MFC r254945:
When allocating a pbuf for the cluster write, do not sleep waiting
for the available pbuf when passed vnode is backing md(4). Other i/o
directed to the same md device might already hold pbufs, and then we
could deadlock since only our progress can free a pbuf needed for
wakeup.
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.
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 r254018:
Pass variables prefixed with both LD_ and LD_32_ to the run-time linker.
This prevents unintentional execution of programs when running ldd(1) on
32-bit Linux binaries.
Merge remote-tracking branch 'upstream-github/stable/9' into stable/9