Running xdrgen on xdrgen/tests/test.x fails when
generating encoder or decoder functions for union
members of type _XdrString. It was because _XdrString
does not have a spec attribute like _XdrBasic,
leading to AttributeError.

This patch updates emit_union_case_spec_definition
and emit_union_case_spec_decoder/encoder to handle
_XdrString by assigning type_name = "char *" and
avoiding referencing to spec.

Testing: Fixed xdrgen tool was run on originally failing
test file (tools/net/sunrpc/xdrgen/tests/test.x) and now
completes without AttributeError. Modified xdrgen tool was
also run against nfs4_1.x (Documentation/sunrpc/xdr/nfs4_1.x).
The output header file matches with nfs4_1.h
(include/linux/sunrpc/xdrgen/nfs4_1.h).
This validates the patch for all XDR input files currently
within the kernel.

Changes since v2:
- Moved the shebang to the first line
- Removed SPDX header to match style of current xdrgen files

Changes since v1:
- Corrected email address in Signed-off-by.
- Wrapped patch description lines to 72 characters.

Signed-off-by: Khushal Chitturi <kc9282016@gmail.com>
---
 tools/net/sunrpc/xdrgen/generators/union.py   | 34 ++++++++++++++-----
 .../templates/C/union/encoder/string.j2       |  6 ++++
 2 files changed, 31 insertions(+), 9 deletions(-)
 create mode 100644 tools/net/sunrpc/xdrgen/templates/C/union/encoder/string.j2

diff --git a/tools/net/sunrpc/xdrgen/generators/union.py b/tools/net/sunrpc/xdrgen/generators/union.py
index 2cca00e279cd..ad1f214ef22a 100644
--- a/tools/net/sunrpc/xdrgen/generators/union.py
+++ b/tools/net/sunrpc/xdrgen/generators/union.py
@@ -8,7 +8,7 @@ from jinja2 import Environment
 from generators import SourceGenerator
 from generators import create_jinja2_environment, get_jinja2_template
 
-from xdr_ast import _XdrBasic, _XdrUnion, _XdrVoid, get_header_name
+from xdr_ast import _XdrBasic, _XdrUnion, _XdrVoid, _XdrString, get_header_name
 from xdr_ast import _XdrDeclaration, _XdrCaseSpec, public_apis, big_endian
 
 
@@ -40,13 +40,20 @@ def emit_union_case_spec_definition(
     """Emit a definition for an XDR union's case arm"""
     if isinstance(node.arm, _XdrVoid):
         return
-    assert isinstance(node.arm, _XdrBasic)
+    if isinstance(node.arm, _XdrString):
+        type_name = "char *"
+        classifier = ""
+    else:
+        type_name = node.arm.spec.type_name
+        classifier = node.arm.spec.c_classifier
+
+    assert isinstance(node.arm, (_XdrBasic, _XdrString))
     template = get_jinja2_template(environment, "definition", "case_spec")
     print(
         template.render(
             name=node.arm.name,
-            type=node.arm.spec.type_name,
-            classifier=node.arm.spec.c_classifier,
+            type=type_name,
+            classifier=classifier,
         )
     )
 
@@ -84,6 +91,12 @@ def emit_union_case_spec_decoder(
 
     if isinstance(node.arm, _XdrVoid):
         return
+    if isinstance(node.arm, _XdrString):
+        type_name = "char *"
+        classifier = ""
+    else:
+        type_name = node.arm.spec.type_name
+        classifier = node.arm.spec.c_classifier
 
     if big_endian_discriminant:
         template = get_jinja2_template(environment, "decoder", "case_spec_be")
@@ -92,13 +105,13 @@ def emit_union_case_spec_decoder(
     for case in node.values:
         print(template.render(case=case))
 
-    assert isinstance(node.arm, _XdrBasic)
+    assert isinstance(node.arm, (_XdrBasic, _XdrString))
     template = get_jinja2_template(environment, "decoder", node.arm.template)
     print(
         template.render(
             name=node.arm.name,
-            type=node.arm.spec.type_name,
-            classifier=node.arm.spec.c_classifier,
+            type=type_name,
+            classifier=classifier,
         )
     )
 
@@ -169,7 +182,10 @@ def emit_union_case_spec_encoder(
 
     if isinstance(node.arm, _XdrVoid):
         return
-
+    if isinstance(node.arm, _XdrString):
+        type_name = "char *"
+    else:
+        type_name = node.arm.spec.type_name
     if big_endian_discriminant:
         template = get_jinja2_template(environment, "encoder", "case_spec_be")
     else:
@@ -181,7 +197,7 @@ def emit_union_case_spec_encoder(
     print(
         template.render(
             name=node.arm.name,
-            type=node.arm.spec.type_name,
+            type=type_name,
         )
     )
 
diff --git a/tools/net/sunrpc/xdrgen/templates/C/union/encoder/string.j2 b/tools/net/sunrpc/xdrgen/templates/C/union/encoder/string.j2
new file mode 100644
index 000000000000..2f035a64f1f4
--- /dev/null
+++ b/tools/net/sunrpc/xdrgen/templates/C/union/encoder/string.j2
@@ -0,0 +1,6 @@
+{# SPDX-License-Identifier: GPL-2.0 #}
+{% if annotate %}
+		/* member {{ name }} (variable-length string) */
+{% endif %}
+		if (!xdrgen_encode_string(xdr, ptr->u.{{ name }}, {{ maxsize }}))
+			return false;
-- 
2.51.1