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

[Gergely Kiss]

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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