kobj: allow multiple inheritance with per-class softcHEADmain

Add support for hierarchical softc layout so that a leaf class and each
of its base classes owns a private softc region inside a single
allocation.

device_get_softc_class(dev, cls) returns a pointer to the softc that
belongs to the requested class.  The classic device_get_softc() still
returns the leaf softc and remains fully compatible with existing
drivers.

Existing drivers are unaffected; they simply obtain a slightly larger
softc block when they inherit from base classes.

MFC after:	2 months
Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D59115

0 files changed, 0 insertions, 0 deletions