Re: boot loader that can read from partition?

On 20 Oct 2006 23:02:42 -0700 Kaz Kylheku <kkylheku@xxxxxxxxx> wrote:
| phil-news-nospam@xxxxxxxx wrote:
|> Where would this map file be? One thing I want to avoid is the boot
|> loader storing anything it needs in any filesystem. I want to be able
|> to zero-out and reformat every filesystem and still have the boot loader
|> be able to bring up a kernel.
|
| But you obviously can't zero-out and reformat every partition. The boot
| loader and kernel(s) have to live somewhere, right? That somewhere can
| be a small filesystem partition, which has the boot loader there, its
| configuration file, and kernel images. You can mount this under, hmm,
| /boot.
|
| Hey, wait a minute! :)

Yes, the kernel must be somewhere. But the program that will put the
kernel in won't be running under Linux or anything that understand any
Linux filesystem. When I described that the kernel would be written
to the partition "as if I did" the "dd" command, I meant that some
program would be writing the sectors linearly, not that it would be
running under Linux.


| But you know, if you zero out every filesystem, what is there to boot?
| You can't do anything if you don't have a root filesystem. If you have
| a way to create a root filesystem in a partition, then at the same time
| you can stick a vmlinux kernel image into its root directory. The boot
| loader that understands filesystems can then just find it. If the name
| hasn't changed, that loader doesn't even have to be reconfigured.

There will be a root filesystem. With the "early user space" feature of
the kernel, it's approximately like having an initrd built into the kernel
image itself (not separately loaded) ... though various namespace setups
normally done by the kernel are now pawned off to the first user space
program being run (which is not a problem).


| So what you can do is have a dedicated partition which just holds Grub
| and its configuration file. No kernels.

Why not kernels? If you're going to have a filesystem, why not put the
kernel there, too? That's actually what I do now, though with LILO, not
GRUB. And it also happens to be a smallish root filesystem, too, for
rescue purposes. But this next project involves not having any filesystem
at all.


|> At the moment, my kernel resides in a partition that is a smallish (256MB)
|> system, along with lilo and many recovery tools. That partition is not
|> used during normal system operation which uses other full size partitions.
|> I would like to be able to easily rebuild that extra system partition but
|> not clobber the kernel when doing so. Hence the need for another partition.
|
| Right. A tiny partition with the boot loader, smallish partition with
| recovery tools, then bigger partitions. The tiny one with the
| bootloader can boot into everything using filesystem access to grab the
| respective kernels from there, and passing the right root=... option to
| that kernel.

What I have now is unrelated to this next project, aside from it being a
learning and illustration example. What I need is a boot loader that can
load a raw kernel image from a raw partition. I can't explain what this
is about, but I know that having such a boot loader "leaps the barrier"
to making these new ideas work.

I asked for such a boot loader because it seemed appropriate to do that
before writing my own (which I don't want to do). It seems enough people
have joined in this thread that I can probably assume no such boot loader
exists. I would have thought it would be the very first kind of boot
loader long before anything that deal with filesystems one way (LILO) or
the other (GRUB). What was around before LILO to load Linux from a hard
drive?

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2006-10-21-1821@xxxxxxxx |
|------------------------------------/-------------------------------------|
.

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