bitbake/fetch: Spell out which fetcher backends support and recommend checksums

index f629c01..9864595 100644
@@ -271,10 +271,13 @@ def verify_checksum(u, ud, d):
     matched
     """
 
+    if not ud.method.supports_checksum(ud):
+        return
+
     md5data = bb.utils.md5_file(ud.localpath)
     sha256data = bb.utils.sha256_file(ud.localpath)
 
-    if ud.type in ["http", "https", "ftp", "ftps"]:
+    if ud.method.recommends_checksum(ud):
         # If strict checking enabled and neither sum defined, raise error
         strict = d.getVar("BB_STRICT_CHECKSUM", True) or None
         if (strict and ud.md5_expected == None and ud.sha256_expected == None):

@@ -578,10 +581,14 @@ class FetchData(object):
             self.sha256_name = "sha256sum"
         if self.md5_name in self.parm:
             self.md5_expected = self.parm[self.md5_name]
+        elif self.type not in ["http", "https", "ftp", "ftps"]:
+            self.md5_expected = None
         else:
             self.md5_expected = d.getVarFlag("SRC_URI", self.md5_name)
         if self.sha256_name in self.parm:
             self.sha256_expected = self.parm[self.sha256_name]
+        elif self.type not in ["http", "https", "ftp", "ftps"]:
+            self.sha256_expected = None
         else:
             self.sha256_expected = d.getVarFlag("SRC_URI", self.sha256_name)
 

@@ -660,6 +667,19 @@ class FetchMethod(object):
         """
         return os.path.join(data.getVar("DL_DIR", d, True), urldata.localfile)
 
+    def supports_checksum(self, urldata):
+        """
+        Is localpath something that can be represented by a checksum?
+        """
+        return True
+
+    def recommends_checksum(self, urldata):
+        """
+        Is the backend on where checksumming is recommended (should warnings 
+        by displayed if there is no checksum)?
+        """
+        return False
+
     def _strip_leading_slashes(self, relpath):
         """
         Remove leading slash as os.path.join can't cope

index 962cc0a..ecc5e0d 100644
@@ -82,6 +82,9 @@ class Git(FetchMethod):
         """
         return ud.type in ['git']
 
+    def supports_checksum(self, urldata):
+        return False
+
     def urldata_init(self, ud, d):
         """
         init git specific variable within url data

index 91ac15f..8d6434a 100644
@@ -69,6 +69,9 @@ class SSH(FetchMethod):
     def supports(self, url, urldata, d):
         return __pattern__.match(url) != None
 
+    def supports_checksum(self, urldata):
+        return False
+
     def localpath(self, url, urldata, d):
         m = __pattern__.match(urldata.url)
         path = m.group('path')

index 98900ac..e223b21 100644
@@ -45,6 +45,9 @@ class Wget(FetchMethod):
         """
         return ud.type in ['http', 'https', 'ftp']
 
+    def recommends_checksum(self, urldata):
+        return True
+
     def urldata_init(self, ud, d):
 
         ud.basename = os.path.basename(ud.path)