linux-kernel - Re: [PATCH 5/5] ubi: Allow to use read-only UBI volume with not enough PEBs

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Date:   Tue, 25 Jul 2017 16:27:29 +0200
From:   Pali Rohár <pali.rohar@...il.com>
To:     Richard Weinberger <richard.weinberger@...il.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Artem Bityutskiy <dedekind1@...il.com>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] ubi: Allow to use read-only UBI volume with not
 enough PEBs

On Friday 21 July 2017 22:12:51 Richard Weinberger wrote:
> Pali,
> 
> On Fri, Jun 2, 2017 at 5:43 PM, Pali Rohár <pali.rohar@...il.com> wrote:
> > In read-only mode is skipped auto-resize. For pre-build images ready for
> > auto-resize there can be reserved more PEBs as whole size of pre-build
> > image. In read-only we do not do any write operation therefore this would
> > allow to use read-only UBI volume which is not auto-resized yet.
> >
> > Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> > ---
> >  drivers/mtd/ubi/vtbl.c |   14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/mtd/ubi/vtbl.c b/drivers/mtd/ubi/vtbl.c
> > index 263743e..1d708c5 100644
> > --- a/drivers/mtd/ubi/vtbl.c
> > +++ b/drivers/mtd/ubi/vtbl.c
> > @@ -240,8 +240,10 @@ static int vtbl_check(const struct ubi_device *ubi,
> >                 if (reserved_pebs > ubi->good_peb_count) {
> >                         ubi_err(ubi, "too large reserved_pebs %d, good PEBs %d",
> >                                 reserved_pebs, ubi->good_peb_count);
> > -                       err = 9;
> > -                       goto bad;
> > +                       if (!ubi->ro_mode) {
> > +                               err = 9;
> > +                               goto bad;
> > +                       }
> 
> I fear this is not correct, it will disable a legit self-check of UBI volumes.
> If the read-only volume is corrupted/truncated and you miss PEBs, this
> check will no longer
> trigger.
> 
> Especially when dealing with nanddumps, truncation is a common problem.

Any idea how to fix it? Or how to handle read-only images which are
marked for auto-resize?

-- 
Pali Rohár
pali.rohar@...il.com