Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Include sys/sbuf.h directly.

Reviewed by: pjd

Provide a set of sysctls and tunables to disable device node creation
for specific "kinds" of disk labels - for example, GPT UUIDs. Reason
for this is that sometimes, other GEOM classes attach to these device
nodes instead of the proper ones - e.g. they attach to /dev/gptid/XXX
instead of /dev/ada0p2, which is annoying.

Reviewed by: pjd (earlier version)
MFC after: 1 month

Fix tabs, slightly improve comments.

Approved by: gnn (mentor) (original)
Noticed by: stas

Add support for labels derived from GPT metadata.

Approved by: gnn (mentor)
Reviewed by: pjd
PR: 128398
Submitted by: Marius Nuennerich < marius at nuenneri.ch >