format: add support for dev_fill() and extra dev_*() debugging.

Support an fs_io dev_fill().
This helps with devices that actually already return 0 on uninitialized
data. It also helps with in memory devices using sparse libs: don't
allocate a block of 0s.

Signed-off-by: JP Abgrall <jpa@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
3 files changed