Re: [Xen-devel] [PATCH] xen/pci: make bus notifier handler return sane values

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Wed, Aug 17, 2011 at 04:18:35PM +0100, Jan Beulich wrote:
> >>> On 17.08.11 at 16:57, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> 
> >>> wrote:
> > On Wed, Aug 17, 2011 at 09:32:32AM +0100, Jan Beulich wrote:
> >> Notifier functions are expected to return NOTIFY_* codes, not -E...
> >> ones. In particular, since the respective hypercalls failing is not
> >> fatal to the operation of the Dom0 kernel, it must be avoided to
> > 
> > So if we fail adding a PCI device, won't we be unable to actually
> > setup its MSI?
> 
> Sure (and you also can't pass through such a device), but that's no
> reason to fail the notification chain. For one, you don't know whether
> the driver is actually going to use MSI. And even if you knew, it would
> be bad behavior imo. Plus even if you want to fail the notifier chain,
> just returning a -E... value here is wrong; notifier_from_errno() ought
> to be used then.

Oh, I am not disputing that. I am just wondering whether we should add
some extra printk's if we fail, and still reutrn either NOTIFY_OK
oir NOTIFY_DONE.

That way at least in the field we will have a good inkling of what
went wrong.
> 
> Jan
> 
> >> return negative values here as those would make it appear as if
> >> NOTIFY_STOP_MASK wa set, suppressing further notification calls to
> >> other interested parties (which is also why we don't want to use
> >> notifier_from_errno() here).
> >> 
> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> >> 
> >> ---
> >>  drivers/xen/pci.c |   11 +++++------
> >>  1 file changed, 5 insertions(+), 6 deletions(-)
> >> 
> >> --- 3.1-rc2/drivers/xen/pci.c
> >> +++ 3.1-rc2-xen-pci-bus-notifier/drivers/xen/pci.c
> >> @@ -86,23 +86,22 @@ static int xen_pci_notifier(struct notif
> >>                        unsigned long action, void *data)
> >>  {
> >>    struct device *dev = data;
> >> -  int r = 0;
> >>  
> >>    switch (action) {
> >>    case BUS_NOTIFY_ADD_DEVICE:
> >> -          r = xen_add_device(dev);
> >> +          xen_add_device(dev);
> >>            break;
> >>    case BUS_NOTIFY_DEL_DEVICE:
> >> -          r = xen_remove_device(dev);
> >> +          xen_remove_device(dev);
> >>            break;
> >>    default:
> >> -          break;
> >> +          return NOTIFY_DONE;
> >>    }
> >>  
> >> -  return r;
> >> +  return NOTIFY_OK;
> >>  }
> >>  
> >> -struct notifier_block device_nb = {
> >> +static struct notifier_block device_nb = {
> >>    .notifier_call = xen_pci_notifier,
> >>  };
> >>  
> >> 
> >> 
> >> 
> > 
> >> Notifier functions are expected to return NOTIFY_* codes, not -E...
> >> ones. In particular, since the respective hypercalls failing is not
> >> fatal to the operation of the Dom0 kernel, it must be avoided to
> >> return negative values here as those would make it appear as if
> >> NOTIFY_STOP_MASK wa set, suppressing further notification calls to
> >> other interested parties (which is also why we don't want to use
> >> notifier_from_errno() here).
> >> 
> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> >> 
> >> ---
> >>  drivers/xen/pci.c |   11 +++++------
> >>  1 file changed, 5 insertions(+), 6 deletions(-)
> >> 
> >> --- 3.1-rc2/drivers/xen/pci.c
> >> +++ 3.1-rc2-xen-pci-bus-notifier/drivers/xen/pci.c
> >> @@ -86,23 +86,22 @@ static int xen_pci_notifier(struct notif
> >>                        unsigned long action, void *data)
> >>  {
> >>    struct device *dev = data;
> >> -  int r = 0;
> >>  
> >>    switch (action) {
> >>    case BUS_NOTIFY_ADD_DEVICE:
> >> -          r = xen_add_device(dev);
> >> +          xen_add_device(dev);
> >>            break;
> >>    case BUS_NOTIFY_DEL_DEVICE:
> >> -          r = xen_remove_device(dev);
> >> +          xen_remove_device(dev);
> >>            break;
> >>    default:
> >> -          break;
> >> +          return NOTIFY_DONE;
> >>    }
> >>  
> >> -  return r;
> >> +  return NOTIFY_OK;
> >>  }
> >>  
> >> -struct notifier_block device_nb = {
> >> +static struct notifier_block device_nb = {
> >>    .notifier_call = xen_pci_notifier,
> >>  };
> >>  
> > 
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx 
> >> http://lists.xensource.com/xen-devel 
> 
> 

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