Re: validate_sb: bad superblock, error 8 (Minimum UBI volume size for UBIFS image)

[Artem Bityutskiy <dedekind1@gmail.com>]

On Sat, 2011-01-15 at 22:09 +0000, Andrew Murray wrote:
> On 15 January 2011 10:48, Andrew Murray <amurray@mpcdata.com> wrote:
> > On 11 January 2011 09:47, Andrew Murray <amurray@mpcdata.com> wrote:
> >>
> >> Is there a way to determine the minimum UBI volume size which will
> >> support a given UBIFS filesystem image?
> >>
> >
> > My conclusion is this (with my version of kernel and mkfs.ubifs tool):
> >
> > (Min No. UBI Volume LEBS) = (jrn_lebs) + 3 + (log lebs) + (lpt_lebs) +
> > (orph_lebs)
> >
> > And these values can all be determined (or specified) by the
> > mkfs.ubifs tool by using the verbose -v flag.
> >
> > This seems to hold true - Does this seem reasonable?
> 
> After reading the ODP presentation, white paper and reading the source
> - I do not understand the purpose of the second condition in the
> following test case in validate_sb:
> 
>         if (c->max_bud_bytes < (long long)c->leb_size * UBIFS_MIN_BUD_LEBS ||
>             c->max_bud_bytes > (long long)c->leb_size * c->main_lebs
> 
> It seems to be asserting that there is enough space on the volume to
> cater for the maximum size of the journal. However in the case where
> the UBI volume is similar in size to the UBIFS image data -
> 'main_lebs' will mostly be absent of free space lebs. Therefore there
> may not be enough room for max_bud_bytes amounts of journal. And in
> any case the journal code seems to cater well for there not being
> enough free lebs. (Presumably it copes when the volume is nearly
> full).
> 
> Therefore is this condition superfluous?

Hi, I'm not able to give you any reasonable answer right now (vacation,
and already have long backlog of e-mails to answer), sorry for this. But
the space calculations may have issues - we did not work on that well
enough, and did not test them with different journal sizes, etc. Just
did not spend much time on those things - wrote the code which
calculates some default sizes and used that all the time. AFSIK,
mkfs.ubifs is mostly copy-paste of the kernel code, including the
default geometry calculations.

Please, feel free to send patches.

-- 
Best Regards,
Artem Bityutskiy (Битюцкий Артём)