linux-kernel - Re: [RFC v2] UBI: UBIVIS (aka checkpointing) support

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Message-ID: <1336733182.2625.17.camel@sauron.fi.intel.com>
Date:	Fri, 11 May 2012 13:46:22 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	linux-mtd@...ts.infradead.org, tim.bird@...sony.com,
	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	Heinz.Egger@...utronix.de
Subject: Re: [RFC v2] UBI: UBIVIS (aka checkpointing) support

On Thu, 2012-05-10 at 10:33 +0200, Richard Weinberger wrote:
> First of all, yes it's fully backward-compatible. It uses two new internal volume IDs
> with compat = UBI_COMPAT_DELETE.
> Old UBI implementations will delete the checkpoint and continue with scanning...

OK. BTW, these patches do not compile when the fastmap is disabled. I
hope you'll just kill the ifdefs in the next revision and this problem
will go away.

> Regarding design, ubi_wl_get_peb() currently offers three types of data types.
> UBI_LONGTERM, UBI_SHORTTERM and UBI_UNKNOWN. Do we really need them?
> Checkpointing has a pool of unknown PEBs. This PEBs have to be scanned while attaching.
> For now I had to create three pools (for UBI_LONGTERM, UBI_SHORTTERM and UBI_UNKNOWN).
> This makes the whole thing complexer than needed.
> It introduces also some nasty corner cases.

But AFAIR we already agreed that we kill these, no? I thought you'll
send a separate patch for this. We do not need this feature and to our
shame it even was not working and there was a bug found very recently.

> To make the review easier for you:
> The most critical code path is scan_pool() -> process_pool_seb() -> update_vol().
> It searches within a pool for PEBs which are no longer empty and scans them.
> After that it updates the corresponding volume.

OK, thanks.

> ubi_update_checkpoint() is also very important because it has to find
> unused PEBs at the beginning of the MTD to place the super block.

OK.

> Okay, got your point.
> I think "fastmap" is a good name because I can also use it within the code.
> So, while reviewing the code please keep s/checkpoint/fastmap/g and s/cp/fm/g in mind. ;-)

OK.

-- 
Best Regards,
Artem Bityutskiy

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