linux-kernel - Re: UBI fastmap updates

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Message-ID: <20120802190617.7182924f@spider.haslach.nod.at>
Date:	Thu, 2 Aug 2012 19:06:17 +0200
From:	Richard Weinberger <richard@....at>
To:	Tim Bird <tim.bird@...sony.com>
Cc:	"artem.bityutskiy@...ux.intel.com" <artem.bityutskiy@...ux.intel.com>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"adrian.hunter@...el.com" <adrian.hunter@...el.com>,
	"Heinz.Egger@...utronix.de" <Heinz.Egger@...utronix.de>,
	"thomas.wucher@...utronix.de" <thomas.wucher@...utronix.de>,
	"shmulik.ladkani@...il.com" <shmulik.ladkani@...il.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"Marius.Mazarel@...l.ro" <Marius.Mazarel@...l.ro>,
	"nyoushchenko@...sta.com" <nyoushchenko@...sta.com>
Subject: Re: UBI fastmap updates

Am Thu, 2 Aug 2012 10:03:04 -0700
schrieb Tim Bird <tim.bird@...sony.com>:
> >> If everything goes wrong, fastmap makes sure that no fastmap is on
> >> flash.
> >> In case of a powercut we fall back to scanning mode.
> >> R/O mode is overkill IMHO.
> > 
> > So can I interpret this the following way. Not only fastmap give no
> > guarantees that it exists after an unclean reboot, it does not even
> > give guarantees that it exists after a clean reboot.
> > 
> > Unless I am confused, the fastmap design is over-simplified.
> 
> Fastmap is an optimization.  Maybe I'm missing something, but
> I'm not sure why, if the optimization stopped working, you
> would want to reduce the functionality of the file system.

That's *exactly* my point.
If fastmap is available - fine, we have fast boot - yay!
But if something really nasty happens we can safely fall back
to scanning mode.
And fastmap is designed to allow this.

Thanks,
//richard
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