Bootloader question

Mitch Bradley wmb at
Tue Jun 2 22:12:04 EDT 2009

> From what I've read on the
> wiki, JFFS2 is here only because OFW doesn't know how to use UBIFS.

Don't believe everything you read on a wiki.

As Peter Robinson says, JFFS is used because it was the only viable 
alternative at the time we were doing the initial development.  UBIFS 
did not become viable from a technical standpoint until the middle of 
last year, and OLPC's software team hasn't had the resources to fully 
test UBIFS and do the very substantial amount of work necessary to 
change over to it.  OFW would not have to change, because ...

>> No idea, but you can use a small /boot partition with jffs2 (or ext2)
>> which is enough to boot the kernel and then have a ubifs root file
>> system.

OFW has included support for partitioned NAND since the first production 
shipments, dating back to January 2008.  The idea is to have a small 
boot partition that can be in any format that OFW supports - JFFS2, 
ext2, FAT, or even a .zip archive.  JFFS2 is just fine on a small 
partition; the scan time for a few MB is negligeable. I have been 
lobbying for such a structure for about 2 years now, but never managed 
to get enough traction among the OS people to actually implement it in 
the XO software distribution.  The OFW support for this is known to 
work, as debxo uses it.

> I'd also be interested to know what is required to add support for new
> filesystems to OFW. ext4 now has the option to run without a journal
> which gives it the advantage that ext2 had over ext3 with a lot of the
> other improvements that come with ext4. I wonder what would be
> required to add support for it and the likes of ubifs?

I'm thinking about ext4, but I must confess that my experience with ext2 
has been pretty frustrating. The ext2/3 on-disk format has sprouted many 
new features over time.  Supporting people who plug in disks that are 
formatted with the latest fancy feature, then complain that an old 
firmware release fails to work with it, is difficult.

I am more inclined to insist that the boot partition must be formatted 
with a stable format - stable in the sense that the spec rarely changes.

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