diff --git a/tests/qemu-iotests/257 b/tests/qemu-iotests/257
index 2933e2670b..adf4cdfe6e 100755
--- a/tests/qemu-iotests/257
+++ b/tests/qemu-iotests/257
@@ -24,120 +24,12 @@ import os
 
 import iotests
 from iotests import log, qemu_img
+from bitmaps import EmulatedBitmap, GROUPS
 
 SIZE = 64 * 1024 * 1024
 GRANULARITY = 64 * 1024
 
 
-class Pattern:
-    def __init__(self, byte, offset, size=GRANULARITY):
-        self.byte = byte
-        self.offset = offset
-        self.size = size
-
-    def bits(self, granularity):
-        lower = self.offset // granularity
-        upper = (self.offset + self.size - 1) // granularity
-        return set(range(lower, upper + 1))
-
-
-class PatternGroup:
-    """Grouping of Pattern objects. Initialize with an iterable of Patterns."""
-    def __init__(self, patterns):
-        self.patterns = patterns
-
-    def bits(self, granularity):
-        """Calculate the unique bits dirtied by this pattern grouping"""
-        res = set()
-        for pattern in self.patterns:
-            res |= pattern.bits(granularity)
-        return res
-
-
-GROUPS = [
-    PatternGroup([
-        # Batch 0: 4 clusters
-        Pattern('0x49', 0x0000000),
-        Pattern('0x6c', 0x0100000),   # 1M
-        Pattern('0x6f', 0x2000000),   # 32M
-        Pattern('0x76', 0x3ff0000)]), # 64M - 64K
-    PatternGroup([
-        # Batch 1: 6 clusters (3 new)
-        Pattern('0x65', 0x0000000),   # Full overwrite
-        Pattern('0x77', 0x00f8000),   # Partial-left (1M-32K)
-        Pattern('0x72', 0x2008000),   # Partial-right (32M+32K)
-        Pattern('0x69', 0x3fe0000)]), # Adjacent-left (64M - 128K)
-    PatternGroup([
-        # Batch 2: 7 clusters (3 new)
-        Pattern('0x74', 0x0010000),   # Adjacent-right
-        Pattern('0x69', 0x00e8000),   # Partial-left  (1M-96K)
-        Pattern('0x6e', 0x2018000),   # Partial-right (32M+96K)
-        Pattern('0x67', 0x3fe0000,
-                2*GRANULARITY)]),     # Overwrite [(64M-128K)-64M)
-    PatternGroup([
-        # Batch 3: 8 clusters (5 new)
-        # Carefully chosen such that nothing re-dirties the one cluster
-        # that copies out successfully before failure in Group #1.
-        Pattern('0xaa', 0x0010000,
-                3*GRANULARITY),       # Overwrite and 2x Adjacent-right
-        Pattern('0xbb', 0x00d8000),   # Partial-left (1M-160K)
-        Pattern('0xcc', 0x2028000),   # Partial-right (32M+160K)
-        Pattern('0xdd', 0x3fc0000)]), # New; leaving a gap to the right
-]
-
-
-class EmulatedBitmap:
-    def __init__(self, granularity=GRANULARITY):
-        self._bits = set()
-        self.granularity = granularity
-
-    def dirty_bits(self, bits):
-        self._bits |= set(bits)
-
-    def dirty_group(self, n):
-        self.dirty_bits(GROUPS[n].bits(self.granularity))
-
-    def clear(self):
-        self._bits = set()
-
-    def clear_bits(self, bits):
-        self._bits -= set(bits)
-
-    def clear_bit(self, bit):
-        self.clear_bits({bit})
-
-    def clear_group(self, n):
-        self.clear_bits(GROUPS[n].bits(self.granularity))
-
-    @property
-    def first_bit(self):
-        return sorted(self.bits)[0]
-
-    @property
-    def bits(self):
-        return self._bits
-
-    @property
-    def count(self):
-        return len(self.bits)
-
-    def compare(self, qmp_bitmap):
-        """
-        Print a nice human-readable message checking that a bitmap as reported
-        by the QMP interface has as many bits set as we expect it to.
-        """
-
-        name = qmp_bitmap.get('name', '(anonymous)')
-        log("= Checking Bitmap {:s} =".format(name))
-
-        want = self.count
-        have = qmp_bitmap['count'] // qmp_bitmap['granularity']
-
-        log("expecting {:d} dirty sectors; have {:d}. {:s}".format(
-            want, have, "OK!" if want == have else "ERROR!"))
-        log('')
-
-
 class Drive:
     """Represents, vaguely, a drive attached to a VM.
