GSoC: CD-ROM booting options

GSoC: CD-ROM booting options

[Alex Roman]

Hello,

Last week I started working on my GSoC project for GRUB2: CD-ROM boot
support. I wanted to make sure I understand what we want to support in
GRUB2.

Do we want to be able to boot the computer from GRUB2 installed on a
medium (whatever it may be), then be able to boot from a CD  (in
whatever mode - emulation or no emulation)?

Do we also want to be able to boot the computer through the BIOS from
a CD on which GRUB2 was installed and continue booting from the CD
(like GRUB legacy does)?

Do we want to support both?

Personally, I think both are important to support, but I want to see
what the majority of developers and users think we should support.


Thanks in advance!

-- 
Alex Roman <alex.roman@gmail.com>

Re: GSoC: CD-ROM booting options

[Marco Gerards]

"Alex Roman" <alex.roman@gmail.com> writes:

Hi Alex,

[...]

> Do we want to be able to boot the computer from GRUB2 installed on a
> medium (whatever it may be), then be able to boot from a CD  (in
> whatever mode - emulation or no emulation)?

Yes.

> Do we also want to be able to boot the computer through the BIOS from
> a CD on which GRUB2 was installed and continue booting from the CD
> (like GRUB legacy does)?

Yes.

> Do we want to support both?

Yes.

> Personally, I think both are important to support, but I want to see
> what the majority of developers and users think we should support.

Just focus on one thing first.  I think booting from a BIOS that
supports CDROMs already won't be too hard.

--
Marco

Re: GSoC: CD-ROM booting options

[Jeroen Dekkers]

At Mon, 04 Jun 2007 17:10:53 +0200,
Marco Gerards wrote:
> 
> "Alex Roman" <alex.roman@gmail.com> writes:
> 
> > Personally, I think both are important to support, but I want to see
> > what the majority of developers and users think we should support.
> 
> Just focus on one thing first.  I think booting from a BIOS that
> supports CDROMs already won't be too hard.

I think booting installation and live CDs directly from the BIOS will
be the most used way to boot a CD, so I guess support for that is the
most important. And it indeed shouldn't be that hard.

Jeroen dekkers

Re: GSoC: CD-ROM booting options

[Alex Roman]

On 04/06/07, Jeroen Dekkers <jeroen@vrijschrift.org> wrote:
> At Mon, 04 Jun 2007 17:10:53 +0200,
> Marco Gerards wrote:
> >
> > "Alex Roman" <alex.roman@gmail.com> writes:
> >
> > > Personally, I think both are important to support, but I want to see
> > > what the majority of developers and users think we should support.
> >
> > Just focus on one thing first.  I think booting from a BIOS that
> > supports CDROMs already won't be too hard.
>
> I think booting installation and live CDs directly from the BIOS will
> be the most used way to boot a CD, so I guess support for that is the
> most important. And it indeed shouldn't be that hard.
>

Sounds good.

I think I will start by focusing on "no emulation" mode. ISOLINUX
seems to be using this mode and it makes use of EDD 3.0 INT 13
extensions to read from the CD. The only problem I see here is if we
boot from a BIOS that doesn't support EDD 3.0. We may not be able to
read from the CD in that case, so we would have to use emulation mode.

In any case, I'll keep you all posted on the progress I make.

-- 
Alex Roman <alex.roman@gmail.com>

Re: GSoC: CD-ROM booting options

[adrian15]

> Do we want to be able to boot the computer from GRUB2 installed on a
> medium (whatever it may be), then be able to boot from a CD  (in
> whatever mode - emulation or no emulation)?
> 
> Do we also want to be able to boot the computer through the BIOS from
> a CD on which GRUB2 was installed and continue booting from the CD
> (like GRUB legacy does)?
> 
> Do we want to support both?
> 
> Personally, I think both are important to support, but I want to see
> what the majority of developers and users think we should support.

