MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

devd: Remove unnecessary empty default constructors.

Submitted by: Christoph Mallon <christoph.mallon@gmx.de>
Approved by: cperciva (mentor)

devd: Remove empty virtual destructor from class, which has noch subclasses.

Submitted by: Christoph Mallon <christoph.mallon@gmx.de>
Approved by: cperciva (mentor)

devd: Use the standard constructor of std::string instead of string("").

Submitted by: Christoph Mallon <christoph.mallon@gmx.de>
Approved by: cperciva (mentor)

Constify where possible.

Approved by: cperciva (mentor)

Improve devd startup time, by tweaking some string handling routines that are
heavily used when parsing config files. Mostly these changes avoid making
temporary copies of the strings, and avoid doing byte at a time append
operations, on the most-used code path.

On a 1.2 GHz ARM processor this reduces the time to parse the config files
from 13 to 6 seconds.

Reviewed by: imp
Approved by: cognet (mentor)

Prefer the use of initalizer lists to ctor assignment.

Approved by: cperciva
MFC after: 2 weeks

Constify where possible

Approved by: cperciva
MFC after: 2 weeks

In sbin/devd/devd.h, 'event_proc' and 'eps' are declared as structs. In
devd.hh, there are redeclared as classes. Fix the inconsistency.

MFC after: 1 week

- Add support for a "!" character in regex matching in devd(8). It inverts
the logic (true/false) of the matching.

- Add "!usbus[0-9]+" to IFNET ATTACH notification handler in the default
devd.conf to prevent rc.d/netif from running when usbus[0-9]+ is attached.

Reviewed by: imp

Expand system into my_system, and add the necessary tidyness that we
need. Close the pidfile. Then close all descriptors >= 3 to avoid
information leakage to children.

This solves the problem of not being able to restart devd when you
have, for example, a dhclient forked to configure your network...

MFC after: 3 days

Minor initialization change to not trigger bogus gcc warning about
passing literal strings to the constructors of string.

Use pidfile(3).

OK'ed by: imp

Add the ability to match the on a media type of the device in question.

Submitted by: sam
Approved by: re (scottl)

Parse the ! lines that will soon be coming from the kernel. These are
a generalized notification mechanism for subsystems wishing to report
events.

Revieded by: njl

# The kernel side seems like it might be causing panics for me, but should
# be forthcoming shortly.

Create a new C++ header file called devd.hh which has all the class
definitions in it. Begin to document the classes that we use, and how
they interrelate (using comments that I can use with doxygen to
automatically generate docs with).