Re: padding in mkfs.jffs2 and nandwrite

[Johannes Stezenbach <js@linuxtv.org>]

On Wed, Dec 14, 2005, Johannes Stezenbach wrote:
> I've prepared a jffs2 image with mkfs.jffs2 and written it to
> NAND flash using nandwrite (details below). When the file system
> is mounted r/w and written to, on future mounts the following
> warning appears:
> 
> 	Empty flash at 0x000000f8 ends at 0x00000200
> 
> This is caused by the padding added by either mkfs.jffs2 -p512
> or nandwrite -p, because this padding is 0xff, which jffs2
> sees as "free space which was wasted" (when jffs2 flushes
> a page to disk it pads with 0x00, so it can tell that this space
> was deliberately left unused).
> (I think this warning will evetually go away when the block is garbage
> collected, but this can take a loooong time.)
> 
> To avoid this warning I would like to suggest that we either
> change mkfs.jffs2 and nandwrite to pad with 0x00, or add
> an option to both to choose the padding value.
> 
> One additional question: Why does mkfs.jffs2 -p by default
> pad to the end of the erase block? When whole pages are written
> with all 0xff, but the first N pages of an erase block contain
> valid nodes, jffs2 will assume that these pages are freshly
> erased and good to write in.
> Won't this cause instable bits when written again by jffs2?
> (The data sheet for my flash says that there may be up to
> three partial page write before erase is needed, but I'm not sure
> if this allows to write the same byte twice.)
> 
> What I currently do to avoid the issue:
> 
> $ mkfs.jffs2 -v -e16384 -d foo -b -n -q | dd bs=512 conv=sync >foo.jffs2
> $ flash_eraseall -j /dev/mtd0
> $ nandwrite /dev/mtd0 foo.jffs2

Would someone be so kind and comment on this?

Why is padding handled differently in fs/jffs2/ and mkfs.jffs2?
Is it a bug?

Greetings,
Johannes