Re: boot loader that can read from partition?

On Sat, 14 Oct 2006 16:40:44 -0700 John Reiser <jreiser@xxxxxxxxxxxx> wrote:
| phil-news-nospam@xxxxxxxx wrote:
|> On Sat, 14 Oct 2006 10:14:29 -0700 John Reiser <jreiser@xxxxxxxxxxxx> wrote:
|> | phil-news-nospam@xxxxxxxx wrote:
|> |> Is there a boot loader than can read a kernel in from a raw partition?
|
|> PC x86, DOS style partitions.
|
|> | For i386 with the usual BIOS and DOS-style ("basic") partitions:
|> |
|> | http://bitwagon.com/ftp/mbr03.tgz
|> | http://bitwagon.com/ftp/e2boot4c.tgz
|
|> Is there any way to combine these? Since I don't need the ext2 code
|> at all, and loading from a partition is always purely sequential,
|> would it be possible to get the partition boot loader to load from
|> the partition directly? It should just be a matter of reading the
|> partition table to get the partition loadcation that mbr03 knows to
|> do, load the image sequentially from start to end of the partition
|> (it may be more sectors than needed) by simple sector increment by
|> one, and then pass control to the kernel? Would it fit? Since at
|> least sector 0 is never assigned to a partition, could additional
|> unassigned sector be used to cheat for space on the boot loader?
|
| The request "boot from a raw disk partition" [i.e., a marked extent
| of contiguous sectors] is somewhat strange. Unless there will be
| _no_ filesystem of any kind after boot, then put the kernel and initrd
| into a filesystem. Using the two .tgz above works for ext2/ext3.
| Syslinux works for FAT. loadlin also works on FAT, and will even
| boot linux from inside a running DOS. The OS/2 boot loader runs
| with upto 15 extents; you might try it.

For loading from index sectors I have LILO. For loading from files in
a filesystem, I have GRUB. Either of these should have been able to
load from a partition mostly because it should be easy. Or what would
be hard about it?


|> I don't have sufficient x86 assembly knowledge plus the spare machine
|> needed to experiment with coding x86 assembly at the boot loader level
|> to be able to put this together myself.
|
| Use qemu. http://fabrice.bellard.free.fr/qemu/
|
| Explain enough about the need to use a raw disk partition, in order to
| convince other hackers to join you. Until then, qemu + {syslinux,
| loadlin, mbr03+e2boot4c, possibly others} is what you get.

It's a system that will be dynamically built each time it boots up.
But it also needs to be able to reboot in certain cases where it is
not rebuilt for whatever reason. I can't rely on a filesystem being
buildable. This also involves a small flash disk.

This probably should have been the basic way to boot a system from
early on. It would have, for example, avoided the need to store an
array of indexes by LILO. It would have been easy to update the
kernel. With two partitions, there could also be a fallback. I do
not think it is strange at all. It's booting the KISS way. But if
people don't like partitions, then I guess that might be the real
reason.

Does QEMU pass a whole disk device from the real machine into the
virtual machine it emulates, at a different position ... e.g. can
it make all of /dev/hdc appear as IDE primary master and then run
a boot loader that uses BIOS for initial I/O?

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-10-14-1958@xxxxxxxx |
|------------------------------------/-------------------------------------|
.

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