[PATCH 3/3] scripts: forbid use of arbitrary SPDX tags besides license identifiers

["Daniel P. Berrangé" <berrange@redhat.com>]

While SPDX-License-Identifier is a well known SPDX tag, there are a
great many more besides that[1]. This are around making machine readable
metadata available to the 'reuse' tool and similar for things like
author names, copyright owners, and much more. It is even possible to
define source file line groups and apply different SPDX tags to just
that region of code.

At this time we're only interested in adopting SPDX for recording the
licensing info, so detect & reject any other SPDX metadata. If we want
to explicitly collect extra data in SPDX format, we can evaluate each
case on its merits.

[1] https://spdx.github.io/spdx-spec/v2.2.2/file-tags/
    https://spdx.github.io/spdx-spec/v2.2.2/file-information/

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 scripts/checkpatch.pl | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index cd1ed90f4c..5ad2d4ca2e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1707,6 +1707,18 @@ sub process {
 		    &checkspdx($realfile, $1);
 		}
 
+		if ($rawline =~ m,(SPDX-[a-zA-Z0-9-_]+):,) {
+		    my $tag = $1;
+		    my @permitted = qw(
+			SPDX-License-Identifier
+		    );
+
+		    unless (grep { /^$tag$/ } @permitted) {
+			ERROR("Tag $tag not permitted in QEMU code, valid " .
+			      "choices are: " . join(", ", @permitted));
+		    }
+		}
+
 # Check for wrappage within a valid hunk of the file
 		if ($realcnt != 0 && $line !~ m{^(?:\+|-| |\\ No newline|$)}) {
 			ERROR("patch seems to be corrupt (line wrapped?)\n" .
-- 
2.46.0