> >
> > > 1. what does function yaffs2_scan_backwards do?
> >
> > This function scans the nand partition if there is no checkpoint. It
> > reads the
> > tags and builds up the file system state.
> >
> > > 2. MTD keeps a BBT (in NAND in my case), how does yaffs2 module
> >
> > obtains
> >
> > > the BBT information? Why rescan from backward is needed in my case
> > > in order to recover a file system.
> >
> > Yaffs calls the MTD function to determine if a block is good or bad.
> > Yaffs does not know or care if mtd used a bad block table or not.
> >
> > > 3. After recovering the system, seems the bad block information is
> > > not saved. So re-scan is still needed after a reboot. This is my guess,
> > > please correct me if I am wrong.
> > >
> > > Also I am using a quite old version of yaffs2 ( back in 2010). What's
> > > the most recommended stable version of yaffs2,
> >
> > I suggest using a more recent version. I would recommend using the
> > current HEAD.
> >
> > > and the kernel MTD driver
> > > version?
> >
> > Sorry I don't keep current with all mtd changes and cant't advise that
> > off the
> > top of my head.
> >
> > > To cut some boot up time I am saving BBT on NAND and reuse it
> > > after reboot, will this make any negative impact?
> >
> > I don't see that this will cause any problems. yaffs does not care how or
> > if
> > you store bbt info.
> >
> > > I am interested in block
> > > summaries, but I would like to stick to checkpoint at the moment.
> >
> > If you use the new code you will get summaries as part of the
> > improvement.
> >
> > > I am new to kernel level debugging, so I am quite lost here. Any help
> > > is appreciated. Thanks!
> >
> > We've all been there.
> >
> > > regards,
> > > Peter
> > >
> > > On Mon, Apr 30, 2012 at 7:41 AM, Charles Manning
> >
> > <
manningc2@actrix.gen.nz>wrote:
> > > > On Saturday 28 April 2012 05:26:23 Peter Lin wrote:
> > > > > I have several NANDs that yaffs2 module would consider itself
> > > >
> > > > successfully
> > > >
> > > > > recovered from check pointing and skip scanning, but the filesystem
> >
> > is
> >
> > > > not
> > > >
> > > > > usable. Mounting with option no-checkpoint-read could recover the
> > > > > filesystem.
> > > > >
> > > > > I understand that bad block management shall be provided from MTD
> > > > > layer, and rescanning fixing the problem proved MTD is doing his
> > > > > job. But I do have some questions:
> > > > >
> > > > > 1. why in the first place the check point restoring succeeded but
> >
> > left
> >
> > > > > a corrupted filesystem?
> > > >
> > > > It is impossible to say with so little info.
> > > >
> > > > > 2. What would happen if a used block become a bad
> > > > > block?
> > > >
> > > > That block will not be scanned. But blocks don't just"go bad". We
> > > > have
> >
> > to
> >
> > > > mark
> > > > them as bad, That normally means we have timne to extract the useful
> >
> > data
> >
> > > > first.
> > > >
> > > > > will the whole filesystem got crazy?
> > > >
> > > > No. Yaffs uses a log structure with tags. That means there is no
> >
> > "master
> >
> > > > table" or such which holds all the information.
> > > >
> > > > > Any way to recover from it?
> > > > >
> > > > > 3.
> > > > > Any way to check or indicate an inconsistence in the filesystem, so
> >
> > the
> >
> > > > > mounting script could try with the option no-checkpoint-read?
> > > >
> > > > There is no such provision at present. Since there is no scanning if
> >
> > the
> >
> > > > checkpoint works, it is really hard to see how you would decise that
> >
> > the
> >
> > > > checkpoint was bad.
> > > >
> > > > If you are having problems with checkpoint, then consider just
> > > > turning
> >
> > it
> >
> > > > off.
> > > > Since block summaries were introduced, the boot speed up benefits of
> > > > checkpointing are not as dramatic as they were.
> > > >
> > > > > Thanks for your work and help. Please let me know if there's any
> > > > > mistake
> > > >
> > > > in
> > > >
> > > > > my understanding.
> > > > >
> > > > > regards,
> > > > > Peter
> > > > >
> > > > > does the official kernel has this function enabled or is there any
> > > > > option that controls it?
> > > > >
> > > > > On 2010-03-04 20:55, Charles Manning wrote:
> > > > > > On Friday 05 March 2010 07:14:59 Shivdas Gujare wrote:
> > > > > > > Hi Charles,
> > > > > > >
> > > > > > > Thanks lot for your help.
> > > > > > >
> > > > > > > On Wed, Mar 3, 2010 at 12:34 PM, Charles Manning
> > > > > > >
> > > > > > > wrote:
> > > > > > > > On Wednesday 03 March 2010 23:33:31 Sven Van Asbroeck wrote:
> > > > > > > >> Hello Shivdas,
> > > > > > > >>
> > > > > > > >> > So, what does actually "check pointing" saves while
> > > > > > > >> > unmount?
> > > > > > > >>
> > > > > > > >> It's my understanding that the check point consists of the
> > > > > > > >> RAM
> > > >
> > > > data
> > > >
> > > > > > > >> structure which is assembled when a yaffs partition is
> >
> > scanned.
> >
> > > > > > > >> It consists of meta-information associated with each chunk
> > > > > > > >> and block. If you'd like to know more, I recommend reading
> > > > > > > >> the
> >
> > 'How
> >
> > > > > > > >> Yaffs works' document, which is available in CVS.
> > > > > > > >
> > > > > > > > A full scan builds up a set of data structures that define
> > > > > > > > the file system state. A checkpoint captures a reduced
> > > > > > > > version of that,
> > > >
> > > > enough
> > > >
> > > > > > > > to reconstitute the main part of the state and the rest can
> > > > > > > > be
> > > >
> > > > built
> > > >
> > > > > > > > up on a lazy basis.
> > > > > > > >
> > > > > > > >> > and Is it
> > > > > > > >> > safe to use check-pointing always in final product?
> > > > > > > >>
> > > > > > > >> According to Charles, checkpointing is designed to be used
> > > > > > > >> in the way you describe. To my knowledge, no open
> > > > > > > >> checkpointing issues exist, but you should search the
> > > > > > > >> archives. If you are concerned about the checkpoint
> > > > > > > >> diverging from the
> > > > > > > >> meta-information on flash, you could a) disable
> > > > > > > >> checkpointing altogether, or b) submit a
> > > >
> > > > patch
> > > >
> > > > > > > >> implementing a checkpoint counter ;-)
> > > > > > > >
> > > > > > > > You can also choose to mount ignoring checkpointing with
> > > > > > > >
> > > > > > > > mount -t yaffs2 -o"no-checkpoint-read" ..
> > > > > > >
> > > > > > > This is not the option for me, since in final product, end user
> > > >
> > > > should
> > > >
> > > > > > > not be able
> > > > > > > to change system data (i.e. mount flag's.) Or I can't change it
> > > >
> > > > unless
> > > >
> > > > > > > rootfs is flashed
> > > > > > > on device, since yaffs2/nand partitions are mounted from rcS
> > > > > > > script.
> > > > > >
> > > > > > You don't need to do this. Just leave checkpointing on.
> > > > > >
> > > > > > -- CHarles
> > > > > >
> > > > > >
> > > > > > -- Charles
> > > > >
> > > > > -Peter
> > > > > _______________________________________________
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