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15-410 Project 4 Extended Console

Here is what we would like to see in terms of virtual consoles.

Virtual Consoles

  • What "virtual consoles" means is that the single physical screen and keyboard are multiplexed by the operating system (that's you) so that it looks as if there are multiple instances of each one. Output routines such as print() will paint a virtual screen, which may or may not be visible, and keyboard scancodes will result in characters being available on various keyboard queues at various times.

  • From the user's point of view, there should be multiple independent text consoles, and pressing the Tab key on the keyboard should switch the screen and keyboard "immediately" from one virtual console to another (by "immediately" we mean that this should happen promptly--not after the next timer interrupt, after the next readline() completes, etc.).

  • Threads belonging to a task share a virtual console. Each newly created task will begin using the same virtual console as its parent task.

  • If you wish to use a different color combination for each virtual console, they must all be reasonable.

  • A new system call, int new_console(void), should determine if a request for a new console is supportable, and, if so, should allocate an unused console and switch all further console I/O of the calling task to the new virtual console.

  • If any thread in a thread family has a console I/O operation pending or in progress, new_console() should fail.

  • If too many virtual consoles are in use, new_console() may fail. You should support at least 8 virtual consoles.

  • Once a virtual console has no more threads or proceses associated with it, it should be deleted from the Tab key rotation after the user has had a chance to view the contents once (it might be friendly for the kernel to somehow indicate to the user that this is the last viewing of the console and optionally for the kernel to require a confirmatory keypress).

  • If nobody ever calls new_console(), the operation of the console/keyboard system should be as it was for P3. Also, user code should have no way of observing it is not running on a P3 kernel without virtual consoles (aside from the behavior of new_console()).

    In case you're wondering, the number of lines available on the screen is not deemed to be a "P3 kernel property"--in theory a "P3 kernel" could have any number of lines on the console as long as the system call interface behaved correctly.

Utility Program

The update area contains a program called new_shell which will use the new_console() system call to launch a shell in a new console window.

Context

By the way, the Linux machines in the clusters support virtual consoles...press Control-Alt-F1, Control-Alt-F2, etc. Those virtual consoles are persistent rather than being created and deleted as we are suggesting for P4.

[Last modified Monday April 24, 2006]