On Mon, Apr 01, 2019 at 09:16:22AM +0200, Hans de Goede wrote:
> Hi,
>
> On 01-04-19 05:05, Peter Hutterer wrote:
> > On Sat, Mar 30, 2019 at 02:37:30PM +0100, Hans de Goede wrote:
> > > Almost all modern mice use HID. For buttons 1 - 3 the order of left /
> > > right / middle specified in the HUT matches with the BTN_LEFT, BTN_RIGHT
> > > and BTN_MIDDLE order of the evdev code defines since the HUT does not
> > > specify any meaning for button usages >= 4 the HID input driver simply
> > > maps buttons to BTN_LEFT + (number - 1).
> > >
> > > In practice on most mice which have more then 3 buttons, usage 4 is
> > > used for the back(ward) button and usage 5 for the forward button.
> > >
> > > This means that these buttons generate an input_event code of 0x113 resp.
> > > 0x114, which looking at the old defines maps to BTN_SIDE and BTN_EXTRA.
> > >
> > > Under X these are mapped to buttons 8 resp. 9; and under wayland the
> > > input_event code is passed through unmodified. Apps, e.g. Firefox both
> > > when running as Wayland client under GNOME3 and when running under Xorg,
> > > correctly interpret these as back and forward.
> > >
> > > So we've back and forward buttons generating BTN_SIDE and BTN_EXTRA,
> > > which the apps then interpret as BTN_BACK and BTN_FORWARD, rather then as
> > > BTN_SIDE and BTN_EXTRA (which have no clear meaning).
> > >
> > > I find this all very confusing, this commit tries to remove the confusion
> > > by deprecating the old defines and adding new defines which assign labels
> > > to the 0x113 - 0x116 input_event codes which match how they are actually
> > > used today.
> > >
> > > Note there are no functional changes here, after this userspace will
> > > see the exact same input_event codes as before, this purely about
> > > assigning a human-readable label to these codes which matches with how
> > > they are actually being used.
> >
> > there is a small functional change, primarily seen by debugging tools: where
> > button names are resolved to strings, only one name is returned (at least by
> > libevdev). So things like libevdev_event_code_get_name(EV_KEY, BTN_EXTRA)
> > will now return "BTN_FORWRD" instead of "BTN_EXTRA". This has a potential to
> > break whatever is consuming those strings.
>
> True, but that is actually intentional. I believe the main consumer of these
> strings are humans and the whole reason to fix the string is to stop confusing
> humans, starting with myself. I'm not fully specialized on input, but I've
> done my fair share of input work, so if this confuses me it will certainly
> confuse others.
>
> > Not sure what the impact of this will be though. It's already the case for
> > other buttons and I've mostly shrugged it off as niche case not to worry
> > about. But we're talking about buttons that almost every modern mouse has,
> > so it's slightly less niche now.
>
> True, but I believe most consumers of these events will either be X-clients
> or Wayland clients. I'm pretty sure X-clients are not seeing these strings,
> I would also not expect Wayland clients to somehow end up using the
> libevdev_event_code_get_name() output, but I'm slightly less sure there:
>
> [hans@shalem ~]$ sudo dnf repoquery --whatrequires 'libevdev.so.2()(64bit)'
> dolphin-emu-0:5.0-27.fc30.x86_64
> dolphin-emu-nogui-0:5.0-27.fc30.x86_64
> evemu-0:2.7.0-9.fc30.x86_64
> evemu-libs-0:2.7.0-9.fc30.x86_64
> gnome-battery-bench-0:3.15.4-10.fc30.x86_64
> libevdev-devel-0:1.6.0-2.fc30.x86_64
> libevdev-utils-0:1.6.0-2.fc30.x86_64
> libinput-0:1.12.6-3.fc30.x86_64
> libinput-utils-0:1.12.6-3.fc30.x86_64
> libmanette-0:0.2.2-1.fc30.x86_64
> libratbag-ratbagd-0:0.9.904-2.fc30.x86_64
> weston-0:5.0.91-1.fc30.x86_64
> weston-0:6.0.0-1.fc30.x86_64
> xorg-x11-drv-evdev-0:2.10.6-4.fc30.x86_64
> xorg-x11-drv-synaptics-legacy-0:1.9.1-3.fc30.x86_64
>
> I do not believe that either libinput or the 2 xorg-x11-drv
> pkgs pass along strings to clients.