	Although a lot of people want you to begin with the second option and
although it's a good thing for an hipothetical super grub2 disk... I
want to remind you what's the okuji thought about this:

=======
>> My name is Alex Roman and I have been selected as a Summer of Code
>> > > student for the GRUB2 project. I will be adding CD-ROM booting
>> > > functionality to GRUB2.
> >
> > Welcome! Cdrom booting funcionality for grub2 is a good piece of news.
> >
>> > > The first stage of the project will attempt to use BIOS calls
>> > > to achieve this functionality (which is, of course, dependent on the
>> > > BIOS's capabilities, standards compliance, etc.).
> >
> > Ok. That's how it works in Grub legacy I suppose.

Nope. This is a different thing. This is a new feature which is not
present in GRUB Legacy.

Although people often mistake this, booting a CD from GRUB is quite
different from booting a GRUB installed into a CD. GRUB Legacy has the
latter feature, but not the former one.

GRUB 2 needs to support both cases, but I prefer to see something not
present in GRUB Legacy implemented in GRUB 2 first.

=======

But do as you want, maybe it is better to begin with the easiest task
and then doing the more difficult task.

adrian15

Re: GSoC: CD-ROM booting options

[Alex Roman]

On 05/06/07, adrian15 <adrian15@raulete.net> wrote:
> GRUB 2 needs to support both cases, but I prefer to see something not
> present in GRUB Legacy implemented in GRUB 2 first.

Good point... In any case there's some commonality between the two
cases and for now I'm working to see if I can read some ElTorito data
structures from a bootable CD... Which brings me to the question:

Is it possible to call int 13h functions from a GRUB2 module? If yes,
what is the (preferred?) way to do it?


Thanks in advance!

-- 
Alex Roman <alex.roman@gmail.com>

Re: GSoC: CD-ROM booting options

[Vesa Jääskeläinen]

Alex Roman wrote:
> On 05/06/07, adrian15 <adrian15@raulete.net> wrote:
>> GRUB 2 needs to support both cases, but I prefer to see something not
>> present in GRUB Legacy implemented in GRUB 2 first.
> 
> Good point... In any case there's some commonality between the two
> cases and for now I'm working to see if I can read some ElTorito data
> structures from a bootable CD... Which brings me to the question:
> 
> Is it possible to call int 13h functions from a GRUB2 module? If yes,
> what is the (preferred?) way to do it?

You need to add new kernel thunk(s) to grub2/kern/i386/pc/startup.S and
then make them jump to 16b real mode and then return back to protected
mode. There are lots of examples in that file. Then make proper include
file for your calls (most likely you can add it to existing one in this
include file grub2/include/grub/i386/pc/biosdisk.h).

I would suggest to make testing command that accesses those kernel
thunks. This way it is easier to test out those API calls.

Re: GSoC: CD-ROM booting options

[Alex Roman]

That's what I plan on doing... I want to write a module that for now
just allows me to test various int 13h calls, look at their return
values and get a general idea of how things work.

Thanks for the idea Vesa!


Cheers!

On 07/06/07, Vesa Jääskeläinen <chaac@nic.fi> wrote:
> Alex Roman wrote:
> > On 05/06/07, adrian15 <adrian15@raulete.net> wrote:
> >> GRUB 2 needs to support both cases, but I prefer to see something not
> >> present in GRUB Legacy implemented in GRUB 2 first.
> >
> > Good point... In any case there's some commonality between the two
> > cases and for now I'm working to see if I can read some ElTorito data
> > structures from a bootable CD... Which brings me to the question:
> >
> > Is it possible to call int 13h functions from a GRUB2 module? If yes,
> > what is the (preferred?) way to do it?
>
> You need to add new kernel thunk(s) to grub2/kern/i386/pc/startup.S and
> then make them jump to 16b real mode and then return back to protected
> mode. There are lots of examples in that file. Then make proper include
> file for your calls (most likely you can add it to existing one in this
> include file grub2/include/grub/i386/pc/biosdisk.h).
>
> I would suggest to make testing command that accesses those kernel
> thunks. This way it is easier to test out those API calls.
>
>
>
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>


-- 
Alex Roman <alex.roman@gmail.com>