Comment 17 for bug 9441

Kirill: I am commenting as the member of the VirtualBox development team in charge of keyboard handling in Linux. My guess is that the "locate pointer" tool places a "passive grab" [1] on the control key. What this means if it is correct is that as of the point when the grab is placed no other application can see the control key being pressed or released unless the tool explicitly allows it (I presume it doesn't); however they can still (usually) see combinations including the control key, such as Ctrl-Scroll in Frederik's example above. Certainly VirtualBox relies on being able to spot individual keypresses and releases and doesn't try to monitor key combinations to work around this sort of thing: we take the point of view that if the user wants to take keys away from us for other purposes they should know what they are doing, and we don't want to add complexity to deal with it and risk creating bugs for other people. If there were a nice way of spotting passive grabs by other applications we might warn the user, but I don't know of any way other than trying to grab every key ourselves to see which ones we can't get.

[1] http://tronche.com/gui/x/xlib/input/XGrabKey.html