linux-kernel - Re: [PATCH] virtio-pci: add softlinks between virtio and pci

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Message-ID: <4D24CF51.3050207@codemonkey.ws>
Date:	Wed, 05 Jan 2011 14:06:41 -0600
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Jamie Lokier <jamie@...reable.org>,
	Thomas Weber <swirl@....li>, gleb@...hat.com,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio-pci: add softlinks between virtio and pci

On 01/05/2011 01:38 PM, Michael S. Tsirkin wrote:
> On Wed, Jan 05, 2011 at 01:28:34PM -0600, Anthony Liguori wrote:
>    
>> On 01/05/2011 01:17 PM, Michael S. Tsirkin wrote:
>>      
>>> We sometimes need to map between the virtio device and
>>> the given pci device. One such use is OS installer that
>>> gets the boot pci device from BIOS and needs to
>>> find the relevant block device. Since it can't,
>>> installation fails.
>>>        
>> I have no objection to this patch but I'm a tad confused by the description.
>>
>> I assume you mean the installer is querying the boot device via
>> int13 get driver parameters such that it returns the pci address of
>> the device?
>>
>> Or is it querying geometry information and then trying to find the
>> best match block device?
>>      
> I think it's the former.
>
>    
>> If it's the former, I don't really understand the need for a
>> backlink since the PCI address gives you a link to the block device.
>>      
> It does? How does it?
>    

Okay, after some more discussion, I think I better understand what's 
going on here.

The installer needs to figure out the boot device.  It does this by 
querying the BIOS and the BIOS can only give it back a PCI address.  
Right now, if you follow the PCI sysfs path, you cannot reach the actual 
virtio device because the PCI device only refers to the bus.  This is 
because virtio has a separate struct device than the PCI struct device.  
These explicit links establish the relationship.

A lot of this would be cleaner if virtio didn't force an independent 
struct device and could simply make use of an already existing struct 
device.

Regards,

Anthony Liguori

>    
>> OTOH, if it's the later, it would make sense but then your
>> description doesn't really make much sense.
>>
>> At any rate, a better commit message would be helpful in explaining
>> the need for this.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>      
>>> Supply softlinks between these to make it possible.
>>>
>>> Signed-off-by: Michael S. Tsirkin<mst@...hat.com>
>>> ---
>>>
>>> Gleb, could you please ack that this patch below
>>> will be enough to fix the installer issue that
>>> you see?
>>>
>>>   drivers/virtio/virtio_pci.c |   18 +++++++++++++++++-
>>>   1 files changed, 17 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
>>> index ef8d9d5..06eb2f8 100644
>>> --- a/drivers/virtio/virtio_pci.c
>>> +++ b/drivers/virtio/virtio_pci.c
>>> @@ -25,6 +25,7 @@
>>>   #include<linux/virtio_pci.h>
>>>   #include<linux/highmem.h>
>>>   #include<linux/spinlock.h>
>>> +#include<linux/sysfs.h>
>>>
>>>   MODULE_AUTHOR("Anthony Liguori<aliguori@...ibm.com>");
>>>   MODULE_DESCRIPTION("virtio-pci");
>>> @@ -667,8 +668,21 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
>>>   	if (err)
>>>   		goto out_set_drvdata;
>>>
>>> -	return 0;
>>> +	err = sysfs_create_link(&pci_dev->dev.kobj,&vp_dev->vdev.dev.kobj,
>>> +				"virtio_device");
>>> +	if (err)
>>> +		goto out_register_device;
>>> +
>>> +	err = sysfs_create_link(&vp_dev->vdev.dev.kobj,&pci_dev->dev.kobj,
>>> +				"bus_device");
>>> +	if (err)
>>> +		goto out_create_link;
>>>
>>> +	return 0;
>>> +out_create_link:
>>> +	sysfs_remove_link(&pci_dev->dev.kobj, "virtio_device");
>>> +out_register_device:
>>> +	unregister_virtio_device(&vp_dev->vdev);
>>>   out_set_drvdata:
>>>   	pci_set_drvdata(pci_dev, NULL);
>>>   	pci_iounmap(pci_dev, vp_dev->ioaddr);
>>> @@ -685,6 +699,8 @@ static void __devexit virtio_pci_remove(struct pci_dev *pci_dev)
>>>   {
>>>   	struct virtio_pci_device *vp_dev = pci_get_drvdata(pci_dev);
>>>
>>> +	sysfs_remove_link(&vp_dev->vdev.dev.kobj, "bus_device");
>>> +	sysfs_remove_link(&pci_dev->dev.kobj, "virtio_device");
>>>   	unregister_virtio_device(&vp_dev->vdev);
>>>   }
>>>
>>>        

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