UBI fastmap updates

[Artem Bityutskiy]

On Thu, 2012-08-02 at 16:51 +0200, Richard Weinberger wrote:
> Every time fastmap writes a new fastmap to the flash it tries to get a
> new PEB and returns the old one (used for the old fastmap) back to the
> WL sub-system.

OK.

> If no free PEBs are available (E.g Volume is full or the erase worker
> is too slow) ubi_wl_get_fm_peb() returns NULL and fastmap reuses the
> currently used PEB.

This should not happen. Fastmap should _reserve_ enough of PEBs for it
to operate. It should always find the PEB to write.

Just like if you create a volume maximum possible size, we guarantee
that you can fill it with data, and UBI will find enough PEBs for that.

Just like we always have enough PEBs for the volume table.

The above things are UBI's liabilities.

In the situation when a lot of PEBs became bad, UBI will switch to R/O
mode with a scary message if it notices that it does not have enough
PEBs to satisfy all the liabilities.

And this is why we reserve 2% of PEBs for bad PEBs handling.

> In this situation ubi_wl_get_fm_peb() may trigger such an error message.
> If think we should get rid of the message as this is not an error
> condition. It's a well known execution path.

Unless I am confused, this should lead to switching to R/O mode instead,
just like we do when we write to an LEB and do not find a PEB to map to.

-- 
Best Regards,
Artem Bityutskiy
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