Linux 4.5 compat: Use xattr_handler->name for acl

Linux 4.5 added member "name" to xattr_handler. xattr_handler which matches to
whole name rather than prefix should use "name" instead of "prefix".
Otherwise, kernel will return with EINVAL when it tries to resolve handlers.

Also, we remove the strcmp checks when xattr_handler has name, because
xattr_resolve_name will do the check for us.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4549
Closes #4537

config/kernel-xattr-handler.m4

@@ -32,6 +32,31 @@ AC_DEFUN([ZFS_AC_KERNEL_CONST_XATTR_HANDLER], [
 	])
 ])
 
+dnl #
+dnl # 4.5 API change,
+dnl # struct xattr_handler added new member "name".
+dnl # xattr_handler which matches to whole name rather than prefix should use
+dnl # "name" instead of "prefix", e.g. "system.posix_acl_access"
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_XATTR_HANDLER_NAME], [
+	AC_MSG_CHECKING([whether xattr_handler has name])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/xattr.h>
+
+		static const struct xattr_handler
+		    xops __attribute__ ((unused)) = {
+			.name = XATTR_NAME_POSIX_ACL_ACCESS,
+		};
+	],[
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_XATTR_HANDLER_NAME, 1,
+		    [xattr_handler has name])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
 dnl #
 dnl # Supported xattr handler get() interfaces checked newest to oldest.
 dnl #

config/kernel.m4

@@ -32,6 +32,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_GET_GENDISK
 	ZFS_AC_KERNEL_DISCARD_GRANULARITY
 	ZFS_AC_KERNEL_CONST_XATTR_HANDLER
+	ZFS_AC_KERNEL_XATTR_HANDLER_NAME
 	ZFS_AC_KERNEL_XATTR_HANDLER_GET
 	ZFS_AC_KERNEL_XATTR_HANDLER_SET
 	ZFS_AC_KERNEL_XATTR_HANDLER_LIST