parallel pool import

[grwilson]

This commit allow spa_load() to drop the spa_namespace_lock so that imports can happen concurrently. Prior to dropping the spa_namespace_lock, the import logic will set the spa_load_thread value to track the thread which is doing the import.

Consumers of spa_lookup() retain the same behavior by blocking when either a thread is holding the spa_namespace_lock or the spa_load_thread value is set. This will ensure that critical concurrent operations cannot take place while a pool is being imported.

The zpool command is enhanced to provide multi-threaded support when invoking zpool import -a.

Lastly, zinject provides a mechanism to insert artificial delays when importing a pool and new zfs tests are added to verify parallel import functionality.

Contributions-by: Don Brady don.brady@klarasystems.com

[mmatuska]

@grwilson When compiling 32-bit compat libraries on FreeBSD there is a cast error in

zfs/module/zfs/spa.c

Lines 6774 to 6775 in b28461b

	(void) snprintf(name, MAXPATHLEN, "%s-%llx-%s",
	TRYIMPORT_NAME, (u_longlong_t)curthread, poolname);

/usr/local/bin/x86_64-unknown-freebsd14.0-gcc13 -march=i686 -mmmx -msse -msse2 -m32    -DCOMPAT_LIBCOMPAT=\"32\"  -DCOMPAT_libcompat=\"32\"  -DCOMPAT_LIB32  --sysroot=/tmp/obj/workspace/src/amd64.amd64/tmp  -B/usr/local/x86_64-unknown-freebsd14.0/bin/ -B/tmp/obj/workspace/src/amd64.amd64/tmp/usr/lib32  -O2 -pipe -fno-common -DHAVE_SSE2       -DHAVE_SSE3 -DIN_BASE  -I/workspace/src/sys/contrib/openzfs/include  -I/workspace/src/sys/contrib/openzfs/lib/libspl/include  -I/workspace/src/sys/contrib/openzfs/lib/libspl/include/os/freebsd  -I/workspace/src/sys  -I/workspace/src/sys/contrib/openzfs/include/os/freebsd/zfs  -I/workspace/src/cddl/compat/opensolaris/include  -I/workspace/src/sys/contrib/openzfs/module/icp/include  -include /workspace/src/sys/contrib/openzfs/include/os/freebsd/spl/sys/ccompile.h  -DHAVE_ISSETUGID  -include /workspace/src/sys/modules/zfs/zfs_config.h  -I/workspace/src/sys/modules/zfs  -I/workspace/src/sys/contrib/openzfs/include/os/freebsd/zfs  -DLIB_ZPOOL_BUILD -DZFS_DEBUG -DWANTS_MUTEX_OWNED -I/workspace/src/lib/libpthread/thread -I/workspace/src/lib/libpthread/sys -I/workspace/src/lib/libthr/arch/i386/include -g -DDEBUG=1  -DNEED_SOLARIS_BOOLEAN -g -MD  -MF.depend.spa.o -MTspa.o -std=iso9899:1999 -Wno-format-zero-length -fstack-protector-strong -Wsystem-headers -Werror -Wall -Wno-format-y2k -Wno-uninitialized -Wno-pointer-sign -Wdate-time -Wno-error=address -Wno-error=array-bounds -Wno-error=attributes -Wno-error=bool-compare -Wno-error=cast-align -Wno-error=clobbered -Wno-error=deprecated-declarations -Wno-error=enum-compare -Wno-error=extra -Wno-error=logical-not-parentheses -Wno-error=strict-aliasing -Wno-error=uninitialized -Wno-error=unused-function -Wno-error=unused-value -Wno-error=empty-body -Wno-error=maybe-uninitialized -Wno-error=nonnull-compare -Wno-error=shift-negative-value -Wno-error=tautological-compare -Wno-error=unused-const-variable -Wno-error=bool-operation -Wno-error=deprecated -Wno-error=expansion-to-defined -Wno-error=format-overflow -Wno-error=format-truncation -Wno-error=implicit-fallthrough -Wno-error=int-in-bool-context -Wno-error=memset-elt-size -Wno-error=noexcept-type -Wno-error=nonnull -Wno-error=pointer-compare -Wno-error=stringop-overflow -Wno-error=aggressive-loop-optimizations -Wno-error=cast-function-type -Wno-error=catch-value -Wno-error=multistatement-macros -Wno-error=restrict -Wno-error=sizeof-pointer-memaccess -Wno-error=stringop-truncation -Wno-error=overflow -Wno-return-type -Wno-unknown-pragmas -Wno-address-of-packed-member  -fms-extensions     -c /workspace/src/sys/contrib/openzfs/module/zfs/spa.c -o spa.o
--- all_subdir_cddl/lib/libzpool ---
/workspace/src/sys/contrib/openzfs/module/zfs/spa.c: In function 'spa_tryimport':
/workspace/src/sys/contrib/openzfs/module/zfs/spa.c:6775:29: error: cast from pointer to integer of different size [-Werror=pointer-to-int-cast]
 6775 |             TRYIMPORT_NAME, (u_longlong_t)curthread, poolname);
      |                             ^