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    SubjectRe: [RFC][PATCH] input: Introduce device information ioctl
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    On Tuesday 07 December 2010, Kay Sievers wrote:
    > On Tue, Dec 7, 2010 at 10:16, Dmitry Torokhov <dmitry.torokhov@gmail.com> wrote:
    > > Hi Henrik,
    > >
    > > On Tue, Dec 07, 2010 at 08:25:26AM +0100, Henrik Rydberg wrote:
    > >> Today, userspace sets up an input device based on the data it emits.
    > >> This is not always enough; a tablet and a touchscreen may emit exactly
    > >> the same data, for instance, but the former should be set up with a
    > >> pointer whereas the latter does not need to. Recently, a new type of
    > >> touchpad has emerged where the buttons are under the pad, which changes
    > >> handling logic without changing the emitted data. This patch introduces
    > >> a new ioctl, EVIOCGDEVINFO, which allows userspace to extract information
    > >> about the device resulting in proper setup.
    > >
    > > If we agree that the new ioctl is suitable we'llalso need to wireit up
    > > through sysfs. Also, can we keep all definitions to INPUT_ namespace?
    >
    > Please don't add new ioctls which are not extensible. The ioctl should
    > carry the length or the version of the structure it asks for, so it
    > can be extended in the future. Sysfs should be good enough for such
    > interface though.

    Please never add any ioctls that have a version or length field!

    Ideally ioctls should have only scalar arguments, not structures,
    so I'd recommend splitting it into two, so you can read type and
    capability parameters separately.

    Arnd


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