diff --git a/gns3server/modules/qemu/qcow2.py b/gns3server/modules/qemu/qcow2.py
new file mode 100644
index 00000000..9f0fc462
--- /dev/null
+++ b/gns3server/modules/qemu/qcow2.py
@@ -0,0 +1,100 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2016 GNS3 Technologies 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 3 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 .
+
+import os
+import asyncio
+import struct
+
+
+class Qcow2Error(Exception):
+ pass
+
+
+class Qcow2:
+ """
+ Allow to parse a Qcow2 file
+ """
+
+ def __init__(self, path):
+
+ self.path = path
+ self._reload()
+
+ def _reload(self):
+ # Each QCOW2 file begins with a header, in big endian format, as follows:
+ #
+ # typedef struct QCowHeader {
+ # uint32_t magic;
+ # uint32_t version;
+ #
+ # uint64_t backing_file_offset;
+ # uint32_t backing_file_size;
+ #
+ # uint32_t cluster_bits;
+ # uint64_t size; /* in bytes */
+ # uint32_t crypt_method;
+ #
+ # uint32_t l1_size;
+ # uint64_t l1_table_offset;
+ #
+ # uint64_t refcount_table_offset;
+ # uint32_t refcount_table_clusters;
+ #
+ # uint32_t nb_snapshots;
+ # uint64_t snapshots_offset;
+ # } QCowHeader;
+ struct_format = ">IIQi"
+
+ with open(self.path, 'rb') as f:
+ content = f.read(struct.calcsize(struct_format))
+
+ self.magic, self.version, self.backing_file_offset, self.backing_file_size = struct.unpack_from(struct_format, content)
+
+ if self.magic != 1363560955: # The first 4 bytes contain the characters 'Q', 'F', 'I' followed by 0xfb.
+ raise Qcow2Error("Invalid magic for {}".format(self.path))
+
+ @property
+ def backing_file(self):
+ """
+ When using linked clone this will return the path to the base image
+
+ :returns: None if it's not a linked clone, the path otherwise
+ """
+ with open(self.path, 'rb') as f:
+ f.seek(self.backing_file_offset)
+ content = f.read(self.backing_file_size)
+ path = content.decode()
+ if len(path) == 0:
+ return None
+ return path
+
+ @asyncio.coroutine
+ def rebase(self, qemu_img, base_image):
+ """
+ Rebase a linked clone in order to use the correct disk
+
+ :param qemu_img: Path to the qemu-img binary
+ :param base_image: Path to the base image
+ """
+ if not os.path.exists(base_image):
+ raise FileNotFoundError(base_image)
+ command = [qemu_img, "rebase", "-u", "-b", base_image, self.path]
+ process = yield from asyncio.create_subprocess_exec(*command)
+ retcode = yield from process.wait()
+ if retcode != 0:
+ raise Qcow2Error("Could not rebase the image")
+ self._reload()
diff --git a/tests/modules/qemu/test_qcow2.py b/tests/modules/qemu/test_qcow2.py
new file mode 100644
index 00000000..d193c625
--- /dev/null
+++ b/tests/modules/qemu/test_qcow2.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2016 GNS3 Technologies 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 3 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 .
+
+import os
+import pytest
+import shutil
+import asyncio
+
+from gns3server.modules.qemu.qcow2 import Qcow2,Qcow2Error
+
+
+def qemu_img():
+ """
+ Return the path of qemu-img on system.
+ We can't use shutil.which because for safety reason we break
+ the PATH to avoid test interacting with real binaries
+ """
+ paths = [
+ "/usr/bin/qemu-img",
+ "/usr/local/bin/qemu-img"
+ ]
+ for path in paths:
+ if os.path.exists(path):
+ return path
+ return None
+
+
+def test_valid_base_file():
+ qcow2 = Qcow2("tests/resources/empty8G.qcow2")
+ assert qcow2.version == 3
+ assert qcow2.backing_file is None
+
+
+def test_valid_linked_file():
+ qcow2 = Qcow2("tests/resources/linked.qcow2")
+ assert qcow2.version == 3
+ assert qcow2.backing_file == "empty8G.qcow2"
+
+
+def test_invalid_file():
+ with pytest.raises(Qcow2Error):
+ Qcow2("tests/resources/nvram_iou")
+
+
+@pytest.mark.skipif(qemu_img() is None, reason="qemu-img is not available")
+def test_rebase(tmpdir, loop):
+ shutil.copy("tests/resources/empty8G.qcow2", str(tmpdir / "empty16G.qcow2"))
+ shutil.copy("tests/resources/linked.qcow2", str(tmpdir / "linked.qcow2"))
+ qcow2 = Qcow2(str(tmpdir / "linked.qcow2"))
+ assert qcow2.version == 3
+ assert qcow2.backing_file == "empty8G.qcow2"
+ loop.run_until_complete(asyncio.async(qcow2.rebase(qemu_img(), str(tmpdir / "empty16G.qcow2"))))
+ assert qcow2.backing_file == str(tmpdir / "empty16G.qcow2")
+
diff --git a/tests/resources/empty8G.qcow2 b/tests/resources/empty8G.qcow2
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diff --git a/tests/resources/linked.qcow2 b/tests/resources/linked.qcow2
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index 00000000..8fad5487
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