Request for comments: UBI PEBs as a multiple of erase size

[Atlant Schmidt]

Kevin:

  I would support this change.

  Today, do we allow "mixed" NAND Flash device with the
  possibility of multiple Erase Block sizes? It seems to
  me that your patch, fully-fleshed-out, would allow this
  and that also seems like a good thing.

                                Atlant

-----Original Message-----
From: linux-mtd-bounces at lists.infradead.org [mailto:linux-mtd-bounces at lists.infradead.org] On Behalf Of Kevin Paul Herbert
Sent: Tuesday, September 13, 2011 15:37
To: linux-mtd at lists.infradead.org
Subject: Request for comments: UBI PEBs as a multiple of erase size

I came across a situation where I wanted to be able to use the same pre-built (with UBI) image on two different FLASH devices, one of which having a larger erase size than the other. I actually did not notice that the device I was using had a different erase size, which caused UBI to quietly corrupt my FLASH.

I have a patch to UBI (kernel and ubinize) to store the size of a PEB in the EC header, reject attaching if the PEB size is not equal to or an integer multiple of the erase size, and treat multiple erase blocks as a "cluster" for I/O operations.

I looked through a few months of archives to see if this is a common problem, and I don't see this as being discussed. Is there interest in me publishing this patch for inclusion in the kernel. The only downside I can see of my change is that it adds an additional 32 bit quantity to struct ubi_ec_hdr, reducing the available free header byets from 35 to 31. For backwards compatibility, if this field is zero, I treat it as PEB size == erase size.

It seems to me that having the PEB size in the header, regardless of supporting multiple erase blocks as a single PEB, is a useful consistency check.

Comments please?

Thanks,
Kevin Paul Herbert
Meraki, Inc.


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