sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

Improve extents verification logic.

It is possible to walk thru inode extents if EXT2FS_PRINT_EXTENTS
macro is defined. The extents headers magics and physical blocks
ranges are checked during extents walk.

Reviewed by: pfg
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D29932

Add BE architectures support.

Author of most initial version: pfg (https://reviews.freebsd.org/D23259)

Reviewed by: pfg
MFC after: 3 months

Differential Revision: https://reviews.freebsd.org/D24685

ext2fs: Initial version of DTrace support.

Reviewed by: pfg, gnn
MFC after: 1 week

Differential Revision: https://reviews.freebsd.org/D19848

Fix EXT2FS_DEBUG definition usage.

Reviewed by: pfg
MFC after: 3 months

Differential Revision: https://reviews.freebsd.org/D15394

Add metadata_csum feature support.

Reviewed by: pfg (mentor)
Approved by: pfg (mentor)
MFC after: 6 months

Differential Revision: https://reviews.freebsd.org/D13810

Add 64bit feature support.

Reviewed by: kevlo, pfg (mentor)
Approved by: pfg (mentor)
MFC after: 6 months

Differential Revision: https://reviews.freebsd.org/D11530

sys/fs: further 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.

Add inital extents read-write support.

Approved by: pfg (mentor)
MFC after: 6 months
RelNotes: Yes

Differential Revision: https://reviews.freebsd.org/D12087

style(9) cleanups.

Just to reduce some of the issues found with indent(1).

MFC after: 1 week

ext2fs(5): Cosmetic cleanups, mostly to the ext4 code.

Obtained from: NetBSD

Ext4: Use boolean type instead of '0' and '1'

There are precedents of uses of bool in the kernel and
it is incorrect style to use integers as replacement for
a boolean type.

ext4: add support for reading sparse files

Add support for sparse files in ext4. Also implement read-ahead, which
greatly increases the performance when transferring files from ext4.

Both features implemented by Damjan Jovanovic.

PR: 205816
MFC after: 1 week

ext2fs: use of tab vs spaces.

Consistently use a single tab after a #define as mentioned in style(9).
Use tabs instead of space for indenting.
Fix a typo: "hash_vesion".

No functional change.

MFC after: 3 days

Add read-only support for extents in ext2fs.

Basic support for extents was implemented by Zheng Liu as part
of his Google Summer of Code in 2010. This support is read-only
at this time.

In addition to extents we also support the huge_file extension
for read-only purposes. This works nicely with the additional
support for birthtime/nanosec timestamps and dir_index that
have been added lately.

The implementation may not work for all ext4 filesystems as
it doesn't support some features that are being enabled by
default on recent linux like flex_bg. Nevertheless, the feature
should be very useful for migration or simple access in
filesystems that have been converted from ext2/3 or don't use
incompatible features.

Special thanks to Zheng Liu for his dedication and continued
work to support ext2 in FreeBSD.

Submitted by: Zheng Liu (lz@)
Reviewed by: Mike Ma, Christoph Mallon (previous version)
Sponsored by: Google Inc.
MFC after: 3 weeks