Grow UBI device?

[Richard Weinberger]

On Thu, Oct 10, 2013 at 10:17 AM, Artem Bityutskiy <dedekind1 at gmail.com> wrote:
> Wolfgang, people already answered you, and frankly I did not read all
> the answers :-) But here is my brief version.
>
> On Tue, 2013-10-08 at 21:28 +0200, Wolfgang Denk wrote:
>> I'm looking for a clever way to migrate devices (in the field) from
>> JFFS2 to UBI/UBIFS.  In the end result, I want to have single UBI
>> device (which covers the whole NAND chip) with several volumes used
>> with UBIFS.  Unfortunately I must keep some of the existing data.
>
> And I guess there is no temporary storage where you could copy JFFS2
> files, re-format the flash, and copy the files back.
>
>> It would be nice if I could start with a UBI device that is smaller
>> than the NAND, so I can keep an existing MTD partition with a JFFS2
>> file system.
>
> You mean that on the existing systems, you already have an extra MTD
> partition, or you somehow can create one.
>
> Then you want to UBI/UBIFS-format the extra partition. Then copy
> required JFFS2 files there. And then kill JFFS2 partitions and "merge"
> them with the extra partition, and end up with UBI/UBIFS covering all
> the space.
>
>>  After copying the data from JFFS2 to a UBIFS volume, I
>> would like to free and reuse the space of this JFFS2 partition.
>
> OK, sounds like I understood you correctly.
>
>> Is there a way to "grow" the existing UBI device so that it now also
>> covers the rest of the NAND chip?  Or is my only option to create a
>> second UBI device?
>
> I think so, unless you use the fastmap feature. Suppose you don't.
>
> There are 2 parts - UBI and UBIFS.
>
> So, let's suppose your situation is like this.
>
> 1. You have 2 mtd partitions - mtd1 and mtd2.
> 2. mtd1 has JFFS2 with important files.
> 3. mtd2 is the extra partition you have.
>
> I guess you can do this.
>
> 1. Format mtd2 with UBI. Just erasing should be OK, or you can use
> ubiformat: http://www.linux-mtd.infradead.org/faq/ubi.html#L_ubierase
>
> Then you attach mtd2 (ubiattach) and you get an UBI device (/dev/ubiX).
>
> 2. Create a volume on /dev/ubiX which spans entire UBI device
> (ubimkvol -t AFAIR). You end up with UBI volume /dev/ubiX_0.
>
> 3. And here is important part - you format /dev/ubiX_0 with JFFS2 but
> correctly.

s/JFFS2/UBIFS :-)

> UBIFS has this "automatic expand" feature. Which means that if the UBI
> volume underneath it becomes larger, UBIFS will expand automatically and
> take the entire (larger) UBI volume.
>
> However, there is a _limit_ to how much UBIFS can expand from the
> original size. And you want to watch this limit and make it big enough.
>
> The limit is connected with the "-c" option of mkfs.ubifs. Please, check
> the docs - they explain what exactly -c controls and how it is related
> to the maximum UBIFS file-system size:
>
> http://www.linux-mtd.infradead.org/faq/ubifs.html#L_max_leb_cnt
>
> So, select proper -c.
>
> If you do not use mkfs.ubifs, but just attach /dev/ubiX_0, the UBIFS
> kernel driver will format the volume automatically. It will select the
> -c value itself. Since this value is power of 2, it will just take the
> smallest power-of-2 value. It may be OK for your purposes, may be not.
> It is safer to use mkfs.ubifs with explicit -c.
>
> Basically this is the trickiest part, rest _should_ be easy, but you'll
> learn when you try :-)
>
> 4. Copy important files from JFFS2-mtd1 to UBIFS-UBI-mtd2.
>
> 5. Erase mtd1 (or you can do this later too)
>
> 6. I do not know how you do this, but kill mtd1, and resize mtd2.
> Probably mtd2 will then be named mtd1 after reboot. If you always refer
> your MTD partitions and UBI volumes by name, you should not suffer to
> much from mtd2 becoming mtd1.
>
> Lets suppose there is no rename, for simplicity.
>
> 7. Make sure former JFFS2-mtd1 eraseblocks are erased (unless you did
> this at step 5).
>
> 8. Attach mtd2 to UBI. UBI will automatically "take" the new
> eraseblocks, erase them and write UBI headers there, and make available.
>
> 9. Volume size will still be the same, and you need to re-size it using
> ubiresize.
>
> 10. Mount the resized volume. UBI will enlarge itself.
>
> Problem solved.
>
> Surely you do not want power cuts during this operations. If you need to
> survive power cuts, I guess it is possible, but more complex.
>
> HTH.
>
> --
> Best Regards,
> Artem Bityutskiy
>
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/



-- 
Thanks,
//richard