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

Antonino A. Daplas
2006-06-11T01:16:13Z

Jon Smirl wrote:
> On 6/10/06, Antonino A. Daplas <adaplas@gmail.com> wrote:
>> > 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?
>>
>> Multi-head. I can have vgacon on the primary card for tty0-7,
>> fbcon on the secondary card for tty8-16.
>
> That's what I thought, I couldn't see any other reason. The kernel
> doesn't support input from multiple users so multihead can only be
> used by a single user.
>
> Does anyone use single user multihead on current systems? The kernel
> doesn't have code in it to initialize secondary VGA cards. What modern
> non-VGA hardware does this work on?

matroxfb supports multihead and fbcon already has this feature for a
long time, ie you can bind /dev/fb0 to tty0-3 and /dev/fb1 to tty4-6.
And there are definite users because I happen to break this feature once
and I got rained with complaints :-)

>
> If this feature doesn't work on current hardware, could it be dropped?
> It would make binding to the vt system much simpler if only one driver
> could be bound at a time. Anything we do to make that system simpler
> would benefit everyone.

You can't drop something that's already in the kernel and has users, well,
the binding part at least. What we don't currently have is the fine-grained
control and because of the reason's you mentioned, I said that it's for the
future.

(Note1: fbcon already has support to selectively bind/unbind drivers
to specific tty's, using the con2fbmap utility.)

So what we have is control for wholescale binding and unbinding of
drivers, which essentially results in only 1 driver loaded at one time.

(Note2: fbcon already has an option to determine what range of vc's to
control, as a kernel boot parameter, so we can't just drop something
that's already supported by one driver at least. Though I know of no one,
including myself, who uses this feature.)

>
> At some future point I would like to explore pushing the VT system out
> to user space where it becomes much easier to make it multi-user and
> multi-head. If you do that, something like a single user, in-kernel
> system management console makes more sense.

Yes.

Tony