SHM in synaptics provided two functionalities: run-time configuration and hardware monitoring.
run-time configuration works by having the driver configuration exposed as a shared memory segment and letting another process change this state. hw monitoring works by dumping the hw state read from the device into the shared memory and then having another process print this state.
synclient was the default UI (though syndaemon used SHM as well).
X Server 1.6 introduced input device properties, a generic way to attach information to input devices. The information can be attached by drivers or clients, and both drivers and clients are notified about changed values. Hence, it's a good vehicle for device-specific configuration.
- synaptics 1.0 had input device property support in the driver, but SHM configuration is still available.
- synaptics 1.1 had synclient and syndaemon use input device properties by default, but SHM configuration is still available.
- synaptics 1.2 (current release) has configuration through SHM removed from both the driver and synclient/syndaemon and the SHM area is not writable by the user anymore.
The following GUI tools use properties:
- gnome-mouse-properties + gnome-settings-daemon
- gsynaptics (merely a wrapper around synclient). discontinued, see gpointing-device-settings.