Bootloader rootfs

Andy Green andy at openmoko.com
Thu Mar 20 11:18:42 CET 2008


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Somebody in the thread at some point said:
> Andy Green wrote:
>> I wonder if we need to get away from this enforced minimalism there, it
>> is sort of U-Boot thinking.
> 
> :-) The basic idea is to have a small core system. Whether it's in
> an initramfs or a rootfs shouldn't really make such a big difference,
> since you should want to load most of that core system anyway. For
> big extra stuff, one can always go to a regular rootfs, be it one
> made just for booting or the "real" rootfs.

If there is a graphical basis for it as we can actually imagine (because
we can hand it off to someone else to do now it isn't in its queer
U-Boot world), one only pulls the graphical stuff one wants at the time
from the filesystem.  So it is not "all one" if we use initramfs and
force ourselves to pull everything before boot completes.  Same goes for
libs and apps that may run off a menu, we never touch them unless they
run if it is a rootfs.

>> Why don't we treat the alternate kernel and rootfs as made up of pieces
>> from the normal packages (and libc / libs!),
> 
> Yup, that's how it should be. If the libraries get too bloated,
> there's always uclibc, which seems to be quite well integrated into
> OE.

Some bloat is OK if we don't have to pull everything to even get booted,
ie, we use a rootfs.  I like uclibc because I used it before with good
results, but we shouldn't consider it if it isn't used with our main
packages.

We should stop this alternate boot filesystem being a project of its own
and just make it another (smaller) kind of buildhost rootfs you can get
and modify at a package level, again it means the guys that work with
normal rootfs and packages can take care of it for us.  Sure it won't be
anything like the main rootfs in size and complexity, but we (well,
others) can build it the same from the same packages, etc and it is off
our plate safely, is maintained properly, etc.  And since it is just
normal Linux it doesn't make trouble for the guys that actually deal
with it then.

>> That will also further regularize how you work with this alternative
>> kernel + rootfs -- just copy files in the filesystem on the device, not
>> regenerate magic initramfs images on a host.
> 
> Yes, that would be ideal. I'm a bit afraid of library bloat, though.
> But we can start with a general system and optimize later, if
> necessary.

Good, so it means a decent sized (16MB?) rootfs for the alternate boot
if I understood we synced up that far.

- -Andy
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