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.net or
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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