Re: [PATCH 0/5] Add flight recorder to MTDRAM

[Richard Weinberger <richard@nod.at>]

Manfred,

Am Mittwoch, 6. Dezember 2017, 20:44:55 CET schrieb Manfred Spraul:
> Hi Richard,
> 
> On 12/06/2017 11:41 AM, Richard Weinberger wrote:
> > Dirk, Manfred,
> > 
> > Am Mittwoch, 6. Dezember 2017, 09:50:34 CET schrieb Dirk Behme:
> >> From: Manfred Spraul <manfred@colorfullife.com>
> >> 
> >> Hi,
> >> 
> >> The series adds a flight recorder to MTDRAM.
> > 
> > Thanks a lot for sharing your tool, this is highly appreciated.
> > 
> >> This allows very efficient power fail testing:
> >>  From the flight recorder output, it is possible to recreate every image
> >> 
> >> that might have existed between the start of the recording and the end.
> >> 
> >> Obviously, a user space tool is required, it is attached as the last
> >> mail in the series.
> > 
> > So, to understand this approach better I need to recap.
> > The "flight recorder" logs every single MTD operation (READ, ERASE,
> > PROGRAM) to a file while the MTD is under load, right?
> 
> Only ERASE and PROGRAM. READ is not logged.
> Would it help if READ is logged as well? (memory is cheap, ...)
> 
> What would be fairly simple is to add a backtrace for every ERASE and
> PROGRAM. I'll try to add that.

Given a second thought, for power-cut testing READ is not important.
So no need to hurry.

> > Then you take the log, replay it to a _file_ but instead of replaying
> > all N MTD operations only N - X operations are replayed?
> 
> Exactly.  Instead of replaying all N operations, only X operations are
> replayed.
> 
> image-168167.bin is after replaying 168167 operations.
> image-168168.bin is after replaying one additional operation.

This is what I thought.
It worries me a bit that image-168167.bin shows a corrupted LPT (LEB property 
tree). The current logical operation of UBIFS is writing the index tree.

> > The output file is later written back to MTDRAM to check how much UBIFS
> > likes it?
> 
> Exactly.
> 
> > While having such a tool would be awesome, we have to be very sure that it
> > behaves correctly.
> > Yesterday I spent almost the whole night with staring at some of Manfred's
> > images and I'm not sure whether what I see makes sense or can actually
> > happen on a real NAND or NOR flash. But I'm still investigating.
> 
>  From my understand, the tool result is exactly identical to a powerfail
> immediately after PROGRAM.

Yes.

> What differs from realistic embedded systems is obviously performance:
> RAM disk+2-core I3 is probably much faster & much more parallelism happens.

Yep. I found also some UBI and UBIFS on my x86 system with nandsim and 
powercuts over the last years.

> I have uploaded the initial image, the final image and the flight recording.
> 
> https://sourceforge.net/projects/calculix-rpm/files/ubifs/xattr/

Cool! I'll give it a try.

Thanks,
//richard