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 18:06:57 +0530
From:   Kirti Wankhede <kwankhede@...dia.com>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>,
        <linux-kernel@...r.kernel.org>
CC:     Neo Jia <cjia@...dia.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        <kvm@...r.kernel.org>
Subject: Re: [PATCH] vfio-mdev: fix non-standard ioctl return val causing i386
 build fail


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'.

Thanks,
Kirti

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;
>