Re: [PATCH v2] xen/pciback: support driver_override

[Juergen Gross]

On 08/09/16 16:10, Boris Ostrovsky wrote:
> On 09/02/2016 08:30 AM, Juergen Gross wrote:
>> Support the driver_override scheme introduced with commit 782a985d7af2
>> ("PCI: Introduce new device binding path using pci_dev.driver_override")
>>
>> As pcistub_probe() is called for all devices (it has to check for a
>> match based on the slot address rather than device type) it has to
>> check for driver_override set to "pciback" itself.
>>
>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>> ---
>> V2: removed now unused label
>> ---
>>  drivers/xen/xen-pciback/pci_stub.c | 16 ++++++++++------
>>  1 file changed, 10 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
>> index 258b7c3..85c28f7 100644
>> --- a/drivers/xen/xen-pciback/pci_stub.c
>> +++ b/drivers/xen/xen-pciback/pci_stub.c
>> @@ -25,6 +25,8 @@
>>  #include "conf_space.h"
>>  #include "conf_space_quirks.h"
>>  
>> +#define PCISTUB_DRIVER_NAME "pciback"
>> +
>>  static char *pci_devs_to_hide;
>>  wait_queue_head_t xen_pcibk_aer_wait_queue;
>>  /*Add sem for sync AER handling and xen_pcibk remove/reconfigue ops,
>> @@ -529,16 +531,18 @@ static int pcistub_probe(struct pci_dev *dev, const struct pci_device_id *id)
>>  				"don't have a normal (0) or bridge (1) "
>>  				"header type!\n");
>>  			err = -ENODEV;
>> -			goto out;
>>  		}
>>  
>> +	} else if (!dev->driver_override ||
>> +		   strcmp(dev->driver_override, PCISTUB_DRIVER_NAME))
>> +		/* Didn't find the device */
>> +		err = -ENODEV;
>> +
>> +	if (!err) {
>>  		dev_info(&dev->dev, "seizing device\n");
>>  		err = pcistub_seize(dev);
>> -	} else
>> -		/* Didn't find the device */
>> -		err = -ENODEV;
>> +	}
> 
> Should devices with pciback override be displayed in
> /sys/bus/pci/drivers/pciback/slots? If they should then they need to be
> either added to pcistub_device_ids or kept on some other list.

No, I don't think so. The patch is just needed to _avoid_ having to use
the slots stuff: without the patch you need something like:

echo 0000:07:10.0 > /sys/bus/pci/devices/0000\:07\:10.0/driver/unbind
echo 0000:07:10.0 > /sys/bus/pci/drivers/pciback/new_slot
echo 0000:07:10.0 > /sys/bus/pci/drivers_probe

while with the patch you can use the same mechanism as for similar
drivers like pci-stub and vfio-pci:

echo pciback > /sys/bus/pci/devices/0000\:07\:10.0/driver_override
echo 0000:07:10.0 > /sys/bus/pci/devices/0000\:07\:10.0/driver/unbind
echo 0000:07:10.0 > /sys/bus/pci/drivers_probe

So e.g. libvirt doesn't need special handling for pciback. The slot list
is necessary for assigning devices to pciback on boot, but I think the
override mechanism is better for runtime assignment.

> Also, do you think checking override might better be done first, before
> testing for ID match?

Why? I don't think this really matters.


Juergen