>
> I will leave judging if this is a problem for ratbagd up to you.
ratbagd doesn't expose this but maybe some debug messages, same for
libinput and evemu. weston doesn't use that function, so it's good.
evdev/synaptics are fine too. This is less of an issue for the primary users
of evdev (they have the code after all) but the secondary users.
For example, the libinput-gestures project parses libinput debug-events
output (against my advice I would add). That output contains the button
names. libinput-gestures doesn't care about button names but tools like it
can break if the button name changes. I'm not aware of any tools that care
about those specific button numbers.
Anyway, this is more an explanation that there *may* be side-effects but we
probably won't know until we run into them, if ever.
> As for the other I assume dolphin-emu is using this
> for joysticks. Which just leaves weston as a potential problem
> which IMHO itself is a bit of a niche-case.
> So I do not think this will cause much of a problem.
>
> > > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > > ---
> > > Documentation/input/event-codes.rst | 2 +-
> > > drivers/hid/hid-debug.c | 6 +++---
> > > drivers/input/mousedev.c | 8 ++++----
> > > include/uapi/linux/input-event-codes.h | 13 ++++++++++++-
> > > 4 files changed, 20 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
> > > index b24b5343f5eb..db52b96e7a83 100644
> > > --- a/Documentation/input/event-codes.rst
> > > +++ b/Documentation/input/event-codes.rst
> > > @@ -422,7 +422,7 @@ should be used to report when the tool is in contact with the tablet.
> > > BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
> > > button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
> > > BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
> > > -meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
> > > +meaningful buttons, like BTN_FORWRD, unless the button is labeled for that
> >
> > I haven't thought of a better name yet, but using BTN_FORWRD is bound to
> > introduce bugs, especially when BTN_FORWARD still resolves. I don't think
> > that name is a good idea but I don't have a better suggestion yet.
>
> Good point about the typos my plan for the kernel is to add #ifndef __KERNEL__
> around the compat defines once all users are moved over.
good, but not enough. the kernel is easiest here because you could literally
just add a script to a test suite to make sure it doesn't use BTN_FORWARD.
It's all the userspace that'll introduce typos.
> > Thought of the day: if HID doesn't have any meaning, is it really worth
> > changing these names based on what you hope a client interprets it as?
> > would a more generic naming scheme that admits this is just button 4 be
> > better? BTN_HID_4 or something?
>
> The HUT spec may not say anything about this (note I did not check the
> gazillion errata I really wish they would just fold those into an
> updated version), but Microsoft writes the following about this and it
> is reasonable to expect mice vendors to follow this (and in practice they do):
> https://docs.microsoft.com/en-us/windows-hardware/drivers/hid/keyboard-and-mouse-hid-client-drivers
>
> "Buttons 4 & 5 on are mapped to WM_APPCOMMAND messages and correspond to App_Back and App_Forward."
BTN_APP_FORWARD and BTN_APP_BACK then? seems obvious enough and is a lot
easier to visually identify than a missing A in FORWRD.
> All in all I think this will be worth the trouble. As the commit messages
> of the patches moving over in kernel users of the old defines show, there
> are already several in kernel drivers which are likely using the old defines
> wrong, as they assume that BTN_FORWARD and BTN_BACK actually work as advertised
> and I almost made the same mistake myself, so IMHO we really need to fix this
> and the sooner we fix this the better.
I noticed you left BTN_TASK in the #defines, any specific reason for that
over using BTN_EXTRA3 for that one?
Cheers,
Peter
> > > purpose on the device.
> > > For new hardware, both INPUT_PROP_DIRECT and INPUT_PROP_POINTER should be set.
