Boot sector for ext2

Boot sector for ext2

[Martin Rosenau]

Hello everyone.

I am new to GRUB development.

I wrote a tool I wish to publish under GPL that may be integrated into 
GRUB instead of publishing as separate tool:

Background: In a multi-OS-environment it is sometimes not possible 
installing GRUB on the MBR (Windows Vista has problems then!)
Installing GRUB on an ext2 partition (instead of on the MBR) often 
requires "block lists" which often do not work.

I wrote a boot sector that is capable to search a file on the ext2 
partition by file name (not by inode or block number etc...) and load 
it. Because the entire code is quite small it fits into the boot sector 
and "block lists" are not required.

This would also allow to use different "core.img" files (e.g. one 
booting Linux and one booting Memtest) when booting GRUB from a chain 
loader (e.g Windows' boot menu).

I did not have the possibility to fully test the tool, yet.

Are you interested in integrating this tool into GRUB?

Have a nice weekend.

Martin

Re: Boot sector for ext2

[Colin Watson]

On Sat, May 21, 2011 at 09:31:14AM +0200, Martin Rosenau wrote:
> I wrote a tool I wish to publish under GPL that may be integrated
> into GRUB instead of publishing as separate tool:
> 
> Background: In a multi-OS-environment it is sometimes not possible
> installing GRUB on the MBR (Windows Vista has problems then!)
> Installing GRUB on an ext2 partition (instead of on the MBR) often
> requires "block lists" which often do not work.
> 
> I wrote a boot sector that is capable to search a file on the ext2
> partition by file name (not by inode or block number etc...) and
> load it. Because the entire code is quite small it fits into the
> boot sector and "block lists" are not required.
> 
> This would also allow to use different "core.img" files (e.g. one
> booting Linux and one booting Memtest) when booting GRUB from a
> chain loader (e.g Windows' boot menu).

Hi,

Thanks for your work.  However, doesn't this overlap with what the
"ntldr-img" GRUB extras module (originally based on part of GRUB4DOS)
already does?  Its purpose is to be small enough that it can be booted
from the Windows boot loader, which may only be able to load 16 sectors;
it supports reading a named file from a handful of file systems,
including ext2 and NTFS.  It's commonly shipped along with GRUB; for
example, Debian and Ubuntu ship it.

Admittedly, ntldr-img will not fit into 512 bytes, so if that's what
your code does then it does occupy a slightly different space.

Regards,

-- 
Colin Watson                                       [cjwatson@ubuntu.com]

Re: Boot sector for ext2

[Grégoire Sutre]

On 05/21/2011 09:31 AM, Martin Rosenau wrote:

> Background: In a multi-OS-environment it is sometimes not possible
> installing GRUB on the MBR (Windows Vista has problems then!)
> Installing GRUB on an ext2 partition (instead of on the MBR) often requires
> "block lists" which often do not work.
>
> I wrote a boot sector that is capable to search a file on the ext2 partition
> by file name (not by inode or block number etc...) and load it. Because the
> entire code is quite small it fits into the boot sector and "block lists"
> are not required.

I find this very interesting.  The two alternatives that exist currently
(or, at least, that I know of), namely (a) installing in the MBR (+ the
following sectors), or (b) using block-lists, have well-known shortcomings.

With your solution, one could simply write the boot sector in an ext2
partition's boot record, and put GRUB files in the ext2 filesystem.
Whatever is in the MBR would then simply chainload the ext2 partition.
Is this correct?

Grégoire

Re: Boot sector for ext2

[Martin Rosenau]

Grégoire Sutre wrote:
> I find this very interesting.  The two alternatives that exist currently
> (or, at least, that I know of), namely (a) installing in the MBR (+ the
> following sectors), or (b) using block-lists, have well-known shortcomings.
> 
> With your solution, one could simply write the boot sector in an ext2
> partition's boot record, and put GRUB files in the ext2 filesystem.
> Whatever is in the MBR would then simply chainload the ext2 partition.
> Is this correct?

Yes. This is how it should work.

Martin