Re: I/O permissions for V86 tasks (Enhanced V86 Mode)?

Ian Collier (imc@comlab.ox.ac.uk)
Tue, 21 Jul 1998 14:08:31 +0100 (BST)


On Fri, 17 Jul 1998 12:38:22 -0800, Kendall Bennett said:
> Sounds interesting. I am not sure I understand the need to put VBE
> services into the kernel, rather than leaving them in user space and
> simply relying on the v86() system call to handle the V86 portions of
> the code.

Firstly, because it is nice to have this handled via a device file in
/dev; I don't know of a way to pass ioctls to user-space drivers. Using
/dev allows the driver to emulate /dev/fb and therefore get software support
(e.g. an X server) without having to rewrite the software.

Secondly, because when I started I didn't believe it was possible in
user space (clearly I've been proven wrong (-: ). The fact that Linux
preserves page 0 helps - I didn't know that before.

> > So far no one has offered me an easier way to do it (though one person
> > did suggest I should run it in protected mode in a 16-bit code segment -
> > doesn't sound to me like that would work too well...).

> This wont work because the BIOS will be doing real mode specific
> segment arithmetic and stuff that simply wont work in 16-bit
> protected mode.

Well, if the only thing it does with segments is to load 0x40 into a segment
register this can easily be dealt with by creating a valid segment with this
descriptor (in fact I think it's already been done for the APM code in 2.1).

imc

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.altern.org/andrebalsa/doc/lkml-faq.html