Re: some semi-technical GRUB questions

[Jochen Hoenicke]

On Thursday, 10. January 2002 08:49, Simon Kitching wrote:
>
> 1. where does the stage1.5 get written to on a hard-drive?
>    (*) if using FFS or ReiserFS, and there is sufficient space in
> the "boot area"
>        reserved by these filesystems, is that space used? Is it the
> first choice
>        location?

If you use the "setup" command it first tries to embed it in the root 
file system (if it's Reiser or FFS), then in the partition where it 
is installed to.  If grub is installed to MBR, it tries to embed it 
in the following gap before first partition.

>    (*) does GRUB check the partition table to look for "gaps"
> between partitions,
>        and assume that they are available for use? If so, what
> kinds of gaps qualify (eg would space after the last partition be
> used?) [a note in the existing doc implies that the first partition
> *often* starts at (cyl=0,head=1,sector=0) rather than immediately
> after the MBR (cyl=0,head=0,sector=1), but not always]

Only the gap after the MBR is used if it is big enough and stage1 is 
embedded into the MBR.

>    (*) if there aren't any gaps between partitions, then what does
> grub do? does it resize partitions? does it print an error message
> & give up? does it write the stage1.5 into the filesystem
> containing the boot partition?

If embedding stage1.5 doesn't succeed at all it loads stage2 directly 
from the file system with a block list.  This can be dangerous but 
normally a file doesn't move.

> 2. What are the implications of "defrag"-type operations on a
> filesystem containing a stage2 (or a stage1.5 if these do get
> stored within filesystems)?
>    Considering the stage1 or stage1.5 has a "block-list" pointing
> to it, I presume this is unhealthy...

You have to install grub again...

> 3. Is there a copy of the "multiboot standard" document anywhere?

I think there's a section in the manual.

> 4. Where does GRUB get its file-system implementations from? Are
> they taken from linux/hurd/bsd, or rewrites? If taken from a kernel
> release, do they need to be modified to run in the GRUB environment
> (eg if grub doesn't have
>    paging enabled)? Related issue: will GRUB support booting to
> ext3/jfs/jffs/etc
>    partitions?

They are hand written for grub.  Only read-only support is there and 
the methods to implement are very few.

I leave the remaining questions open...


  Jochen