Bug#369917: xserver-xorg-input-mouse: Gets number of buttons wrong, even if Option "Buttons" specified

[Daniel Dawson]

Package: xserver-xorg-input-mouse
Severity: normal

Version: 1:1.0.4-2

Using a Logitech MX500 mouse (USB), I find that the server is getting the
number of buttons wrong (too high). This happens even if I explicitly tell it
how many buttons there are. Here is the relevant section of the log showing the
server reading one value, then declaring a different one:

(**) Generic Keyboard: Core Keyboard
(**) Option "Protocol" "standard"
(**) Generic Keyboard: Protocol: standard
(**) Option "AutoRepeat" "500 30"
(**) Option "XkbRules" "xorg"
(**) Generic Keyboard: XkbRules: "xorg"
(**) Option "XkbModel" "pc104"
(**) Generic Keyboard: XkbModel: "pc104"
(**) Option "XkbLayout" "us"
(**) Generic Keyboard: XkbLayout: "us"
(**) Option "XkbOptions" "compose:rwin"
(**) Generic Keyboard: XkbOptions: "compose:rwin"
(**) Option "CustomKeycodes" "off"
(**) Generic Keyboard: CustomKeycodes disabled
(**) Option "Protocol" "Auto"
(**) Configured Mouse: Device: "/dev/input/mice"
(**) Configured Mouse: Protocol: "Auto"
(**) Option "CorePointer"
(**) Configured Mouse: Core Pointer
(**) Option "Device" "/dev/input/mice"
(**) Option "Buttons" "10"
(==) Configured Mouse: Emulate3Buttons, Emulate3Timeout: 50
(**) Option "ZAxisMapping" "9 10"
(**) Configured Mouse: ZAxisMapping: buttons 9 and 10
(**) Configured Mouse: Buttons: 14
(II) XINPUT: Adding extended input device "Configured Mouse" (type: MOUSE)
(II) XINPUT: Adding extended input device "Generic Keyboard" (type: KEYBOARD)
(--) Configured Mouse: PnP-detected protocol: "ExplorerPS/2"
(II) Configured Mouse: ps2EnableDataReporting: succeeded

-- System Information:
Debian Release: testing/unstable
  APT prefers testing
  APT policy: (990, 'testing')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.16-ddawson
Locale: LANG=en_US, LC_CTYPE=en_US (charmap=ISO-8859-1)


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Bug#369917: xserver-xorg-input-mouse: Gets number of buttons wrong, even if Option "Buttons" specified

[Drew Parsons]

> I find that the server is getting the number of buttons wrong (too
> high).
> 
> (**) Configured Mouse: ZAxisMapping: buttons 9 and 10
> (**) Configured Mouse: Buttons: 14

For reference this button count appears to be coming from mouse.c l.706,

/* get maximum of mapped buttons */
for (i = pMse->buttons-1; i >= 0; i--) {
int f = ffs (pMse->buttonMap[i]);
if (f > pMse->buttons)
pMse->buttons = f;
}


That is, the original value is being reset to the value of 
ffs(pMse->buttonMap[i]), where this is larger.  The larger number
appears to be ("actual" number)+4.  At a guess, the extra 4 buttons
correspond to the X- and Y-axes, with the normal mouse wheel occupying
the Z-axis.

ffs is defined or referred to in /usr/include/xorg/compiler.h
and ../xf86_libc.h (xserver-xorg-dev).  A low level definition is found
in /usr/include/asm-generic/bitops/ffs.h, "find first bit set"

I suspect this is not actually a bug.

Drew


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