Create Qcow2 class for reading Qcow2 and rebase it

Ref #466

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 <http://www.gnu.org/licenses/>.
+
+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()

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 <http://www.gnu.org/licenses/>.
+
+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")
+