     Includes format, graph, and device information."""
diff --git a/tests/qemu-iotests/bitmaps.py b/tests/qemu-iotests/bitmaps.py
new file mode 100644
index 0000000000..522fc25171
--- /dev/null
+++ b/tests/qemu-iotests/bitmaps.py
@@ -0,0 +1,131 @@
+# Bitmap-related helper utilities
+#
+# Copyright (c) 2020 John Snow for Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# owner=jsnow@redhat.com
+
+from iotests import log
+
+GRANULARITY = 64 * 1024
+
+
+class Pattern:
+    def __init__(self, byte, offset, size=GRANULARITY):
+        self.byte = byte
+        self.offset = offset
+        self.size = size
+
+    def bits(self, granularity):
+        lower = self.offset // granularity
+        upper = (self.offset + self.size - 1) // granularity
+        return set(range(lower, upper + 1))
+
+
+class PatternGroup:
+    """Grouping of Pattern objects. Initialize with an iterable of Patterns."""
+    def __init__(self, patterns):
+        self.patterns = patterns
+
+    def bits(self, granularity):
+        """Calculate the unique bits dirtied by this pattern grouping"""
+        res = set()
+        for pattern in self.patterns:
+            res |= pattern.bits(granularity)
+        return res
+
+
+GROUPS = [
+    PatternGroup([
+        # Batch 0: 4 clusters
+        Pattern('0x49', 0x0000000),
+        Pattern('0x6c', 0x0100000),   # 1M
+        Pattern('0x6f', 0x2000000),   # 32M
+        Pattern('0x76', 0x3ff0000)]), # 64M - 64K
+    PatternGroup([
+        # Batch 1: 6 clusters (3 new)
+        Pattern('0x65', 0x0000000),   # Full overwrite
+        Pattern('0x77', 0x00f8000),   # Partial-left (1M-32K)
+        Pattern('0x72', 0x2008000),   # Partial-right (32M+32K)
+        Pattern('0x69', 0x3fe0000)]), # Adjacent-left (64M - 128K)
+    PatternGroup([
+        # Batch 2: 7 clusters (3 new)
+        Pattern('0x74', 0x0010000),   # Adjacent-right
+        Pattern('0x69', 0x00e8000),   # Partial-left  (1M-96K)
+        Pattern('0x6e', 0x2018000),   # Partial-right (32M+96K)
+        Pattern('0x67', 0x3fe0000,
+                2*GRANULARITY)]),     # Overwrite [(64M-128K)-64M)
+    PatternGroup([
+        # Batch 3: 8 clusters (5 new)
+        # Carefully chosen such that nothing re-dirties the one cluster
+        # that copies out successfully before failure in Group #1.
+        Pattern('0xaa', 0x0010000,
+                3*GRANULARITY),       # Overwrite and 2x Adjacent-right
+        Pattern('0xbb', 0x00d8000),   # Partial-left (1M-160K)
+        Pattern('0xcc', 0x2028000),   # Partial-right (32M+160K)
+        Pattern('0xdd', 0x3fc0000)]), # New; leaving a gap to the right
+]
+
+
+class EmulatedBitmap:
+    def __init__(self, granularity=GRANULARITY):
+        self._bits = set()
+        self.granularity = granularity
+
+    def dirty_bits(self, bits):
+        self._bits |= set(bits)
+
+    def dirty_group(self, n):
+        self.dirty_bits(GROUPS[n].bits(self.granularity))
+
+    def clear(self):
+        self._bits = set()
+
+    def clear_bits(self, bits):
+        self._bits -= set(bits)
+
+    def clear_bit(self, bit):
+        self.clear_bits({bit})
+
+    def clear_group(self, n):
+        self.clear_bits(GROUPS[n].bits(self.granularity))
+
+    @property
+    def first_bit(self):
+        return sorted(self.bits)[0]
+
+    @property
+    def bits(self):
+        return self._bits
+
+    @property
+    def count(self):
+        return len(self.bits)
+
+    def compare(self, qmp_bitmap):
+        """
+        Print a nice human-readable message checking that a bitmap as reported
+        by the QMP interface has as many bits set as we expect it to.
+        """
+
+        name = qmp_bitmap.get('name', '(anonymous)')
+        log("= Checking Bitmap {:s} =".format(name))
+
+        want = self.count
+        have = qmp_bitmap['count'] // qmp_bitmap['granularity']
+
+        log("expecting {:d} dirty sectors; have {:d}. {:s}".format(
+            want, have, "OK!" if want == have else "ERROR!"))
+        log('')
