Revert r314937 as anonymous unions in GCC don't seem to work.

This has been breaking the powerpc(LINT64 at least) for quite a while now.

Reported by: emaste

Revert 294545:
Bringing back ext4: add support for reading sparse files

Add GCC_MS_EXTENSIONS to the CFLAGS in the module to make the old GCC in
base happy. This workaround is only required in stable/10.

MFC r294504, r294652, r294653, r294655:

ext2fs: Bring back the htree dir_index implementation.

The htree dir_index is perhaps one of the most characteristic
features of the linux ext3 implementation. It was removed
in r281670, due to repeated bug reports.

Damjan Jovanic detected and fixed three bugs and did some
stress testing by building Apache OpenOffice on top of it
so it is now in good shape to bring back.

Differential Revision: https://reviews.freebsd.org/D5007

Submitted by: Damjan Jovanovic
Reviewed by: pfg
RelNotes: yes

MFC r281670, r281703:
Drop experimental ext2fs dir_index support.

The htree directory index is a highly desirable feature for research
purposes and was meant to improve performance in our ext2/3 driver.
Unfortunately our implementation has two problems:

- It never really delivered any performance improvement.
- It appears to corrupt the filesystem in undetermined circumstances.

Strictly speaking dir_index is not required for read/write support in
ext2/3 and our limited ext4 support still works fine without it.

Regain stability in the ext2 driver by removing it. We may need it back
(fixed) if we want to support encrypted ext4 support but thanks to the
wonders of version control we can always revert this change and bring it
back.

PR: 191895
PR: 198731
PR: 199309

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

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

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

Initial implementation of the HTree directory index.

This is a port of NetBSD's GSoC 2012 Ext3 HTree directory indexing
by Vyacheslav Matyushin. It was cleaned up and enhanced for FreeBSD
by Zheng Liu (lz@).

This is an excellent example of work shared among different projects:
Vyacheslav was able to look at an early prototype from Zheng Liu who
was also able to check the code from Haiku (with permission).

As in linux, the feature is not available by default and must be
enabled explicitly with tune2fs. We still do not support the
workarounds required in readdir for NFS.

Submitted by: Zheng Liu
Tested by: Mike Ma
Sponsored by: Google Inc.
MFC after: 1 week

Sync with several changes in UFS/FFS:
- 77115: Implement support for O_DIRECT.
- 98425: Fix a performance issue introduced in 70131 that was causing
reads before writes even when writing full blocks.
- 98658: Rename the BALLOC flags from B_* to BA_* to avoid confusion with
the struct buf B_ flags.
- 100344: Merge the BA_ and IO_ flags so so that they may both be used in
the same flags word. This merger is possible by assigning the IO_ flags
to the low sixteen bits and the BA_ flags the high sixteen bits.
- 105422: Fix a file-rewrite performance case.
- 129545: Implement IO_INVAL in VOP_WRITE() by marking the buffer as
"no cache".
- Readd the DOINGASYNC() macro and use it to control asynchronous writes.
Change i-node updates to honor DOINGASYNC() instead of always being
synchronous.
- Use a PRIV_VFS_RETAINSUGID check instead of checking cr_uid against 0
directly when deciding whether or not to clear suid and sgid bits.

Submitted by: Pedro F. Giffuni giffunip at yahoo

Bring in the ext2fs work done by Aditya Sarawgi during and after Google Summer
of Code 2009:

- BSDL block and inode allocation policies for ext2fs. This involves the use
FFS1 style block and inode allocation for ext2fs. Preallocation was removed
since it was GPL'd.
- Make ext2fs MPSAFE by introducing locks to per-mount datastructures.
- Fixes for kern/122047 PR.
- Various small bugfixes.
- Move out of gnu/ directory.

Sponsored by: Google Inc.
Submitted by: Aditya Sarawgi <sarawgi.aditya AT SPAMFREE gmail DOT com>

Move ext2fs from src/gnu to src/gnu/fs.
Discussed on arch@.

Reviewed by: kan
Approved by: re (blanket), kan

Use vfs_hash() instead of home-rolled

Complete the separation of ext2fs from ufs by copying the remaining
shared code and converting all ufs references. Originally it may
have made sense to share common features between the two filesystems,
but recently it has only caused problems, the UFS2 work being the
final straw.

All UFS_* indirect calls are now direct calls to ext2_* functions,
and ext2fs-specific mount and inode structures have been introduced.

Fixed some style bugs (disordered SRCS and garbage comment near EOF).

Drop <bsd.man.mk> support from <bsd.kmod.mk>.

Not objected to by: -current

Add ext2fs module