[dm-devel] [Question] Changes to dm do not reflect in underlying block device

[Jasper Surmont]

I created my own dm which performs some checks on writing / reading
before it remaps the request to an underlying block dev. After I set
it up and write changes (eg using 'dd') to /dev/mapper/<name>, I see
it happened correctly (eg using 'hd' on /dev/mapper/<name>). However,
the underlying block device did not change at all (again using 'hd' on
/dev/sdb1 for example).
1. How is it possible that, even though the changes are not yet
persisted to /dev/sdb1, the dm has the correct data?
2. Is this normal behavior? If not, what can I do or what am I doing
wrong to fix this?

Thanks!

Cheers, Jasper