linux-kernel - Re: [PATCH v5 1/4] uio: add ioctl support

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Date:	Wed, 7 Oct 2015 18:21:12 +0100
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Vlad Zolotarov <vladz@...udius-systems.com>
Cc:	linux-kernel@...r.kernel.org, mst@...hat.com, hjk@...sjkoch.de,
	corbet@....net, bruce.richardson@...el.com,
	avi@...udius-systems.com, gleb@...udius-systems.com,
	stephen@...workplumber.org, alexander.duyck@...il.com
Subject: Re: [PATCH v5 1/4] uio: add ioctl support

On Wed, Oct 07, 2015 at 11:55:01AM +0300, Vlad Zolotarov wrote:
> 
> 
> On 10/07/15 11:46, Greg KH wrote:
> >On Tue, Oct 06, 2015 at 08:17:36PM +0300, Vlad Zolotarov wrote:
> >>Add the ability for underlying device drivers to register the ioctl
> >>commands. This is useful when some interaction with the user space
> >>beyond sysfs capabilities is required, e.g. query the interrupt mode
> >>or bind eventfd to interrupt notifications (similarly to vfio ioctl
> >>VFIO_DEVICE_SET_IRQS).
> >>
> >>Signed-off-by: Vlad Zolotarov <vladz@...udius-systems.com>
> >>---
> >>  drivers/uio/uio.c          | 15 +++++++++++++++
> >>  include/linux/uio_driver.h |  3 +++
> >>  2 files changed, 18 insertions(+)
> >>
> >>diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> >>index 8196581..714b0e5 100644
> >>--- a/drivers/uio/uio.c
> >>+++ b/drivers/uio/uio.c
> >>@@ -704,6 +704,20 @@ static int uio_mmap(struct file *filep, struct vm_area_struct *vma)
> >>  	}
> >>  }
> >>+static long uio_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> >>+{
> >>+	struct uio_listener *listener = filep->private_data;
> >>+	struct uio_device *idev = listener->dev;
> >>+
> >>+	if (!idev->info)
> >>+		return -EIO;
> >>+
> >>+	if (!idev->info->ioctl)
> >>+		return -ENOTTY;
> >>+
> >>+	return idev->info->ioctl(idev->info, cmd, arg);
> >>+}
> >As Stephen said, I will not take this, sorry.  It opens up the ability
> >to add "new system calls" to a huge range of crappy drivers, it's
> >something that vendors have been trying to push for years and is
> >something that I will not allow.
> 
> Ok. Another alternative could be to add new sysfs attributes for the MSI-X
> functionality similarly to what is done with "maps".
> Would it be acceptable?

If you get everyone else here to agree that this is the interface you
all are going to be using, sure.  All I care is that you not add ioctl
to the UIO interface.

greg k-h
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