I wrote a basic device mapper driver which caches reads.
I gave dm msg prefix as below
#define DM_MSG_PREFIX "cacheread".
When i try to create a device mapper node using the below command
echo "0 `blockdev --getsize /dev/sda2` cacheread /dev/sda2 0" | dmsetup create cacheread
the system hangs.I am not getting any error messages.