ynl: make the tooling check the license

The (only recently documented) expectation is that all specs
are under a certain license, but we don't actually enforce it.
What's worse we then go ahead and assume the license was right,
outputting the expected license into generated files.

Fixes: 37d9df22 ("ynl: re-license uniformly under GPL-2.0 OR BSD-3-Clause")
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/nlspec.py

@@ -274,6 +274,7 @@ class SpecFamily(SpecElement):
 
     Attributes:
         proto     protocol type (e.g. genetlink)
+        license   spec license (loaded from an SPDX tag on the spec)
 
         attr_sets  dict of attribute sets
         msgs       dict of all messages (index by name)
@@ -283,6 +284,13 @@ class SpecFamily(SpecElement):
     """
     def __init__(self, spec_path, schema_path=None):
         with open(spec_path, "r") as stream:
+            prefix = '# SPDX-License-Identifier: '
+            first = stream.readline().strip()
+            if not first.startswith(prefix):
+                raise Exception('SPDX license tag required in the spec')
+            self.license = first[len(prefix):]
+
+            stream.seek(0)
             spec = yaml.safe_load(stream)
 
         self._resolution_list = []

tools/net/ynl/ynl-gen-c.py

@@ -2059,6 +2059,10 @@ def main():
 
     try:
         parsed = Family(args.spec)
+        if parsed.license != '((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)':
+            print('Spec license:', parsed.license)
+            print('License must be: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)')
+            os.sys.exit(1)
     except yaml.YAMLError as exc:
         print(exc)
         os.sys.exit(1)
@@ -2067,13 +2071,10 @@ def main():
     cw = CodeWriter(BaseNlLib(), out_file)
 
     _, spec_kernel = find_kernel_root(args.spec)
-    if args.mode == 'uapi':
-        cw.p('/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */')
+    if args.mode == 'uapi' or args.header:
+        cw.p(f'/* SPDX-License-Identifier: {parsed.license} */')
     else:
-        if args.header:
-            cw.p('/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */')
-        else:
-            cw.p('// SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)')
+        cw.p(f'// SPDX-License-Identifier: {parsed.license}')
     cw.p("/* Do not edit directly, auto-generated from: */")
     cw.p(f"/*\t{spec_kernel} */")
     cw.p(f"/* YNL-GEN {args.mode} {'header' if args.header else 'source'} */")