[OpenWrt-Devel] Current state of extroot, how to use it, what about ubi(fs)

Rafał Miłecki zajec5 at gmail.com
Tue Dec 16 05:00:33 EST 2014

I've spent few hours today trying to understand extroot. I've failed :(

Of course I was trying to use wiki pages:

1) Main question
Is the following sentence true at all?
> The configuration of extroot is very simple and is done entirely in /etc/config/fstab.

It seems that /etc/init.d/fstab uses "block umount" and "block mount"
only. I was reading the source code (fstools-2014-12-15/block.c) and
it seems that "block mount" doesn't really handle extroot at all.

I think some kind of extroot support is provided in "block extroot",
but I don't fully understand it. It seems to be looking for partitions
"rootfs" and then "rootfs_data" ignoring whatever is set in
/etc/config/fstab. If "mount extroot" is really supposed to be used,
is there any way to point some external device (without MTD
partitions) as extroot? I got confused.

2) UBI and UBIFS support

I guess it's too new to be documented and I don't understand it much
from the code. It seems that if there isn't "rootfs" MTD partition,
then the code will look for "rootfs" UBI volume. The same applies to
the "rootfs_data".
But what if my serial flash contains "rootfs" + "rootfs_data"
partitions and I still want to use some UBI volume on another flash
(NAND one)?

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