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106 lines
3.3 KiB
106 lines
3.3 KiB
#!/usr/bin/env python
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#
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# Copyright (C) 2016 GNS3 Technologies Inc.
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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import os
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import asyncio
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import struct
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class Qcow2Error(Exception):
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pass
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class Qcow2:
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"""
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Allows to parse a Qcow2 file
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"""
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def __init__(self, path):
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self._path = path
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self._reload()
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def _reload(self):
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# Each QCOW2 file begins with a header, in big endian format, as follows:
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#
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# typedef struct QCowHeader {
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# uint32_t magic;
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# uint32_t version;
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#
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# uint64_t backing_file_offset;
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# uint32_t backing_file_size;
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#
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# uint32_t cluster_bits;
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# uint64_t size; /* in bytes */
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# uint32_t crypt_method;
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#
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# uint32_t l1_size;
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# uint64_t l1_table_offset;
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#
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# uint64_t refcount_table_offset;
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# uint32_t refcount_table_clusters;
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#
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# uint32_t nb_snapshots;
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# uint64_t snapshots_offset;
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# } QCowHeader;
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struct_format = ">IIQi"
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with open(self._path, 'rb') as f:
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content = f.read(struct.calcsize(struct_format))
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try:
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self.magic, self.version, self.backing_file_offset, self.backing_file_size = struct.unpack_from(struct_format, content)
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except struct.error:
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raise Qcow2Error("Invalid file header for {}".format(self._path))
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if self.magic != 1363560955: # The first 4 bytes contain the characters 'Q', 'F', 'I' followed by 0xfb.
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raise Qcow2Error("Invalid magic for {}".format(self._path))
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@property
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def backing_file(self):
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"""
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When using linked clone this will return the path to the base image
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:returns: None if it's not a linked clone, the path otherwise
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"""
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with open(self._path, 'rb') as f:
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f.seek(self.backing_file_offset)
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content = f.read(self.backing_file_size)
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path = content.decode()
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if len(path) == 0:
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return None
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return path
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async def rebase(self, qemu_img, base_image):
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"""
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Rebase a linked clone in order to use the correct disk
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:param qemu_img: Path to the qemu-img binary
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:param base_image: Path to the base image
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"""
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if not os.path.exists(base_image):
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raise FileNotFoundError(base_image)
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command = [qemu_img, "rebase", "-u", "-b", base_image, self._path]
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process = await asyncio.create_subprocess_exec(*command)
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retcode = await process.wait()
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if retcode != 0:
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raise Qcow2Error("Could not rebase the image")
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self._reload()
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