tests: Add focused unit test for device numbering

tests/xmlconfig.py

@@ -1035,19 +1035,16 @@ class TestXMLConfig(unittest.TestCase):
                           virtinst.DomainNumatune.cpuset_str_to_tuple,
                           conn, "16")
 
-    def testManyVirtio(self):
-        d = VirtualDisk(utils.get_conn())
-        d.bus = "virtio"
-        d.path = "/dev/default-pool/testvol1.img"
-
-        targetlist = []
-        for ignore in range(0, (26 * 2) + 1):
-            d.target = None
-            d.generate_target(targetlist)
-            targetlist.append(d.target)
-
-        self.assertEquals("vdaa", targetlist[26])
-        self.assertEquals("vdba", targetlist[26 * 2])
+    def testDiskNumbers(self):
+        self.assertEquals("a", VirtualDisk.num_to_target(1))
+        self.assertEquals("b", VirtualDisk.num_to_target(2))
+        self.assertEquals("z", VirtualDisk.num_to_target(26))
+        self.assertEquals("aa", VirtualDisk.num_to_target(27))
+        self.assertEquals("ab", VirtualDisk.num_to_target(28))
+        self.assertEquals("az", VirtualDisk.num_to_target(52))
+        self.assertEquals("ba", VirtualDisk.num_to_target(53))
+        self.assertEquals("zz", VirtualDisk.num_to_target(27 * 26))
+        self.assertEquals("aaa", VirtualDisk.num_to_target(27 * 26 + 1))
 
     def testFedoraTreeinfo(self):
         i = utils.make_distro_installer(

virtinst/devicedisk.py

@@ -395,6 +395,33 @@ class VirtualDisk(VirtualDevice):
     def build_vol_install(*args, **kwargs):
         return diskbackend.build_vol_install(*args, **kwargs)
 
+    @staticmethod
+    def num_to_target(num):
+        """
+        Convert an index in range (1, 1024) to a disk /dev number
+        (like hda, hdb, hdaa, etc.)
+        """
+        digits = []
+        for factor in range(0, 3):
+            amt = (num % (26 ** (factor + 1))) / (26 ** factor)
+            if amt == 0 and num >= (26 ** (factor + 1)):
+                amt = 26
+            num -= amt
+            digits.insert(0, amt)
+
+        seen_valid = False
+        gen_t = ""
+        for digit in digits:
+            if digit == 0:
+                if not seen_valid:
+                    continue
+                digit = 1
+
+            seen_valid = True
+            gen_t += "%c" % (ord('a') + digit - 1)
+
+        return gen_t
+
 
     _XML_PROP_ORDER = [
         "type", "device",
@@ -800,35 +827,9 @@ class VirtualDisk(VirtualDevice):
         @rtype C{str}
         """
         prefix, maxnode = self.get_target_prefix()
-        if prefix is None:
-            raise ValueError(_("Cannot determine device bus/type."))
 
-        if maxnode > (26 * 26 * 26):
-            raise RuntimeError("maxnode value is too high")
-
-        # Regular scanning
         for i in range(1, maxnode + 1):
-            gen_t = prefix
-
-            tmp = i
-            digits = []
-            for factor in range(0, 3):
-                amt = (tmp % (26 ** (factor + 1))) / (26 ** factor)
-                if amt == 0 and tmp >= (26 ** (factor + 1)):
-                    amt = 26
-                tmp -= amt
-                digits.insert(0, amt)
-
-            seen_valid = False
-            for digit in digits:
-                if digit == 0:
-                    if not seen_valid:
-                        continue
-                    digit = 1
-
-                seen_valid = True
-                gen_t += "%c" % (ord('a') + digit - 1)
-
+            gen_t = prefix + self.num_to_target(i)
             if gen_t not in skip_targets:
                 self.target = gen_t
                 return self.target