checkpatch: add ethtool_sprintf rules

Add some warnings for using ethtool_sprintf() where a simple
ethtool_puts() would suffice.

The two cases are:

1) Use ethtool_sprintf() with just two arguments:
|       ethtool_sprintf(&data, driver[i].name);
or
2) Use ethtool_sprintf() with a standalone "%s" fmt string:
|       ethtool_sprintf(&data, "%s", driver[i].name);

The former may cause -Wformat-security warnings while the latter is just
not preferred. Both are safely in the category of warnings, not errors.
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

scripts/checkpatch.pl

@@ -7011,6 +7011,25 @@ sub process {
 			     "Prefer strscpy, strscpy_pad, or __nonstring over strncpy - see: https://github.com/KSPP/linux/issues/90\n" . $herecurr);
 		}
 
+# ethtool_sprintf uses that should likely be ethtool_puts
+		if ($line =~ /\bethtool_sprintf\s*\(\s*$FuncArg\s*,\s*$FuncArg\s*\)/) {
+			if (WARN("PREFER_ETHTOOL_PUTS",
+				 "Prefer ethtool_puts over ethtool_sprintf with only two arguments\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$fixlinenr] =~ s/\bethtool_sprintf\s*\(\s*($FuncArg)\s*,\s*($FuncArg)/ethtool_puts($1, $7)/;
+			}
+		}
+
+		# use $rawline because $line loses %s via sanitization and thus we can't match against it.
+		if ($rawline =~ /\bethtool_sprintf\s*\(\s*$FuncArg\s*,\s*\"\%s\"\s*,\s*$FuncArg\s*\)/) {
+			if (WARN("PREFER_ETHTOOL_PUTS",
+				 "Prefer ethtool_puts over ethtool_sprintf with standalone \"%s\" specifier\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$fixlinenr] =~ s/\bethtool_sprintf\s*\(\s*($FuncArg)\s*,\s*"\%s"\s*,\s*($FuncArg)/ethtool_puts($1, $7)/;
+			}
+		}
+
+
 # typecasts on min/max could be min_t/max_t
 		if ($perl_version_ok &&
 		    defined $stat &&