Grow UBI device?

[Wolfgang Denk]

Dear Ricard Wanderlof,

In message <alpine.DEB.2.00.1310091038110.28562 at lnxricardw.se.axis.com> you wrote:
> 
> > 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?
> 
> UBI devices are 'attached' to existing mtd partitions. So to grow a UBI 
> device, you need to detach it from the partition, re-partition the flash 
> (and I'm not sure if this step is even possible as it involves 
> unregistering existing mtd partitions), then attach a UBI device to the a 
> new partition.

In my situation it is OK if the update involves a reboot, so it is
certainly possible to change the MTD partition layout.  So this should
not be a problem.

> Come to think of it, I'm not sure that would work anyway, as the 
> resulting, new, enlarged partition would partly contain UBI data and 
> partly old jffs2 data. I'm not sure what UBI does when it encounters 
> incorrect data, if it just erases the relevant blocks and formats them for 
> its own use, or if it barfs completely and just bails out complaining that 
> the partition does not contain UBI data. If the relevant blocks were 
> erased, then I think UBI would simply concede that the a previous erase 
> attempt had been prematurely aborted, and re-erase the blocks and write 
> its headers, so perhaps that is something to try. At any rate it involves 
> at least some mild trickery (erase the blocks that previously contained 
> jffs2 data).

well, this is the exact part where I wanted to know if (1) this is
guaranteed to work (by design), and/or (2) somebody has successfully
done it before.

> It's probably easier to create a new UBI device by attaching it to the 
> partition previously used by jffs2, after erasing it, but multiple UBI 
> devices across a flash partly defeats the purpose of wear-leveling which 
> UBI provides.

Right, and it fragments the device.  That's why I'd like to avoid
that.


Thanks!!

Best regards,

Wolfgang Denk

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