Re: [Xen-devel] [PATCH v2] xen/pciback: support driver_override

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 09/09/2016 02:14 AM, Juergen Gross wrote:
> 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.

I am not arguing against override mechanism.

My point is that people/tools may rely on the fact devices are always
listed in slots file. For example, libxl_pci.c parses at this file (I
haven't look at this code in details so perhaps it's only when checking
for devices assigned at boot time).


>
>> Also, do you think checking override might better be done first, before
>> testing for ID match?
> Why? I don't think this really matters.

It may provide (probably very slight) performance improvement when you
have lots of assigned devices.

-boris



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