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

On 6/10/06, Antonino A. Daplas [off-list ref] wrote:

quoted

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.

quoted

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