[LEDE-DEV] Older u-boot mangles UBI from ubinize 1.5.2

[Daniel Golle]

Hi J,

On Thu, Aug 11, 2016 at 06:15:32AM -0700, J Mo wrote:
> 
> 
> On 08/11/2016 05:31 AM, Daniel Golle wrote:
> > That's what I told you in the previous mail, removing the rootfs=
> > parameter from the dts should do the trick, because you just cannot
> > mount a ubi device (which is a character device in Linux) with a
> > block-based filesystem (like squashfs). This cannot and won't ever
> > work and you could either leave it to OpenWrt/LEDE's auto-probing to
> > figure out what to do based on the rootfs type (non-ubifs vs. ubifs)
> > or append even more board- and filesystem-specific crap to your cmdline
> > such as ubiblock=... root=/dev/ubiblock0_1 (however, that then won't
> > work for ubifs, thus the auto-probing patches).
> 
> ... OH!
> 
> Well, I needed some extra intellectual clubbing to catch on.
> 
> NOW I remember reading the UBI docs, about glubi, the fact that volumes are
> char devices, and I even seem to remember some ALL CAPS red size-20+ text at
> the top of the page saying something about it.
> 
> Tomorrow I'll go read the docs again, because I know I remember reading that
> you could put a RO-squashfs in a UBI volume.  I just need to have it mounted
> the right way.

Exactly. However, this makes mounting a UBIFS volume entirely different
from mounting a volume with any other (read-only) filesystem which
needs a ubiblock device (gluebi has been deprecated in favour of
ubiblock) to be created and subsequently mounted.
The idea of the auto-probing patches [1] was to keep things filesystem-
agnostic, ie. allow for either a single read-write UBIFS rootfs or any
read-only filesystem (e.g. squashfs) which needs ubiblock and have a
UBIFS read-write overlay on top.
In this way, all you have to take care of is *not* to have any rootfs=
or ubi* parameters in your kernel cmdline and all the rest should
happen automagically.


Cheers


Daniel