=== modified file 'preupgrade/__init__.py'
--- preupgrade/__init__.py	2008-11-14 17:03:17 +0000
+++ preupgrade/__init__.py	2008-11-17 16:44:44 +0000
@@ -31,6 +31,7 @@
 import yum, rpm
 import yum.Errors
 import rpmUtils.arch
+from yum.misc import checksum
 
 from yum.parser import varReplace
 from yum.constants import *
@@ -265,6 +266,7 @@
         # FIXME what happens if the network isn't up yet?
         self.release_map = self.retrieve_release_info(configfile)
         self.bootpath='/boot/upgrade'
+        self.image_csums = {} # filename = (csumtype, csum)
         # Noisy if these plugins don't exist, but doesn't raise an exception
         self._getConfig(enabled_plugins=['blacklist','whiteout'])
         if release:
@@ -461,7 +463,12 @@
                 self.mainimage = 'images/stage2.img'
         except ConfigParser.NoOptionError, e:
             raise PUError, "Invalid treeinfo: %s" % str(e)
-
+        
+        if cp.has_section('checksums'):
+            for opt_fn in cp.options('checksums'):
+                (csum_type, csum) = cp.get('checksums', opt_fn).split(':')
+                self.image_csums[opt_fn] = (csum_type, csum)
+ 
         tif.close()
         
     
@@ -489,13 +496,19 @@
 
         # see if we have it and if it is the right size        
         if os.path.exists(local):
-            local_stat = os.stat(local)
-            if int(local_stat.st_size) == int(mysize):
-                # File exists and it's the right size.. guess it's probably OK
-                # TODO: we have sha1sums in .treeinfo now - check 'em!
-                return True
+            if self.image_csums.has_key(fileinfo):
+                csumtype, csum = self.image_csums[fileinfo]:
+                if csum == checksum(csumtype, local):
+                    return True
+                else:
+                    os.unlink(local)
             else:
-                os.unlink(local)
+                local_stat = os.stat(local)
+                if int(local_stat.st_size) == int(mysize):
+                    # File exists and it's the right size.. guess it's probably OK
+                    return True
+                else:
+                    os.unlink(local)
 
         # if we are this far we're going to try to download it
         # check for available disk space
@@ -509,7 +522,13 @@
         except URLGrabError, e:
             os.unlink(local)
             raise PUError, "failure downloading %s: %s" % (item_fname, e)
-            
+
+        if self.image_csums.has_key(fileinfo):
+            csumtype, csum = self.image_csums[fileinfo]:
+            if csum != checksum(csumtype, local):
+                os.unlink(local)
+                raise PUError, "failure downloading %s: %s" % (item_fname, e)
+
         return True
 
     def remove_boot_files(self):