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Subject: Re: ubi_eba_init_scan: cannot reserve enough PEBs
From: Stefani Seibold <stefani@seibold.net>
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Date: Thu, 02 Sep 2010 08:47:13 +0200
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Am Mittwoch, den 01.09.2010, 18:47 +0300 schrieb Artem Bityutskiy:
> Hi,
> 
> On Tue, 2010-08-31 at 14:09 +0200, Stefani Seibold wrote:
> > Am Sonntag, den 22.08.2010, 18:04 +0300 schrieb Artem Bityutskiy:
> > > 
> > > Yes, but your patch fixes the symptom, unfortunately. It is ok for you
> > > to use as a work-around, but I still hope to find the root cause.
> 
> > True, but also if we fix the cause, this could happen. Imagine that one
> > of the two master LEB will get corrupted, due a flash error or a power
> > fail during a write access. Than the system should able to mount this
> > damaged file system and restore the lost master LEB.
> 
> Firs of all, UBIFS _does_ handle the situation when on master LEB is
> corrupted. It is designed for this and this part was tested. _But_ UBIFS
> expects that the master LEB is corrupted in _certain way_. If it is
> corrupted in an unexpected way - we panic.
> 
> To put it differently, we do not handle random corruptions, we handle
> only corruptions which _look_ like corruptions caused by power cuts.
> 

That is the point! Panic or refuse to mount is not a good solution. If
there is a way to mount the file system, than do it. Maybe read-only
with a big fat warning, but this is better than nothing. This is like
the ext3 fs, which handles this also in this way.

> In your case you have very strange corruption. We can apply your patch,
> problem solved, but will you be 100% comfortable with this? There is a
> chance that you have some issues which can later have different
> symptoms. I am still interested to find out the real root reason.
> 

No a will be not 100% comfortable with this, but it is better than
nothing. I agree with you to fix the cause and not the symptoms, but may
patch will help to get your data back in case of this bug.
 
Greetings,
Stefani