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Add links to documentation
[[Category:Plans]]
[[Category:Plans]]
== Problem ==
Doing C/R of an X-application is not currently supported due to a simple fact -- all X-apps hold connections to X-server and, sometimes, have a video-card-related device opened as a file or even mapped as a virtual memory region.
== Connection to X-server ==
X-server connection is a typical TCP (or Unix) socket that CRIU [[TCP connection|can handle]] by itself. And, in theory, we could dump an X-application and restore it on the same machine, making the X-server "think" that nothing has changed. Unfortunately, this is not what "checkpoint and restore an X-app" is expected to be. The expectation is when after checkpoint the app window(s) disappear from the screen and after restore they pop-up on it again. In order to achieve this CRIU needs to "talk" to the X-server no both checkpoint and restore sides.
On the checkpoint node we need to get the list of associated with the application resources that X-server maintains in memory to serve the application X-needs.
On the restore node we need to put the resources in question back to the X-server to make the app window(s) pop-up on the screen again (in simple words).
Both tasks require some (maybe deep) knowledge/understanding of the X-server and X-protocol.
== Video card device ==
CRIU can handle some devices, in particular ttys and virtual /dev/null|zero|etc. ones. For a "more real" device the situation is close to what has just been described -- a device is likely to have some state regarding the application referring it via file descriptor or a memory mapping. This state also has to be handled somehow.
== See also ==
[https://www.x.org/wiki/Documentation/ Xorg Documentation]
[https://www.x.org/releases/X11R7.7/doc/libX11/libX11/libX11.html Xlib - C Language X Interface]