scripts: documentation-file-ref-check: improve :doc: handling

There are some issues at the script with regards to :doc:
tags:

- It doesn't escape files under Documentation/sphinx,
  leading to false positives;
- It doesn't handle root URLs, like :doc:`/x86/boot`;
- It doesn't output the file with a bad reference.

Address those things, in order to remove false positives
from the list of problems.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/documentation-file-ref-check

@@ -51,7 +51,9 @@ open IN, "git grep ':doc:\`' Documentation/|"
      or die "Failed to run git grep";
 while (<IN>) {
 	next if (!m,^([^:]+):.*\:doc\:\`([^\`]+)\`,);
+	next if (m,sphinx/,);
 
+	my $file = $1;
 	my $d = $1;
 	my $doc_ref = $2;
 
@@ -60,7 +62,12 @@ while (<IN>) {
 	$d =~ s,(.*/).*,$1,;
 	$f =~ s,.*\<([^\>]+)\>,$1,;
 
-	$f ="$d$f.rst";
+	if ($f =~ m,^/,) {
+		$f = "$f.rst";
+		$f =~ s,^/,Documentation/,;
+	} else {
+		$f = "$d$f.rst";
+	}
 
 	next if (grep -e, glob("$f"));
 
@@ -69,7 +76,7 @@ while (<IN>) {
 	}
 	$doc_fix++;
 
-	print STDERR "$f: :doc:`$doc_ref`\n";
+	print STDERR "$file: :doc:`$doc_ref`\n";
 }
 close IN;