Implement size and write_back for block SOs
Implement size and write_back for block SOs

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

mikenawrocki/rtslib-fb,mikenawrocki/rtslib-fb,cvubrugier/rtslib-fb,agrover/rtslib-fb