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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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

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@xxxxxxxxxx>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


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