linux-kernel - Re: [PATCH v3 3/3] xen/pciback: support driver

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Message-ID: <0a5ec2ee-4713-b839-6742-ab6e663db7b9@suse.com>
Date:   Fri, 23 Sep 2016 06:06:30 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     david.vrabel@...rix.com
Subject: Re: [PATCH v3 3/3] xen/pciback: support driver_override

On 22/09/16 23:10, Boris Ostrovsky wrote:
> On 09/22/2016 04:45 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.
>>
>> Up to now for assigning a pci device to pciback 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.
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>> V3: Move override check up in order not to miss the PCI_HEADER_TYPE
>>     check.
>>     Add an assigned device to the slot list.
>>
>> V2: Removed now unused label
>> ---
>>  drivers/xen/xen-pciback/pci_stub.c | 36 +++++++++++++++++++++++++++++-------
>>  1 file changed, 29 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
>> index 0179333..6331a95 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,
>> @@ -508,15 +510,18 @@ static void pcistub_device_id_add_list(struct pcistub_device_id *new,
>>  		kfree(new);
>>  }
>>  
>> -static int pcistub_seize(struct pci_dev *dev)
>> +static int pcistub_seize(struct pci_dev *dev,
>> +			 struct pcistub_device_id *pci_dev_id)
>>  {
>>  	struct pcistub_device *psdev;
>>  	unsigned long flags;
>>  	int err = 0;
>>  
>>  	psdev = pcistub_device_alloc(dev);
>> -	if (!psdev)
>> +	if (!psdev) {
>> +		kfree(pci_dev_id);
> 
> Here too --- I'd rather have it freed by whoever allocated it (i.e. the
> caller). In fact I think you can allocate this here and instead of
> passing pci_dev_id pointer pass a flag of some sort.

Allocating it here will become nasty: The allocation flags are
different in the two cases, so I'd have to either pass the flags
or have to use GFP_ATOMIC in both cases.

And dealing with an allocation failure at the very end of
pcistub_seize() would require quite some rollback action.


Juergen

> -boris
> 
>>  		return -ENOMEM;
>> +	}
>>  
>>  	spin_lock_irqsave(&pcistub_devices_lock, flags);
>>  
>> @@ -537,8 +542,12 @@ static int pcistub_seize(struct pci_dev *dev)
>>  
>>  	spin_unlock_irqrestore(&pcistub_devices_lock, flags);
>>  
>> -	if (err)
>> +	if (err) {
>> +		kfree(pci_dev_id);
>>  		pcistub_device_put(psdev);
>> +	} else if (pci_dev_id)
>> +		pcistub_device_id_add_list(pci_dev_id, pci_domain_nr(dev->bus),
>> +					   dev->bus->number, dev->devfn);
>>  
>>  	return err;
>>  }
>> @@ -547,11 +556,16 @@ static int pcistub_seize(struct pci_dev *dev)
>>   * other functions that take the sysfs lock. */
>>  static int pcistub_probe(struct pci_dev *dev, const struct pci_device_id *id)
>>  {
>> -	int err = 0;
>> +	int err = 0, match;
>> +	struct pcistub_device_id *pci_dev_id = NULL;
>>  
>>  	dev_dbg(&dev->dev, "probing...\n");
>>  
>> -	if (pcistub_match(dev)) {
>> +	match = pcistub_match(dev);
>> +
>> +	if ((dev->driver_override &&
>> +	     !strcmp(dev->driver_override, PCISTUB_DRIVER_NAME)) ||
>> +	    match) {
>>  
>>  		if (dev->hdr_type != PCI_HEADER_TYPE_NORMAL
>>  		    && dev->hdr_type != PCI_HEADER_TYPE_BRIDGE) {
>> @@ -562,8 +576,16 @@ static int pcistub_probe(struct pci_dev *dev, const struct pci_device_id *id)
>>  			goto out;
>>  		}
>>  
>> +		if (!match) {
>> +			pci_dev_id = kmalloc(sizeof(*pci_dev_id), GFP_ATOMIC);
>> +			if (!pci_dev_id) {
>> +				err = -ENOMEM;
>> +				goto out;
>> +			}
>> +		}
>> +
>>  		dev_info(&dev->dev, "seizing device\n");
>> -		err = pcistub_seize(dev);
>> +		err = pcistub_seize(dev, pci_dev_id);
>>  	} else
>>  		/* Didn't find the device */
>>  		err = -ENODEV;
>> @@ -975,7 +997,7 @@ static const struct pci_error_handlers xen_pcibk_error_handler = {
>>  static struct pci_driver xen_pcibk_pci_driver = {
>>  	/* The name should be xen_pciback, but until the tools are updated
>>  	 * we will keep it as pciback. */
>> -	.name = "pciback",
>> +	.name = PCISTUB_DRIVER_NAME,
>>  	.id_table = pcistub_ids,
>>  	.probe = pcistub_probe,
>>  	.remove = pcistub_remove,
> 
> 
>