Strengthen Linux kernel capabilities detection

- Add `CONFIG_BLOCK` Linux config requirement to
  `ZFS_AC_KERNEL_CONFIG_DEFINED`. OpenZFS won't compile without
  that block device support due to large amount of functional
  dependencies on it.

- Remove dependency on `groups_alloc()` in
  `ZFS_AC_KERNEL_SRC_GROUP_INFO_GID` to circumvent the missing stub
  in Linux 4.X kernel headers.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: szubersk <[email protected]>
Closes #13351

config/kernel-config-defined.m4

@@ -19,19 +19,46 @@ AC_DEFUN([ZFS_AC_KERNEL_CONFIG_DEFINED], [
 		])
 	])
 
+	ZFS_AC_KERNEL_SRC_CONFIG_BLOCK
 	ZFS_AC_KERNEL_SRC_CONFIG_DEBUG_LOCK_ALLOC
 	ZFS_AC_KERNEL_SRC_CONFIG_TRIM_UNUSED_KSYMS
-	ZFS_AC_KERNEL_SRC_CONFIG_ZLIB_INFLATE
 	ZFS_AC_KERNEL_SRC_CONFIG_ZLIB_DEFLATE
+	ZFS_AC_KERNEL_SRC_CONFIG_ZLIB_INFLATE
 
 	AC_MSG_CHECKING([for kernel config option compatibility])
 	ZFS_LINUX_TEST_COMPILE_ALL([config])
 	AC_MSG_RESULT([done])
 
+	ZFS_AC_KERNEL_CONFIG_BLOCK
 	ZFS_AC_KERNEL_CONFIG_DEBUG_LOCK_ALLOC
 	ZFS_AC_KERNEL_CONFIG_TRIM_UNUSED_KSYMS
-	ZFS_AC_KERNEL_CONFIG_ZLIB_INFLATE
 	ZFS_AC_KERNEL_CONFIG_ZLIB_DEFLATE
+	ZFS_AC_KERNEL_CONFIG_ZLIB_INFLATE
+])
+
+dnl #
+dnl # Check CONFIG_BLOCK
+dnl #
+dnl # Verify the kernel has CONFIG_BLOCK support enabled.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_CONFIG_BLOCK], [
+	ZFS_LINUX_TEST_SRC([config_block], [
+		#if !defined(CONFIG_BLOCK)
+		#error CONFIG_BLOCK not defined
+		#endif
+	],[])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_CONFIG_BLOCK], [
+	AC_MSG_CHECKING([whether CONFIG_BLOCK is defined])
+	ZFS_LINUX_TEST_RESULT([config_block], [
+		AC_MSG_RESULT([yes])
+	],[
+		AC_MSG_RESULT([no])
+		AC_MSG_ERROR([
+	*** This kernel does not include the required block device support.
+	*** Rebuild the kernel with CONFIG_BLOCK=y set.])
+	])
 ])
 
 dnl #

config/kernel-group-info.m4

@@ -6,8 +6,8 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_GROUP_INFO_GID], [
 	ZFS_LINUX_TEST_SRC([group_info_gid], [
 		#include <linux/cred.h>
 	],[
-		struct group_info *gi = groups_alloc(1);
-		gi->gid[0] = KGIDT_INIT(0);
+		struct group_info gi __attribute__ ((unused)) = {};
+		gi.gid[0] = KGIDT_INIT(0);
 	])
 ])