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

Some linux distros put mount point into the ext2fs labels, such as '/', or
'/boot', which confuses the devfs code and can cause userland programs to
fail reading /dev/ext2fs directory with weird error code, such as any
program that uses pwlib.

Strip any leading slashes before feeding the label to the geom_label code.

Sponsored by: Sippy Software, Inc.

MFC after: 1 week

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

Verify if we can actually read the data at given offset.

Reported by: Martin <nakal@nurfuerspam.de>

Add code for Ext2FS and ReiserFS labels recognition.

Submitted by: Stanislav Sedov <stas@310.ru>
PR: kern/84638
MFC after: 1 week