linux-kernel - Re: [PATCH v9 06/19] vfio/platform: return info for bound device

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Message-ID: <1415810168.16601.353.camel@ul30vt.home>
Date:	Wed, 12 Nov 2014 09:36:08 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Eric Auger <eric.auger@...aro.org>
Cc:	Antonios Motakis <a.motakis@...tualopensystems.com>,
	kvmarm@...ts.cs.columbia.edu, iommu@...ts.linux-foundation.org,
	will.deacon@....com, tech@...tualopensystems.com,
	christoffer.dall@...aro.org, kim.phillips@...escale.com,
	marc.zyngier@....com, VFIO DRIVER <kvm@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 06/19] vfio/platform: return info for bound device

On Wed, 2014-11-12 at 11:32 +0100, Eric Auger wrote:
> On 10/27/2014 07:07 PM, Antonios Motakis wrote:
> > A VFIO userspace driver will start by opening the VFIO device
> > that corresponds to an IOMMU group, and will use the ioctl interface
> > to get the basic device info, such as number of memory regions and
> > interrupts, and their properties. This patch enables the
> > VFIO_DEVICE_GET_INFO ioctl call.
> > 
> > Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
> > ---
> >  drivers/vfio/platform/vfio_platform_common.c | 23 ++++++++++++++++++++---
> >  1 file changed, 20 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/vfio/platform/vfio_platform_common.c b/drivers/vfio/platform/vfio_platform_common.c
> > index e0fdbc8..cb20526 100644
> > --- a/drivers/vfio/platform/vfio_platform_common.c
> > +++ b/drivers/vfio/platform/vfio_platform_common.c
> > @@ -43,10 +43,27 @@ static int vfio_platform_open(void *device_data)
> >  static long vfio_platform_ioctl(void *device_data,
> >  			   unsigned int cmd, unsigned long arg)
> >  {
> > -	if (cmd == VFIO_DEVICE_GET_INFO)
> > -		return -EINVAL;
> > +	struct vfio_platform_device *vdev = device_data;
> > +	unsigned long minsz;
> > +
> > +	if (cmd == VFIO_DEVICE_GET_INFO) {
> > +		struct vfio_device_info info;
> > +
> > +		minsz = offsetofend(struct vfio_device_info, num_irqs);
> > +
> > +		if (copy_from_user(&info, (void __user *)arg, minsz))
> > +			return -EFAULT;
> > +
> > +		if (info.argsz < minsz)
> > +			return -EINVAL;
> > +
> > +		info.flags = vdev->flags;
> > +		info.num_regions = 0;
> > +		info.num_irqs = 0;
> Seems a bit weird to me to enable the modality but returning zeroed
> values. Shouldn't we put that patch after VFIO_DEVICE_GET_REGION_INFO
> and VFIO_DEVICE_GET_IRQ_INFO ones?

I actually like how Antonios has started from a base framework, exposing
a device but none of the resources and then incrementally adds each
component.  It's also a good showcase of the VFIO ABI that we can do
things like this.  Thanks,

Alex

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