[OpenWrt-Devel] Some standard partition name for extra user data?

Rafał Miłecki zajec5 at gmail.com
Sun Dec 7 10:18:13 EST 2014

On 7 December 2014 at 16:11, John Crispin <blogic at openwrt.org> wrote:
> On 07/12/2014 16:05, Hauke Mehrtens wrote:
>> On 12/07/2014 01:30 AM, Rafał Miłecki wrote:
>>> I've bcm53xx device which has two usable flashes:
>>> 1) SPI serial flash for CFE + firmware + NVRAM
>>> 2) NAND flash for extra data
>>> Because of general design of OpenWrt firmware my image contains two
>>> partitions: kernel and rootfs (SquashFS). Automatically rootfs_data
>>> (JFFS2) is created right after rootfs.
>>> I wanted to make space on NAND flash also usable for OpenWrt. Do you
>>> have any advice on that?
>>> 1) The coolest idea would be to use some LVM solution, but I don't
>>> think we have anything like this ready in OpenWrt. Or do we? AFAIK UBI
>>> itself can't work as LVM (can't use blocks from several MTD
>>> partitions)?
>>> 2) So I was thinking about simply registering that NAND partition with
>>> some name we could make common across OpenWrt targets. Something like
>>> "extra_data" or whatever you prefer. User would need to mount it and
>>> use a proper directory for storing his data. Is there anything like
>>> this in any other target?
>>> Yet another solution could be to ignore this few MiB space on serial
>>> flash and simply use NAND for rootfs_data. But this would:
>>> 1) Waste some minor space on SPI serial flash
>>> 2) Would require hacking partitioner to don't create rootfs_data
>>> 3) Hacking UBI a bit I guess
>> Hi,
>> I assume these device are loading the kernel from serial flash by default.
>> Have you looked at extroot:
>> http://wiki.openwrt.org/doc/howto/extroot
>> This is used to place the root file system on an external storage.
>> Hauke
> HI,
> extroot is the wrong pattern for 2 flash setups.
>>> 1) Waste some minor space on SPI serial flash
> how big is spi / nand

SPI serial flash is 16 MiB
NAND is 128 MiB

>>> 2) Would require hacking partitioner to don't create rootfs_data
> huh ? ubifs ?

I have to store "rootfs" on SPI serial due to CFE flashing method.
Since "rootfs" is there, OpenWrt will create "rootfs_data" right after
it. So with a partition "rootfs_data" on NAND I'd end up with two
"rootfs_data" partitions.
Since this is a device with SPI serial flash, I don't use UBI there
(it's squashfs + jffs2 right now).

>>> 3) Hacking UBI a bit I guess
> sound like a wrong assumption no idea why you think ubi wont work on
> your flash

I guess I was thinking about a way to create UBI partition on NAND
flash, create UBI volume + format it. Since this is a separated flash,
I couldn't use ubinize for that.
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