The block driver protocol and libblockdriver's bdr_ioctl hook are
changed, as well as the users of this hook. Other parts of the system
are expected to change accordingly eventually, since the ioctl(2)
prototype has been aligned with NetBSD's.
Change-Id: Ide46245b22cfa89ed267a38088fb0ab7696eba92
The implementation is in libblockdriver, and works transparently for
all block drivers. The new btrace(8) tool can be used to control block
tracing; see ``man btrace'' for details.