linux-kernel - Re: [PATCH] vfio-mdev: fix non-standard ioctl return val causing i386 build fail

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Date:   Wed, 4 Jan 2017 08:44:02 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Kirti Wankhede <kwankhede@...dia.com>
Cc:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        <linux-kernel@...r.kernel.org>, Neo Jia <cjia@...dia.com>,
        <kvm@...r.kernel.org>
Subject: Re: [PATCH] vfio-mdev: fix non-standard ioctl return val causing
 i386 build fail

On Wed, 4 Jan 2017 18:06:57 +0530
Kirti Wankhede <kwankhede@...dia.com> wrote:

> Thanks Paul for catching this.
> 
> In that case we should go with 'long' since mdev_parent_ops->ioctl() is
> called from vfio_device_ops->ioctl() for which the return type is 'long'.

Agreed, we're mirroring the struct file_operations definition of ioctl,
so the return should be a long.  Thanks,

Alex

> On 1/4/2017 1:06 AM, Paul Gortmaker wrote:
> > What appears to be a copy and paste error from the line above gets
> > the ioctl a ssize_t return value instead of the traditional "int".
> > 
> > The associated sample code used "long" which meant it would compile
> > for x86-64 but not i386, with the latter failing as follows:
> > 
> >   CC [M]  samples/vfio-mdev/mtty.o
> > samples/vfio-mdev/mtty.c:1418:20: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
> >   .ioctl          = mtty_ioctl,
> >                     ^
> > samples/vfio-mdev/mtty.c:1418:20: note: (near initialization for ‘mdev_fops.ioctl’)
> > cc1: some warnings being treated as errors
> > 
> > Use the standard "int" ioctl return value in both the header and
> > the sample code to fix the issue.
> > 
> > Fixes: 9d1a546c53b4 ("docs: Sample driver to demonstrate how to use Mediated device framework.")
> > Cc: Kirti Wankhede <kwankhede@...dia.com>
> > Cc: Neo Jia <cjia@...dia.com>
> > Cc: Alex Williamson <alex.williamson@...hat.com>
> > Cc: kvm@...r.kernel.org
> > Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
> > ---
> >  include/linux/mdev.h     | 2 +-
> >  samples/vfio-mdev/mtty.c | 2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/mdev.h b/include/linux/mdev.h
> > index 3ee44b8d2bb3..46659572ab00 100644
> > --- a/include/linux/mdev.h
> > +++ b/include/linux/mdev.h
> > @@ -78,7 +78,7 @@ struct mdev_parent_ops {
> >  			size_t count, loff_t *ppos);
> >  	ssize_t (*write)(struct mdev_device *mdev, const char __user *buf,
> >  			 size_t count, loff_t *ppos);
> > -	ssize_t (*ioctl)(struct mdev_device *mdev, unsigned int cmd,
> > +	int	(*ioctl)(struct mdev_device *mdev, unsigned int cmd,
> >  			 unsigned long arg);
> >  	int	(*mmap)(struct mdev_device *mdev, struct vm_area_struct *vma);
> >  };
> > diff --git a/samples/vfio-mdev/mtty.c b/samples/vfio-mdev/mtty.c
> > index 919c10d5b12e..6f0713b1f717 100644
> > --- a/samples/vfio-mdev/mtty.c
> > +++ b/samples/vfio-mdev/mtty.c
> > @@ -1147,7 +1147,7 @@ int mtty_get_device_info(struct mdev_device *mdev,
> >  	return 0;
> >  }
> >  
> > -static long mtty_ioctl(struct mdev_device *mdev, unsigned int cmd,
> > +static int mtty_ioctl(struct mdev_device *mdev, unsigned int cmd,
> >  			unsigned long arg)
> >  {
> >  	int ret = 0;
> >