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

Rafał Miłecki zajec5 at gmail.com
Tue Dec 16 13:28:03 EST 2014

On 16 December 2014 at 16:30, Imre Kaloz <kaloz at openwrt.org> wrote:
> On Tue, 16 Dec 2014 16:06:27 +0100, Gergely Kiss <mail.gery at gmail.com>
> wrote:
>> On 16 December 2014 at 14:39, Flávio Silveira <fggs at terra.com.br> wrote:
>>> On 16/12/2014 11:23, Gergely Kiss wrote:
>>>> I'm not sure I understand what you mean here. Are there any devices
>>>> out there with multiple flash chips on-board? As far as I know, UBI
>>>> cannot work on top of block devices (eg. USB flashes, SD cards), only
>>>> raw flash chips so I can't really imagine what exact use-case you
>>>> mean. Could you please clarify?
>>>   I think this is where this discussion started and Rafal explains a bit
>>> more about the hardware:
>>> https://lists.openwrt.org/pipermail/openwrt-devel/2014-December/029717.html
> Rafal, what about mtdconcat?

That would be nice because I could use space available on the serial
flash. So far I assumed to ignore that extra ~10 MiB and focus on NAND

However I'm not sure if this will be possible without heavy changes.

I have rootfs_data (JFFS2) partition on serial flash. I would need to
concat it with my UBI partition on NAND flash.
1) I'm afraid it may be complex to change the way OpenWrt treats
rootfs_data. It's coded in many places.
2) Concanation has to be handled in the kernel. There isn't any DT
driver I could use for bcm53xx. Guess I'd need to write once
3) I have no idea if UBI can work well on concan-ated partition. In
theory yes, but in practice? UBI cares pretty much about wearing I

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