Merge OpenZFS support in to HEAD.

The primary benefit is maintaining a completely shared
code base with the community allowing FreeBSD to receive
new features sooner and with less effort.

I would advise against doing 'zpool upgrade'
or creating indispensable pools using new
features until this change has had a month+
to soak.

Work on merging FreeBSD support in to what was
at the time "ZFS on Linux" began in August 2018.
I first publicly proposed transitioning FreeBSD
to (new) OpenZFS on December 18th, 2018. FreeBSD
support in OpenZFS was finally completed in December
2019. A CFT for downstreaming OpenZFS support in
to FreeBSD was first issued on July 8th. All issues
that were reported have been addressed or, for
a couple of less critical matters there are
pull requests in progress with OpenZFS. iXsystems
has tested and dogfooded extensively internally.
The TrueNAS 12 release is based on OpenZFS with
some additional features that have not yet made
it upstream.

Improvements include:
  project quotas, encrypted datasets,
  allocation classes, vectorized raidz,
  vectorized checksums, various command line
  improvements, zstd compression.

Thanks to those who have helped along the way:
Ryan Moeller, Allan Jude, Zack Welch, and many
others.

Sponsored by:	iXsystems, Inc.
Differential Revision:	https://reviews.freebsd.org/D25872

Makefile.inc1

@@ -2442,7 +2442,7 @@ _btxld=		usr.sbin/btxld
 # Rebuild ctfconvert and ctfmerge to avoid difficult-to-diagnose failures
 # resulting from missing bug fixes or ELF Toolchain updates.
 .if ${MK_CDDL} != "no"
-_dtrace_tools= cddl/lib/libctf cddl/usr.bin/ctfconvert \
+_dtrace_tools= cddl/lib/libctf cddl/lib/libspl cddl/usr.bin/ctfconvert \
     cddl/usr.bin/ctfmerge
 .endif
 
@@ -2756,7 +2756,12 @@ _prebuild_libs=	${_kerberos5_lib_libasn1} \
 		${_cddl_lib_libumem} ${_cddl_lib_libnvpair} \
 		${_cddl_lib_libuutil} \
 		${_cddl_lib_libavl} \
+		${_cddl_lib_libicp} \
+		${_cddl_lib_libicp_rescue} \
+		${_cddl_lib_libspl} \
+		${_cddl_lib_libtpool} \
 		${_cddl_lib_libzfs_core} ${_cddl_lib_libzfs} \
+		${_cddl_lib_libzutil} \
 		${_cddl_lib_libctf} \
 		lib/libufs \
 		lib/libutil lib/libpjdlog ${_lib_libypclnt} lib/libz lib/msun \
@@ -2826,21 +2831,34 @@ _cddl_lib_libumem= cddl/lib/libumem
 _cddl_lib_libnvpair= cddl/lib/libnvpair
 _cddl_lib_libavl= cddl/lib/libavl
 _cddl_lib_libuutil= cddl/lib/libuutil
+_cddl_lib_libspl= cddl/lib/libspl
+
+cddl/lib/libuutil__L: cddl/lib/libavl__L cddl/lib/libspl__L
+
 .if ${MK_ZFS} != "no"
+_cddl_lib_libicp= cddl/lib/libicp
+_cddl_lib_libicp_rescue= cddl/lib/libicp_rescue
+_cddl_lib_libtpool= cddl/lib/libtpool
+_cddl_lib_libzutil= cddl/lib/libzutil
 _cddl_lib_libzfs_core= cddl/lib/libzfs_core
 _cddl_lib_libzfs= cddl/lib/libzfs
 
+cddl/lib/libtpool__L: cddl/lib/libspl__L
+
+cddl/lib/libzutil__L: cddl/lib/libavl__L cddl/lib/libtpool__L
+
 cddl/lib/libzfs_core__L: cddl/lib/libnvpair__L
 
 cddl/lib/libzfs__L: cddl/lib/libzfs_core__L lib/msun__L lib/libutil__L
 cddl/lib/libzfs__L: lib/libthr__L lib/libmd__L lib/libz__L cddl/lib/libumem__L
 cddl/lib/libzfs__L: cddl/lib/libuutil__L cddl/lib/libavl__L lib/libgeom__L
+cddl/lib/libzfs__L: cddl/lib/libnvpair__L cddl/lib/libzutil__L
 
 lib/libbe__L: cddl/lib/libzfs__L
 .endif
 _cddl_lib_libctf= cddl/lib/libctf
 _cddl_lib= cddl/lib
-cddl/lib/libctf__L: lib/libz__L
+cddl/lib/libctf__L: lib/libz__L cddl/lib/libspl__L
 .endif
 # cddl/lib/libdtrace requires lib/libproc and lib/librtld_db
 _prebuild_libs+=	lib/libprocstat lib/libproc lib/librtld_db

cddl/compat/opensolaris/include/fcntl.h

@@ -32,7 +32,9 @@
 
 #include_next <fcntl.h>
 
+#ifndef open64
 #define open64(...)	open(__VA_ARGS__)
+#endif
 #define openat64(...)	openat(__VA_ARGS__)
 
 #endif

cddl/contrib/opensolaris/cmd/lockstat/sym.c

@@ -54,6 +54,7 @@
 #endif
 #include <sys/cpuvar.h>
 
+
 typedef struct syment {
 	uintptr_t	addr;
 	char		*name;
@@ -72,6 +73,11 @@ static char maxsymname[64];
 #endif
 #endif
 
+#define __sElfN(x)       typedef __CONCAT(__CONCAT(__CONCAT(Elf,__ELF_WORD_SIZE),_),x) x
+__sElfN(Sym);
+__sElfN(Shdr);
+#define	elf_getshdr		__elfN(getshdr)
+
 static void
 add_symbol(char *name, uintptr_t addr, size_t size)
 {