split_bio_demo init
Do not submit our bio
...
schedule before submit...XXX
add srl struct
add init_srl
add meta info in split_bio_list
...
...
... local syncer,
implement syncer. write data from srl to disk.[can work]
init buffer...
...
buffer: add a inuse_list
write bio: add srl_data in the bio_struct
implement buffer

bugfix: srl_tail_inc in submit, not in endio.
fix warning
temp...
buffer: add pre-alloc function & completion
...tail_inc in endio?