There seems to be a trend where a nice, general and symmetrical user
interfaces in the kernel will be made less capable by the removal of
unused parts, just because no in-kernel code is using the interface to
its full potential yet.

If we could get changes into the kernel more quickly, then we wouldn't
have the rug pulled out from under us (I hope).

commit 5705f7021748a69d84d6567e68e8851dab551464
Author: NeilBrown <neilb@suse.de>
Date:   Tue Sep 25 12:35:59 2007 +0200

    Introduce rq_for_each_segment replacing rq_for_each_bio
    
    Every usage of rq_for_each_bio wraps a usage of
    bio_for_each_segment, so these can be combined into
    rq_for_each_segment.