linux-kernel - Re: [PATCH] UBIFS: compute KSA size and store in superblock

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Date:	Sat, 26 May 2012 13:21:38 +0200 (CEST)
From:	Joel Reardon <joel@...mbassador.com>
To:	Artem Bityutskiy <dedekind1@...il.com>
cc:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] UBIFS: compute KSA size and store in superblock

>
> I do not have to time to review it now, but please, make sure that the
> KSA size is according to 'max_leb_cnt' (see the --max-leb-cnt of the
> mkfs.ubifs tool).

Ahh, I see now I also need to add the min number of lebs to min_leb_cnt if
the feature is enabled.

> Also, think about this use-case in general: you have
> UBI volume of size X, then the volume is resized to Y > X, then mounted
> - UBIFS should work and resize itself to Y, up to the 'max_leb_cnt'. If
> Y > 'max_leb_cnt', we resize only to 'max_leb_cnt'.

For this case, it should be fine if the KSA is sized to maxlebcnt.
However, it will remain that size regardless of the real leb_cnt.

In general, removing KSA blocks is possible, but if datanodes are
encrypted with keys on those blocks, then they must be re-encrypted with a
different key on the smaller set (or somehow write the new last KSA block
containing all the used keys from the removed KSA blocks along with a
relocation table, but this seems like alot of coding if removing LEBs from
the KSA isn't that important.)

Adding LEBs to the KSA is very simple, just add a new entry on the list
and set all the key states to deleted--after purging will be random data;
but KSA LEBs are logically-sequential, so if it comes from used main LEBs
the data nodes need to be relocated. or some complicated code structure
involved in determining where a key for an out-of-range KSA block is
remapped.

Cheers,
Joel Reardon
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