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