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A tempest in a tty pot

A tempest in a tty pot

Posted Jul 29, 2009 17:36 UTC (Wed) by BrucePerens (guest, #2510)
In reply to: A tempest in a tty pot by michaeljt
Parent article: A tempest in a tty pot

The console must work during boot, when the kernel panics, etc.


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A tempest in a tty pot

Posted Jul 29, 2009 18:23 UTC (Wed) by michaeljt (subscriber, #39183) [Link]

I didn't talk about moving the console driver into user space, just the tty driver - I actually suggested that the tty driver could use the console driver.

A tempest in a tty pot

Posted Jul 29, 2009 18:31 UTC (Wed) by BrucePerens (guest, #2510) [Link]

Yeah, you don't really need the tty discipline for the console. But you do need the ANSI terminal to framebuffer code, and the SysReq code for the keyboard, and both of those have to work when the kernel isn't running processes. So, you end up not having too much that can be moved out of the kernel.

A tempest in a tty pot

Posted Jul 29, 2009 19:35 UTC (Wed) by michaeljt (subscriber, #39183) [Link]

Why the ANSI terminal to framebuffer code? I would have thought that simple line printing, along with a couple of ioctls for moving the cursor and selecting colours would be enough. And of course all the virtual terminal stuff is not needed either for printing kernel messages.

A tempest in a tty pot

Posted Jul 29, 2009 19:41 UTC (Wed) by BrucePerens (guest, #2510) [Link]

Well, the color is set with ANSI codes. And there's a lot of code that backspaces over itself and reprints while indicating something in process.

So. you end up with a reasonably large piece of function-duplicating code if you split the kernel console and a more elaborate user console.

A tempest in a tty pot

Posted Jul 29, 2009 19:57 UTC (Wed) by nix (subscriber, #2304) [Link]

And you *do* need the line discipline code for booting on serial consoles,
serial logging of panics, and so on.

A tempest in a tty pot

Posted Jul 30, 2009 8:18 UTC (Thu) by michaeljt (subscriber, #39183) [Link]

Does that require the line discipline code to be in the kernel, or would running it from the boot loader to set up the line suffice?

A tempest in a tty pot

Posted Jul 30, 2009 8:21 UTC (Thu) by michaeljt (subscriber, #39183) [Link]

Not that I can immediately think of a single argument as to why having the code in the boot loader would be better than having it in the kernel...


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