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

[Flávio Silveira]

On 16/12/2014 11:23, Gergely Kiss wrote:
> Hi Rafał,
>
> please allow me to comment on your 2nd point as I was the one who
> recently published the patch to make extroot functionality work with
> UBIFS.
>
> "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"."
>
> That's correct.
>
> "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)?"
>
> 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?
>
>
> Thanks,
> Gergely
>
>
> On 16 December 2014 at 11:00, Rafał Miłecki <zajec5 at gmail.com> wrote:
>> I've spent few hours today trying to understand extroot. I've failed :(
>>
>> Of course I was trying to use wiki pages:
>> http://wiki.openwrt.org/doc/howto/extroot
>> http://wiki.openwrt.org/doc/uci/fstab
>>
>> 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)?
>>
>> --
>> Rafał
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Hi,

   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

Regards,
   Flavio
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