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Notes on condor_kbdd
March 13, 1999
The purpose of the condor_kbdd is to monitor keyboard and mouse activity on
a given machine's console. The console is simply the physical mouse and
keyboard attached to the named computer. Xterms and remote X connections
are not currently monitored.
Periodiclly the condor_kbdd for user activitiy (the mouse moves, mouse's
buttons go up or down, keys go up or down), if user activity is detect, it
sends a simple UDP packet to the condor_startd, notifing it that the
machine's idle time is now 0. During normal use circumstances, this will
result in 1 packet per interval time being sent to the startd if the machine
is being used constantly.
On Unix, we accomplish the task of monitoring via two seperate tasks: first
connecting to the display, and second, monitoring XEvents.
In order to connect to the display, we must have permission to connect. In
condor environments where daemons are not running as root, this is
accomplished with a simpl XOpenDisplay(). This call may fail if the person
logged into the machine has enabled security on the display, or if xdm is
running. If it fails, the condor_kbdd will be ineffectual. To get around
this problem, it is preferable to run the daemon as user root. The daemon
will then attempt to figure out who is logged in and masquered as this person
in order to open the display. This is accomplished by cycling through
utmp entries and optional XAUTHORITY_USERS config param and setting the
XAUTHORITY environment variable. See the methods XInterface::NextEntry(),
XInterface::TryUser(), and XInterface::Connect() in XInterface.cpp for more
Once connected to the display, we walk the tree of windows, notifing
X that we want to receive KeyPress events that are bound for this window.
This code is in XInterface::SelectEvents(). The specifics of how this works
are not well known as they were stolen from xautolock.
Every poll interval, XInterface::CheckActivity() is called. This function
checks to see if any XEvents have come in that would indicate activity,
and looks for new windows that may have been created. New windows are
setup for event catching. In order to watch the state of the mouse, the
condor_kbdd simply keeps the last coordinates of the mouse in memory and
every poll interval checks to see if the coordinates are different. If they
are, the mouse has obviously moved. Although it may be possible to thwart
this detection scheme, the probabilities are extrodinarily low.
There are some race conditions that are introduced with a window popping up
very quickly and being destroyed right away. When this happends, we start
to select events on the new window that has been destroyed and end up
causing an X IO error. This error is caught in CatchIOFalseAlarm().
Unfortunately, X assumes that the process wants to exit after an error, so
it calls exit(). We don't want this, so we simply long jump back into our
code. Very messy.
Finally, the daemon sends a command to the startd if there has been activity.
The command is of type X_EVENT_NOTIFICATION. There is no included data.
Currently, we attempt to attach to display localhost:0.0. This should be
unix:0.0. I see no reason why this shouldn't work, but I have no committed
it as I have not had time to test it.
The window race condition is really messy and needs a better solution. Perhaps
a c++ exception, or maybe something even more clean.
It would be nice if the condor_kbdd monitored remote X connections as well.
In have no plan of attack for this at this time.