> > > diff --git a/drivers/hid/hid-debug.c b/drivers/hid/hid-debug.c
> > > index ac9fda1b5a72..45b56f933fd1 100644
> > > --- a/drivers/hid/hid-debug.c
> > > +++ b/drivers/hid/hid-debug.c
> > > @@ -855,9 +855,9 @@ static const char *keys[KEY_MAX + 1] = {
> > > [BTN_6] = "Btn6", [BTN_7] = "Btn7",
> > > [BTN_8] = "Btn8", [BTN_9] = "Btn9",
> > > [BTN_LEFT] = "LeftBtn", [BTN_RIGHT] = "RightBtn",
> > > - [BTN_MIDDLE] = "MiddleBtn", [BTN_SIDE] = "SideBtn",
> > > - [BTN_EXTRA] = "ExtraBtn", [BTN_FORWARD] = "ForwardBtn",
> > > - [BTN_BACK] = "BackBtn", [BTN_TASK] = "TaskBtn",
> > > + [BTN_MIDDLE] = "MiddleBtn", [BTN_BACKWRD] = "BackwardBtn",
> > > + [BTN_FORWRD] = "ForwardBtn", [BTN_EXTRA1] = "ExtraBtn1",
> > > + [BTN_EXTRA2] = "ExtraBtn2", [BTN_TASK] = "TaskBtn",
> > > [BTN_TRIGGER] = "Trigger", [BTN_THUMB] = "ThumbBtn",
> > > [BTN_THUMB2] = "ThumbBtn2", [BTN_TOP] = "TopBtn",
> > > [BTN_TOP2] = "TopBtn2", [BTN_PINKIE] = "PinkieBtn",
> > > diff --git a/drivers/input/mousedev.c b/drivers/input/mousedev.c
> > > index 412fa71245af..7504e854900f 100644
> > > --- a/drivers/input/mousedev.c
> > > +++ b/drivers/input/mousedev.c
> > > @@ -238,16 +238,16 @@ static void mousedev_key_event(struct mousedev *mousedev,
> > > case BTN_RIGHT: index = 1; break;
> > > case BTN_2:
> > > - case BTN_FORWARD:
> > > + case BTN_EXTRA1:
> > > case BTN_STYLUS2:
> > > case BTN_MIDDLE: index = 2; break;
> > > case BTN_3:
> > > - case BTN_BACK:
> > > - case BTN_SIDE: index = 3; break;
> > > + case BTN_EXTRA2:
> > > + case BTN_BACKWRD: index = 3; break;
> > > case BTN_4:
> > > - case BTN_EXTRA: index = 4; break;
> > > + case BTN_FORWRD: index = 4; break;
> > > default: return;
> > > }
> > > diff --git a/include/uapi/linux/input-event-codes.h b/include/uapi/linux/input-event-codes.h
> > > index 7f14d4a66c28..f11ce5d2c228 100644
> > > --- a/include/uapi/linux/input-event-codes.h
> > > +++ b/include/uapi/linux/input-event-codes.h
> > > @@ -355,11 +355,22 @@
> > > #define BTN_LEFT 0x110
> > > #define BTN_RIGHT 0x111
> > > #define BTN_MIDDLE 0x112
> > > +#define BTN_BACKWRD 0x113
> > > +#define BTN_FORWRD 0x114
> > > +#define BTN_EXTRA1 0x115
> > > +#define BTN_EXTRA2 0x116
> > > +#define BTN_TASK 0x117
> > > +
> > > +/*
> > > + * DEPRECATED: Do not use!
> > > + * These old defines are to not break the compilation of user code ONLY.
> > > + * Over time they have grown to be incorrect. Almost all modern mice with
> > > + * back / forward buttons generate 0x113 for back and 0x114 for forward.
> > > + */
> > > #define BTN_SIDE 0x113
> > > #define BTN_EXTRA 0x114
> > > #define BTN_FORWARD 0x115
> > > #define BTN_BACK 0x116
> > > -#define BTN_TASK 0x117
> > > #define BTN_JOYSTICK 0x120
> > > #define BTN_TRIGGER 0x120
> > > --
> > > 2.21.0
> > >
