After spending sometime looking around in my corrupted NAND, I think I am
clear what's going on there:
There's some *outdated* checkpoint block in the bad blocks portion, and the
real good one is located at a later block. During mounting, yaffs firstly
found the *outdate* checkpoint block and loaded from there. That's why
loading from checkpoint will always result a corrupted FS, even after
re-scanning all the blocks with no-checkpoing-read.
now the question part:
1. why in the first place there's some checkpoint block 'left over' in
the bad blocks? shall they be erased?
2. While looking for a checkpoint block, shall the block status be
checked? Or is there any better way to handle this situation? I simply used
mtd->block_isbad and continue searching and it seemed working.
regards,
Peter
On Mon, May 7, 2012 at 3:08 AM, Charles Manning <
manningc2@actrix.gen.nz>wrote:
> On Friday 04 May 2012 00:30:55 peterlingoal wrote:
> > Hi Charles,
> >
> > Thanks for the reply.
> >
> > I am quite confused about the bad block management methodology, seems
> both
> > MTD and yaffs2 have some kind of bad block control. The problem of my
> case
> > is, after some period of usage, the yaffs2 file system on some NAND begin
> > to fail. Remounting with ignoring checkpoint could recover the file
> system,
> > but for once only. The file system is still boomed after reboot and mount
> > (with checkpoint).
> >
> > I tried to read the codes of yaffs2 about scanning if checkpoint is
> > ignored, and got confused. Seems yaffs2 driver is querying status of each
> > block (in function yaffs2_scan_backwards). My question is:
>
> I suggest you read the HowYaffsWords doc. You can find that on yaffs.netor
> find the openoffice doc on the yaffs git.
>
> > 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
> > > > _______________________________________________
> > > > yaffs mailing list
> > > > yaffs@lists.aleph1.co.uk
> > > > http://lists.aleph1.co.uk/cgi-bin/mailman/listinfo/yaffs
>
>
>
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