires lots of wakes up in QEMU.

Maybe we could just reduce the timeout in general for all the PV
devices? After all, why are we waiting 6 minutes? I could understand 6
seconds, but 6 minutes seem really too much.

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

[Konrad Rzeszutek Wilk]

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"

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 drivers/xen/xenbus/xenbus_probe_frontend.c |   30 ++++++++++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
index f20c5f1..80325cf 100644
--- a/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -134,7 +134,31 @@ static int read_backend_details(struct xenbus_device *xendev)
 {
 	return xenbus_read_otherend_details(xendev, "backend-id", "backend");
 }
+static bool skip_if_quirk(struct device *dev, void *data)
+{
+	struct xenbus_device *xendev = to_xenbus_device(dev);
+	struct device_driver *drv = data;
+
+	/* Is this operation limited to a particular driver? */
+	if (drv && (dev->driver != drv))
+		return false;
+
+	if (xen_pv_domain())
+		return false;
+
+	/* With older QEMU, for PVonHVM guests the guest config files could
+	 * contain: vfb = [ 'vnc=1, vnclisten=0.0.0.0 ,vncunused=1']
+	 * which is nonsensical as there is no PV FB (or PV KBD) when
+	 * running as HVM guest. */
 
+	if ((strncmp(xendev->nodename, "device/vkbd", 11) == 0))
+		return true;
+
+	if ((strncmp(xendev->nodename, "device/vfb", 10) == 0))
+		return true;
+
+	return false;
+}
 static int is_device_connecting(struct device *dev, void *data)
 {
 	struct xenbus_device *xendev = to_xenbus_device(dev);
@@ -153,6 +177,12 @@ static int is_device_connecting(struct device *dev, void *data)
 		return 0;
 
 	xendrv = to_xenbus_driver(dev->driver);
+
+	if (skip_if_quirk(dev, data)) {
+		printk(KERN_INFO "XENBUS: (quirk) Skipping : %s\n",
+		       xendev->nodename);
+		return 0;
+	}
 	return (xendev->state < XenbusStateConnected ||
 		(xendev->state == XenbusStateConnected &&
 		 xendrv->is_ready && !xendrv->is_ready(xendev)));
-- 
1.7.7.5