Re: [PATCH 09/10] vfio/pci: Replace uses of vfio_device_data() with container_of

From: Christoph Hellwig <hch@lst.de>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Alex Williamson <alex.williamson@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	kvm@vger.kernel.org, "Raj, Ashok" <ashok.raj@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Daniel Vetter <daniel@ffwll.ch>,
	Leon Romanovsky <leonro@nvidia.com>,
	Max Gurtovoy <mgurtovoy@nvidia.com>,
	Tarun Gupta <targupta@nvidia.com>
Subject: Re: [PATCH 09/10] vfio/pci: Replace uses of vfio_device_data() with container_of
Date: Thu, 11 Mar 2021 12:21:24 +0100	[thread overview]
Message-ID: <20210311112124.GA17183@lst.de> (raw)
In-Reply-To: <20210310195941.GE2356281@nvidia.com>

On Wed, Mar 10, 2021 at 03:59:41PM -0400, Jason Gunthorpe wrote:
> > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> > > index af5696a96a76e0..4b0d60f7602e40 100644
> > > +++ b/drivers/vfio/pci/vfio_pci.c
> > > @@ -534,7 +534,7 @@ static struct vfio_pci_device *get_pf_vdev(struct vfio_pci_device *vdev,
> > >  		return NULL;
> > >  	}
> > >  
> > > -	return vfio_device_data(*pf_dev);
> > > +	return container_of(*pf_dev, struct vfio_pci_device, vdev);
> > 
> > I think it would be useful to just return the vfio_device and let
> > the caller do the container_of() here, maybe as a followup.
> 
> The callers seem to need the vfio_pci_device *?

Yes.  But the container_of is trivial arithmetics, no need to waste
an indirect argument for that.

> In a later series this function gets transformed into this:
> 
> 	device_lock(&physfn->dev);
> 	vdev = vfio_pci_get_drvdata(physfn);
> 	if (!vdev) {
> 		device_unlock(&physfn->dev);
> 		return NULL;
> 	}
> 	vfio_device_get(&vdev->vdev);
> 	device_unlock(&physfn->dev);
> 
> There is no container_of here because the drvdata now points at the
> struct vfio_pci_device

Ok, so discard my comment then.