[dm-devel] Re: Help tracking down problem --- endless loop in __find_get_block_slow

[Andrew Morton]

zensonic at zensonic.dk (Thomas S. Iversen) wrote:
>
> > OK, so we're looking for the buffer_head for block 101 and the first
> > buffer_head which is attached to the page represents block 100.  So the
> > next buffer_head _should_ represent block 101.  Please print it out:
> 
> Not quite the same, but simelar:
> 
> Feb 23 14:50:24 localhost kernel: __find_get_block_slow() failed. block=102,
> b_blocknr=128, next=129
> Feb 23 14:50:24 localhost kernel: b_state=0x00000013, b_size=2048
> Feb 23 14:50:24 localhost kernel: device blocksize: 2048
> Feb 23 14:50:24 localhost kernel: ------------[ cut here ]------------

Something has caused the page at offset 51 (block 102) to have buffer_heads
for blocks 128 and 129 attached to it.

> > Could be UFS.  But what does "transparent block encryption and sector
> > shuffling" mean?  How is the sector shuffling implemented?
> 
> GDBE is a block level encrypter. It encrypts the actual sectors
> transparently via the GEOM API (corresponds to the devicemapper api in linux).
> 
> GBDE assigns a key for each block, thereby introducing keysectors.
> Furthermore the sectors are remapped so that one can not guess where e.g.
> metadata is located on the physical disk. It is a rather simple remap:

I'd be suspecting that the sector remapping is the cause of the problem. 
How is it implemented?