linux-kernel - Re: [PATCH] Input: uinput - Add UI_SET

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Date:   Mon, 2 Dec 2019 14:54:56 -0800
From:   Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Pali Rohár <pali.rohar@...il.com>,
        linux-input@...r.kernel.org,
        Bluez mailing list <linux-bluetooth@...r.kernel.org>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Logan Gunthorpe <logang@...tatee.com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        Kirill Smelkov <kirr@...edi.com>
Subject: Re: [PATCH] Input: uinput - Add UI_SET_UNIQ ioctl handler

On Mon, Dec 2, 2019 at 11:36 AM Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
>
> On Mon, Dec 02, 2019 at 07:53:40PM +0100, Pali Rohár wrote:
> > On Monday 02 December 2019 09:54:40 Dmitry Torokhov wrote:
> > > On Mon, Dec 02, 2019 at 09:47:50AM +0100, Pali Rohár wrote:
> > > > On Sunday 01 December 2019 17:23:05 Dmitry Torokhov wrote:
> > > > > Hi Pali,
> > > > >
> > > > > On Sun, Dec 01, 2019 at 03:53:57PM +0100, Pali Rohár wrote:
> > > > > > Hello!
> > > > > >
> > > > > > On Wednesday 27 November 2019 10:51:39 Abhishek Pandit-Subedi wrote:
> > > > > > > Support setting the uniq attribute of the input device. The uniq
> > > > > > > attribute is used as a unique identifier for the connected device.
> > > > > > >
> > > > > > > For example, uinput devices created by BlueZ will store the address of
> > > > > > > the connected device as the uniq property.
> > > > > > >
> > > > > > > Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> > > > > >
> > > > > > ...
> > > > > >
> > > > > > > diff --git a/include/uapi/linux/uinput.h b/include/uapi/linux/uinput.h
> > > > > > > index c9e677e3af1d..d5b7767c1b02 100644
> > > > > > > --- a/include/uapi/linux/uinput.h
> > > > > > > +++ b/include/uapi/linux/uinput.h
> > > > > > > @@ -145,6 +145,7 @@ struct uinput_abs_setup {
> > > > > > >  #define UI_SET_PHYS                _IOW(UINPUT_IOCTL_BASE, 108, char*)
> > > > > > >  #define UI_SET_SWBIT               _IOW(UINPUT_IOCTL_BASE, 109, int)
> > > > > > >  #define UI_SET_PROPBIT             _IOW(UINPUT_IOCTL_BASE, 110, int)
> > > > > > > +#define UI_SET_UNIQ                _IOW(UINPUT_IOCTL_BASE, 111, char*)
> > > > > >
> > > > > > I think that usage of char* as type in _IOW would cause compatibility
> > > > > > problems like it is for UI_SET_PHYS (there is UI_SET_PHYS_COMPAT). Size
> > > > > > of char* pointer depends on userspace (32 vs 64bit), so 32bit process on
> > > > > > 64bit kernel would not be able to call this new UI_SET_UNIQ ioctl.
> > > > > >
> > > > > > I would suggest to define this ioctl as e.g.:
> > > > > >
> > > > > >   #define UI_SET_UNIQ         _IOW(_IOC_WRITE, UINPUT_IOCTL_BASE, 111, 0)
> > > > > >
> > > > > > And then in uinput.c code handle it as:
> > > > > >
> > > > > >   case UI_SET_UNIQ & ~IOCSIZE_MASK:
> > > > > >
> > > > > > as part of section /* Now check variable-length commands */
> > > > >
> > > > > If we did not have UI_SET_PHYS in its current form, I'd agree with you,
> > > > > but I think there is benefit in having UI_SET_UNIQ be similar to
> > > > > UI_SET_PHYS.
> > > >
> > > > I thought that ioctl is just number, so we can define it as we want. And
> > > > because uinput.c has already switch for variable-length commands it
> > > > would be easy to use it. Final handling can be in separate function like
> > > > for UI_SET_PHYS which can look like same.
> > >
> > > Yes, we can define ioctl number as whatever we want. What I was trying
> > > to say, right now users do this:
> > >
> > >     rc = ioctl(fd, UI_SET_PHYS, "whatever");
> > >     ...
> > >
> > > and with UI_SET_UNIQ they expect the following to work:
> > >
> > >     rc = ioctl(fd, UI_SET_UNIQ, "whatever");
> > >     ...
> >
> > And would not following definition
> >
> >   #define UI_SET_UNIQ _IOW(_IOC_WRITE, UINPUT_IOCTL_BASE, 111, 0)
> >
> > allow userspace to call
> >
> >   rc = ioctl(fd, UI_SET_UNIQ, "whatever");
> >
> > as you want?
>
> OK, so what you are saying is that we can have whatever in the size
> portion of ioctl number and simply ignore it in the driver (and I do not
> think we need to do any of "UI_SET_UNIQ & ~IOCSIZE_MASK" really).
> While this would work, I am not sure it is the best option as I think
> we'd have to comment extensively why we have arbitrary number in place
> of the size.
>
> And we still do not really save anything, as we still have to go through
> compat ioctl handler (since we have it already) and it is very simple to
> add a case for UI_SET_UNIQ there...
>
> Thanks.
>
> --
> Dmitry

Since the compat handling already exists for UI_SET_PHYS, I think I
would prefer to go with the simpler solution of just duplicating that
for UI_SET_UNIQ. Next patch is coming with that change.

Thanks
Abhishek