linux-kernel - Re: [PATCH v3 4/8] media: subdev: remove VIDIOC_DQEVENT

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Date:   Tue, 15 Jun 2021 11:30:01 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Eduardo Valentin <edubezval@...il.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vaibhav Gupta <vaibhavgupta40@...il.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-staging@...ts.linux.dev
Subject: Re: [PATCH v3 4/8] media: subdev: remove VIDIOC_DQEVENT_TIME32 handling

On Tue, Jun 15, 2021 at 10:48 AM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>
> On 15/06/2021 10:43, Arnd Bergmann wrote:
> > On Mon, Jun 14, 2021 at 7:02 PM Laurent Pinchart
> > <laurent.pinchart@...asonboard.com> wrote:
> >>
> >> On Mon, Jun 14, 2021 at 12:34:05PM +0200, Arnd Bergmann wrote:
> >>> From: Arnd Bergmann <arnd@...db.de>
> >>>
> >>> Converting the VIDIOC_DQEVENT_TIME32/VIDIOC_DQEVENT32/
> >>> VIDIOC_DQEVENT32_TIME32 arguments to the canonical form is done in common
> >>> code, but for some reason I ended up adding another conversion helper to
> >>> subdev_do_ioctl() as well. I must have concluded that this does not go
> >>> through the common conversion, but it has done that since the ioctl
> >>> handler was first added.
> >>>
> >>> I assume this one is harmless as there should be no way to arrive here
> >>> from user space, but since it is dead code, it should just get removed.
>
> I changed this to:
>
> "I assume this one is harmless as there should be no way to arrive here
> from user space if CONFIG_COMPAT_32BIT_TIME is set,"
>
> If it is not set, then this will just fall into the default case and is
> handled as if it is a potential custom ioctl, as you would expect.
>
> Let me know if you have a better text, I can still update it.

Looks good. One more sentence I would add:

"On a 64-bit architecture, as well as a 32-bit architecture without
CONFIG_COMPAT_32BIT_TIME, handling this command is a mistake,
and the kernel should return an error".

         Arnd