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

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Message-ID: <CAG8rG2z_iCXEDGnfuZW_g+29NjhRXzUaDG3AUEVh1zvbf298BA@mail.gmail.com>
Date:	Thu, 20 Nov 2014 15:10:50 +0100
From:	Antonios Motakis <a.motakis@...tualopensystems.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	Eric Auger <eric.auger@...aro.org>,
	kvm-arm <kvmarm@...ts.cs.columbia.edu>,
	Linux IOMMU <iommu@...ts.linux-foundation.org>,
	Will Deacon <will.deacon@....com>,
	VirtualOpenSystems Technical Team <tech@...tualopensystems.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Kim Phillips <kim.phillips@...escale.com>,
	Marc Zyngier <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, Nov 12, 2014 at 5:36 PM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> 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,

I also agree with Alex with this. But of course I'm not married with
any particular splitting style, in case we decide to change this.

>
> Alex
>
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