Make Python detection optional and more portable

Previously, --without-python would cause ./configure to fail. Now it is
able to proceed, and the Python scripts will not be built.

Use portable parameter expansion matching instead of nonstandard
substring matching to detect the Python version.  This test is
duplicated in several places, so define a function for it.

Don't assume the full path to binaries, since different platforms do
install things in different places.  Use AC_CHECK_PROGS instead.

When building without Python, also build without pyzfs.

Sponsored by: iXsystems, Inc.
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Richard Laager <[email protected]>
Reviewed-by: Eli Schwartz <[email protected]>
Signed-off-by: Ryan Moeller <[email protected]>
Closes #8809 
Closes #8731 

3 files changed, 39 insertions, 24 deletions

diff --git a/cmd/Makefile.am b/cmd/Makefile.am
index 9dd7b8b4f..0d990789b 100644
--- a/cmd/Makefile.am
+++ b/cmd/Makefile.am
@@ -1,3 +1,8 @@
 SUBDIRS  = zfs zpool zdb zhack zinject zstreamdump ztest
-SUBDIRS += mount_zfs fsck_zfs zvol_id vdev_id arcstat dbufstat zed
-SUBDIRS += arc_summary raidz_test zgenhostid
+SUBDIRS += fsck_zfs vdev_id raidz_test zgenhostid
+
+if USING_PYTHON
+SUBDIRS += arcstat arc_summary dbufstat
+endif
+
+SUBDIRS += mount_zfs zed zvol_id
diff --git a/config/always-python.m4 b/config/always-python.m4
index 858ab7b01..7cfefd9eb 100644
--- a/config/always-python.m4
+++ b/config/always-python.m4
@@ -13,6 +13,17 @@ AC_DEFUN([ZFS_AC_PYTHON_VERSION], [
 ])
 
 dnl #
+dnl # ZFS_AC_PYTHON_VERSION_IS_2
+dnl # ZFS_AC_PYTHON_VERSION_IS_3
+dnl #
+dnl # Tests if the $PYTHON_VERSION matches 2.x or 3.x.
+dnl #
+AC_DEFUN([ZFS_AC_PYTHON_VERSION_IS_2],
+	[test "${PYTHON_VERSION%%\.*}" = "2"])
+AC_DEFUN([ZFS_AC_PYTHON_VERSION_IS_3],
+	[test "${PYTHON_VERSION%%\.*}" = "3"])
+
+dnl #
 dnl # ZFS_AC_PYTHON_MODULE(module_name, [action-if-true], [action-if-false])
 dnl #
 dnl # Checks for Python module. Freely inspired by AX_PYTHON_MODULE
@@ -46,42 +57,36 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_PYTHON], [
 		[with_python=check])
 
 	AS_CASE([$with_python],
-		[check],
-		[AS_IF([test -x /usr/bin/python3],
-			[PYTHON="python3"],
-			[AS_IF([test -x /usr/bin/python2],
-				[PYTHON="python2"],
-				[PYTHON=""]
-			)]
-		)],
+		[check], [AC_CHECK_PROGS([PYTHON], [python3 python2], [:])],
 		[2*], [PYTHON="python${with_python}"],
 		[*python2*], [PYTHON="${with_python}"],
 		[3*], [PYTHON="python${with_python}"],
 		[*python3*], [PYTHON="${with_python}"],
-		[no], [PYTHON=""],
+		[no], [PYTHON=":"],
 		[AC_MSG_ERROR([Unknown --with-python value '$with_python'])]
 	)
 
-	AS_IF([$PYTHON --version >/dev/null 2>&1], [ /bin/true ], [
-		AC_MSG_ERROR([Cannot find $PYTHON in your system path])
+	AS_IF([test $PYTHON != :], [
+		AS_IF([$PYTHON --version >/dev/null 2>&1],
+			[AM_PATH_PYTHON([2.6], [], [:])],
+			[AC_MSG_ERROR([Cannot find $PYTHON in your system path])]
+		)
 	])
-
-	AM_PATH_PYTHON([2.6], [], [:])
 	AM_CONDITIONAL([USING_PYTHON], [test "$PYTHON" != :])
-	AM_CONDITIONAL([USING_PYTHON_2], [test "${PYTHON_VERSION:0:2}" = "2."])
-	AM_CONDITIONAL([USING_PYTHON_3], [test "${PYTHON_VERSION:0:2}" = "3."])
+	AM_CONDITIONAL([USING_PYTHON_2], [ZFS_AC_PYTHON_VERSION_IS_2])
+	AM_CONDITIONAL([USING_PYTHON_3], [ZFS_AC_PYTHON_VERSION_IS_3])
 
 	dnl #
 	dnl # Minimum supported Python versions for utilities:
 	dnl # Python 2.6.x, or Python 3.4.x
 	dnl #
-	AS_IF([test "${PYTHON_VERSION:0:2}" = "2."], [
-		ZFS_AC_PYTHON_VERSION([>= '2.6'], [ /bin/true ],
+	AS_IF([ZFS_AC_PYTHON_VERSION_IS_2], [
+		ZFS_AC_PYTHON_VERSION([>= '2.6'], [ true ],
 			[AC_MSG_ERROR("Python >= 2.6.x is not available")])
 	])
 
-	AS_IF([test "${PYTHON_VERSION:0:2}" = "3."], [
-		ZFS_AC_PYTHON_VERSION([>= '3.4'], [ /bin/true ],
+	AS_IF([ZFS_AC_PYTHON_VERSION_IS_3], [
+		ZFS_AC_PYTHON_VERSION([>= '3.4'], [ true ],
 			[AC_MSG_ERROR("Python >= 3.4.x is not available")])
 	])
 
diff --git a/config/always-pyzfs.m4 b/config/always-pyzfs.m4
index d74d6f1a7..6f32e98fe 100644
--- a/config/always-pyzfs.m4
+++ b/config/always-pyzfs.m4
@@ -18,7 +18,12 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_PYZFS], [
 			DEFINE_PYZFS='--without pyzfs'
 		])
 	], [
-		DEFINE_PYZFS=''
+		AS_IF([test $PYTHON != :], [
+			DEFINE_PYZFS=''
+		], [
+			enable_pyzfs=no
+			DEFINE_PYZFS='--without pyzfs'
+		])
 	])
 	AC_SUBST(DEFINE_PYZFS)
 
@@ -26,10 +31,10 @@ AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_PYZFS], [
 	dnl # Require python-devel libraries
 	dnl #
 	AS_IF([test "x$enable_pyzfs" = xcheck  -o "x$enable_pyzfs" = xyes], [
-		AS_IF([test "${PYTHON_VERSION:0:2}" = "2."], [
+		AS_IF([ZFS_AC_PYTHON_VERSION_IS_2], [
 			PYTHON_REQUIRED_VERSION=">= '2.7.0'"
 		], [
-			AS_IF([test "${PYTHON_VERSION:0:2}" = "3."], [
+			AS_IF([ZFS_AC_PYTHON_VERSION_IS_3], [
 				PYTHON_REQUIRED_VERSION=">= '3.4.0'"
 			], [
 				AC_MSG_ERROR("Python $PYTHON_VERSION unknown")