linux-kernel - Re: [PATCH] virtio: remove virtio-pci root device

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Date:	Mon, 10 Jan 2011 13:22:05 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Milton Miller <miltonm@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Anthony Liguori <aliguori@...ibm.com>,
	Jamie Lokier <jamie@...reable.org>,
	Thomas Weber <swirl@....li>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio: remove virtio-pci root device

On Mon, Jan 10, 2011 at 01:18:59PM +0200, Gleb Natapov wrote:
> On Sun, Jan 09, 2011 at 05:18:21PM +0200, Michael S. Tsirkin wrote:
> > On Fri, Jan 07, 2011 at 02:55:06AM -0600, Milton Miller 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.
> > > 
> > > Instead of creating a top-level devices/virtio-pci
> > > directory, create each device under the corresponding
> > > pci device node.  Symlinks to all virtio-pci
> > > devices can be found under the pci driver link in
> > > bus/pci/drivers/virtio-pci/devices, and all virtio
> > > devices under drivers/bus/virtio/devices.
> > > 
> > > Signed-off-by: Milton Miller <miltonm@....com>
> > 
> > OK, this works fine for me.  I played with options to add compat
> > softlinks under devices/virtio-pci but we still don't get exactly the
> > same layout and since I don't think anyone actually uses them, it's
> > probably ok to just to the simple thing.
> > 
> > Tested/Acked-by: Michael S. Tsirkin <mst@...hat.com>
> > 
> > Rusty, since this help fix at least one user, any chance this can be put
> > in 2.6.38? OK to backport to -stable?
> > 
> > Gleb, could you try this out too?
> > 
> With this patch if I have 3 virtio disks for a VM I get:
> /sys/devices/pci0000:00/0000:00:04.0/virtio0/block/vda
> /sys/devices/pci0000:00/0000:00:05.0/virtio1/block/vdb
> /sys/devices/pci0000:00/0000:00:06.0/virtio2/block/vdc
> 
> Number after virtio has no much sense. It either should be dropped at all
> or be always zero in case we will support more then one virtio controller
> per pci card. In that case each virtio controller will have directories
> virtio0/virtio1/virtio2... under same pci device directory.

Yes. But this is the bus name.  It must be unique - all devices
also appear under /sys/bus/virtio/devices.

> > > ---
> > > 
> > > This is an alternative to the patch by Michael S. Tsirkin
> > > titled "virtio-pci: add softlinks between virtio and pci"
> > > https://patchwork.kernel.org/patch/454581/
> > > 
> > > It creates simpler code, uses less memory, and should
> > > be even easier use by the installer as it won't have to
> > > know a virtio symlink to follow (just follow none).
> > > 
> > > Compile tested only as I don't have kvm setup.
> > > 
> > > 
> > > diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> > > index ef8d9d5..4fb5b2b 100644
> > > --- a/drivers/virtio/virtio_pci.c
> > > +++ b/drivers/virtio/virtio_pci.c
> > > @@ -96,11 +96,6 @@ static struct pci_device_id virtio_pci_id_table[] = {
> > >  
> > >  MODULE_DEVICE_TABLE(pci, virtio_pci_id_table);
> > >  
> > > -/* A PCI device has it's own struct device and so does a virtio device so
> > > - * we create a place for the virtio devices to show up in sysfs.  I think it
> > > - * would make more sense for virtio to not insist on having it's own device. */
> > > -static struct device *virtio_pci_root;
> > > -
> > >  /* Convert a generic virtio device to our structure */
> > >  static struct virtio_pci_device *to_vp_device(struct virtio_device *vdev)
> > >  {
> > > @@ -629,7 +624,7 @@ static int __devinit virtio_pci_probe(struct pci_dev *pci_dev,
> > >  	if (vp_dev == NULL)
> > >  		return -ENOMEM;
> > >  
> > > -	vp_dev->vdev.dev.parent = virtio_pci_root;
> > > +	vp_dev->vdev.dev.parent = &pci_dev->dev;
> > >  	vp_dev->vdev.dev.release = virtio_pci_release_dev;
> > >  	vp_dev->vdev.config = &virtio_pci_config_ops;
> > >  	vp_dev->pci_dev = pci_dev;
> > > @@ -717,17 +712,7 @@ static struct pci_driver virtio_pci_driver = {
> > >  
> > >  static int __init virtio_pci_init(void)
> > >  {
> > > -	int err;
> > > -
> > > -	virtio_pci_root = root_device_register("virtio-pci");
> > > -	if (IS_ERR(virtio_pci_root))
> > > -		return PTR_ERR(virtio_pci_root);
> > > -
> > > -	err = pci_register_driver(&virtio_pci_driver);
> > > -	if (err)
> > > -		root_device_unregister(virtio_pci_root);
> > > -
> > > -	return err;
> > > +	return pci_register_driver(&virtio_pci_driver);
> > >  }
> > >  
> > >  module_init(virtio_pci_init);
> > > @@ -735,7 +720,6 @@ module_init(virtio_pci_init);
> > >  static void __exit virtio_pci_exit(void)
> > >  {
> > >  	pci_unregister_driver(&virtio_pci_driver);
> > > -	root_device_unregister(virtio_pci_root);
> > >  }
> > >  
> > >  module_exit(virtio_pci_exit);
> 
> --
> 			Gleb.
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