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SubjectRe: Devfs, was Re: Migrating to larger numbers
Date
Catalin Muresan wrote:
> By 'lilo' I meant /sbin/lilo not the boot loader

I see, sorry for suggesting that you got that wrong.

> and the option
> LABEL=boot should be added to lilo's config file /etc/lilo.conf so then
> /sbin/lilo would translate this option into root=301 (for ex.), a kernel
> boot option.

Hmm, this may actually a bit confusing, although it would cover most
cases of practical relevance, but there's more to it - see below.

> Thinking again maybe the kernel should understand something like
> BOOTLABEL=boot instead of root=301, but I think it's rather ugly (then lilo
> would not me modified).

I'd favour this approach, because it defers label to device translation to
boot time. So if you swap disks, it will still pick the right one, and not
the one that was right before the swap.

Now the limitation here is of course that LILO and the kernel are normally
on exactly this disk, so as soon as you swap it, LILO becomes a problem
anyway. Nevertheless, if someone puts LILO and the kernel at a safe place
somewhere else, then the boot-time translation is the behaviour they are
likely to expect.

Basically, the main problem is that disk swapping or more advanced means
to improve availability (RAID, etc.) do not work terribly well with
hard disk-based boot loaders. The obvious work-around is to have a copy
of the boot loader on each disk that may be used for booting, or to use a
boot floppy.

When using LILO, the problem is aggravated by the need to include at least
one kernel in the set of files that need to be replicated. Other boot
loaders somewhat avoid this problem by being able to read the file system,
so they can boot any kernel from any disk. However, the problem they're
facing is that they either have to require the use of a small set of file
system features (e.g. ext2 only), or they need to track most of the
developments in the area of RAID, LVM, and new file systems, which sounds
like a software engineering nightmare to me.

Maybe we should start specifying the "Linux 2000 PC", with a built-in 16
MB Flash EPROM "disk" for storing boot loader and kernels ;-)

- Werner

--
_________________________________________________________________________
/ Werner Almesberger, ICA, EPFL, CH werner.almesberger@ica.epfl.ch /
/_IN_R_131__Tel_+41_21_693_6621__Fax_+41_21_693_6610_____________________/
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