Plasma and the Screensaver ========================== There are three main pieces to the screensaver picture, two of which involve plasma. first is lockprocess, which manages the other two. second is the [k|x]screensaver binaries which just draw pretty pictures. third is plasma-overlay, which does the plasma stuff. lockprocess ----------- This process manages plasma and the screensaver binaries, and ensures that once the screen is locked it *stays* locked until proper authentication is provided. It provides the unlock dialog too. If a screensaver or plasma-overlay crashes or becomes unresponsive, lockprocess will keep going, ensuring that a locked screen stays locked and can still be unlocked by the user. It's as small as possible to keep the chances of it itself crashing very small. The screensaver binaries are brought in via XEmbed, while communication with plasma-overlay happens over dbus. lockprocess also filters all keyboard and mouse events, passing them on to plasma-overlay as necessary. if it suspects that plasma-overlay is dead (ie. dbus failure), it won't pass on events, ensuring that the user never ends up with an unresponsive screensaver. plasma-overlay -------------- This process is a plasma shell; it has a corona and a simple view, and loads its own containment. The containment used by plasma-overlay is very basic; just a customcontainment with a cashew and applet handles. the user can add applets, but not containments. there's configuration for transparency if you have compositing, or wallpaper if not (random wallpaper slideshow is my poor-man's-screensaver). all configuration and applet add/remove are disabled when the screen is locked. it communicates with lockprocess over dbus. lockprocess will send it into an idle mode after a while (where any events trigger the unlock dialog, and plasma-overlay uses a different transparency setting), and tell it to go into active mode when there's activity again. when an unlock action in plasma is activated, plasma-overlay asks lockprocess for permission, and lockprocess will ask the user for their password (or whatever other authentication method). when the screen is locked, plasma-overlay offers two actions to the user: leave screensaver and configure widgets. the first is what you'd expect; you enter your password and all of lockprocess goes away, letting you back into your desktop. the second is more like unlocking widgets in plasma-desktop: it brings you into configuration mode where you can add, remove and configure widgets. this config mode can also be reached from the screensaver kcm module. from config mode you can exit at any time without entering a password; you can also re-lock the screen, of course. if lockprocess vanishes from dbus, plasma-overlay will assume that it missed a signal to quit and will commit suicide. :) this is intentional; I got sick of dbus race conditions leaving me with a plasma-overlay hanging around if I moved the mouse just after the screensaver began to run. security --------- Plasmoids on the screensaver obviously present a security risk. this is being minimized as described in the security document. what makes it interesting is that we're less concerned with malicious plasmoids and more with malicious (or mischievous) users; a locked screen left unattended should not end up with goatse on it, or files deleted. Future Work ----------- * Multi-screen support would be awesome * Plasmify the unlock dialog (either by using plasma theming or by having plasma-overlay run it)