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Moving the Linux Kernel Console To User-Space
jones_supa sends this quote from Phoronix:
"David Herrmann has provided an update on his ambitious initiative to kill off the Linux kernel console. Herrmann has long been working on making the Linux kernel CONFIG_VT option unnecessary for providing a Linux console by punting it off to user-space. The Linux kernel VT console hasn't been changed much in the past two decades and Herrmann is hoping to see it replaced with a user-space solution he's been developing that would allow for multi-seat support, a hardware-accelerated console, full internalization, and other features."
The idea is to replace a kernel functionality with few features and several crucial limitations with a user space solution that is fully-fledged. The fully-fledged solution is not what you want to have inside the kernel, therefore taking the console to user space.
The need for this arose primarily with the introduction of kernel mode setting etc. Before these advances, the console would somewhat be lame by definition. Now it is much more viable to have a nice console even without a windowing system and that opens new applications to a user-space console.
E.g. look at Terminology. It is a virtual terminal emulator from the Enlightenment guys, built on the EFL core libraries. It works with David Herrmanns patches, without X11 or any display server!
http://www.youtube.com/watch?v=AD-BJThtNnc (here run within X)
Compare this to the basic kernel console. It could replace it if David's work gets through.
When you are on the X console, all keys are handled by X, including the Ctrl-Alt-F1 (that's why if you lock up X badly, even Ctrl-Alt-F1 won't work, although you may still be able to remotely log in and fix things; assuming you have sshd or something equivalent running, of course). However switching back to X11 with Ctrl-Alt-F7 (or whereever your current X session is) is handled by the console.
That is why you have Ctrl+Alt+SysRq+R ( http://en.wikipedia.org/wiki/Magic_SysRq_key )
The VT console has been "hardware accelerated" under x86/VGA for years. You don't think it's actually copying memory line for line when it needs to scroll the screen, do you? No, it's incrementing the VGA register that tells it what memory address to start drawing text from.
QNX, the real-time message passing operating system now owned by Blackberry, does all "console" handling in user space. They've done that for years. That's because, in the embedded world, you can't assume the target machine has a console, or even a serial port.
When you build a QNX boot image for an embedded system, you can add any programs you want to be available as soon as the system boots. All device drivers are in user space, so that's how the initial set of drivers gets loaded. You can also load applications that way. Having a file system is optional. If necessary, all software can be in a ROM. This allows scaling down to small embedded devices.
A serial console program is available, and is loaded into most systems that have a serial port. There are other options for systems that don't have a serial port, like connecting it to a network.
There's also a system logger. It's common to have the system logger log to some network destination elsewhere, so problems out at Pumping Station 42 are reported to the control center far away.
Linux has tried to emulate this architecture. More drivers are in user space. But in Linux that was an afterthought, and it shows.