Re: [PATCH 5/5] VT binding: Add new doc file describing the feature

Jon Smirl
2006-06-10T23:44:57Z

On 6/10/06, Antonino A. Daplas <adaplas@gmail.com> wrote:
> > I may be looking at the problem a little differently. I see the
> > drivers like fb, vga, etc as registering with the console and saying
> > they are capable of providing console services. I then see the console
> > system as opening one of the registered devices. A driver is free to
> > register/unregister whenever it wants to as long as it isn't open by
> > the console system. Console can only open one driver at a time.
>
> No, this isn't true. You can have multiple console drivers active,
> that's why you have a first and last parameter in take_over_console().
> Thus at boot time, the system driver will take consoles 0 - 63.
> Later on when a driver loads, it can take over consoles 0 - 7, leaving
> consoles 8 - 63 to the system driver.
>
> To put it another way, console drivers can register for consoles 0 - 63,
> but the user may choose to use it only for consoles 0 - 7.
>
> This is another reason for the system driver, it makes the unbinding
> behavior predictable. Without a system driver, guessing which driver
> replaces the just unbound one may become just a tad bit confusing for
> the typical user.

I find the whole console/tty layer to be quite confusing to talk
about. I am mixing up console as in where printk goes and console the
video card login device. The part about making everything equal was
directed towards the printk output device.

I see now that you can have tty0-7 assigned to a different console
driver than tty8-63.
Why do I want to do this?
Why do we need 64 predefined tty devices?

Googling around the only example I could find was someone with a VGA
card and a Hercules card. They setup 8 consoles on each card.

> > Over time it would nice if these all merged to a single
> > interchangeable interface. I would really like to be able to
> > dynamically switch to serial/net while debugging a video driver. Is
> > there some fundamental reason why these can't be merged?
>
> It's already possible to redirect the system messages to two different
> console classes, ie with the boot parameter:
>
> console=tty0,ttyS0 /* direct output to VT and serial console */
>
> And you can already choose the console you want by adjusting /etc/inittab.

How can I change where printk are going at run-time? I didn't know you
could do that.

--
Jon Smirl
jonsmirl@gmail.com