[Yaffs] Re: Why does YAFFS skip the first block?

[Wookey]

+++ Peter Barada [05-06-22 02:27 -0400]:
> > The mkyaffsimage output is fine, so long as you write it into flash starting 
> > at startBlock.
> 
> Yeah, I figured that out, finally.  You can imagine if you loaded the
> YAFFS image at block zero, and ignored the first 256K of data from the
> image, some *really* wierd stuff happens including root directory
> objects that never show up, and a lost+found that contains objects that
> have no contents(due to missing objects located in the first 256K).

> > > Only after its taken a long day of yanking your hair out to understand
> > > the problem.  No offense, but yaffs_fs.c, yaffs_mdtif.c and
> > > mkyaffsimage.c don't match as they exist now, and the documentation
> > > doesn't mention that the image created by mkyaffsimage.c should be
> > > offset by a flash block so that it all works.  Anyone who's marched down
> > > this path should be able to tell you that.
> > 
> > 
> > The mkyaffsimage output is completely location independent, but it is 
> > expected to be used with mkyaffs (which loads starting at block one). If you 
> > take the image and load it into flash at block 1 you'll be OK.
> 
> I understand that mkyaffsimage produces a location independent image,
> but it *does* matter where it it is placed such that YAFFS actually
> accesses all of it.
> 
> > In what way don't they match? 
> > 
> > AFAIK,
> > 1) yaffs_fs.c uses startBlock of 1
> > 2) mkyaffs loads from block 1
> > 3) yaffs_guts says block zero is not permitted.
> 
> I have a separate bootloader that knows how to erase/burn flash.  I'm
> trying to use YAFFS as a *root* filesystem, so it has to be burned from
> a boot-loader, and not from Linux, so mkyaffs doesn't help me here.  I'd
> figure if mkyaffsimage is like mkfs.jffs2, it produces an image that can
> be burned *directly* into flash without the need for a support program
> (such as mkyaffs).  And if YAFFS is my root FS, then I have a catch-22
> here if I require mkyaffs...
> 
> Documentation/yaffs-rootfs-howto.html has:
> 
> <H3>Creating a bootable yaffs partition:</H3>
> <P>You can</P>
> <P>1) Create the partition by mounting it from a running linux os and
> copying the data there. The mkyaffs utility in the yaffs source
> simply erases a NAND mtdblock device without removing bad block
> data.</P>
> <P>2) Make and download a filesystem image. The mkyaffsimage utility
> that came with the sources will create a YAFFS block list in a file
> from a root tree. This is a list of 512+16 byte blocks that need to
> be placed (in any order) on a NAND device.</P>
> <P>You will need to write code to copy these data blocks and add in
> the block numbers in the oob areas.</P>
> 
> Nowhere does that mention that mkyaffs is *required* to load the image
> created by mkyaffsimage into the NAND device so that it 'shuffles' the
> image past the first block.  It describes mkyaffs as 'simply erases a
> NAND mtdblock device'.  That can be accomplished by most boot-loaders.

Point taken. Thanx for pointing out that this isn't clear. We are working on
better/newer docs now so this should get fixed fairly soon.

Wookey
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