Chain bio completions
void bio_chain(struct bio * bio, struct bio * parent);
bio
the target bio
parent
the bio's parent bio
The caller won't have a bi_end_io called when bio completes - instead, parent's bi_end_io won't be called until both parent and bio have completed; the chained bio will also be freed when it completes.
The caller must not set bi_private or bi_end_io in bio.