qcow2.py: move qcow2 format classes to separate module

We are going to enhance qcow2 format parsing by adding more structure
classes. Let's split format parsing from utility code.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20200606081806.23897-4-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 173 insertions, 0 deletions

diff --git a/tests/qemu-iotests/qcow2_format.py b/tests/qemu-iotests/qcow2_format.py
new file mode 100644
index 0000000000..0e517c1bbc
--- /dev/null
+++ b/tests/qemu-iotests/qcow2_format.py
@@ -0,0 +1,173 @@
+# Library for manipulations with qcow2 image
+#
+# 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/>.
+#
+
+import struct
+import string
+
+
+class QcowHeaderExtension:
+
+    def __init__(self, magic, length, data):
+        if length % 8 != 0:
+            padding = 8 - (length % 8)
+            data += b"\0" * padding
+
+        self.magic = magic
+        self.length = length
+        self.data = data
+
+    @classmethod
+    def create(cls, magic, data):
+        return QcowHeaderExtension(magic, len(data), data)
+
+
+class QcowHeader:
+
+    uint32_t = 'I'
+    uint64_t = 'Q'
+
+    fields = [
+        # Version 2 header fields
+        [uint32_t, '%#x',  'magic'],
+        [uint32_t, '%d',   'version'],
+        [uint64_t, '%#x',  'backing_file_offset'],
+        [uint32_t, '%#x',  'backing_file_size'],
+        [uint32_t, '%d',   'cluster_bits'],
+        [uint64_t, '%d',   'size'],
+        [uint32_t, '%d',   'crypt_method'],
+        [uint32_t, '%d',   'l1_size'],
+        [uint64_t, '%#x',  'l1_table_offset'],
+        [uint64_t, '%#x',  'refcount_table_offset'],
+        [uint32_t, '%d',   'refcount_table_clusters'],
+        [uint32_t, '%d',   'nb_snapshots'],
+        [uint64_t, '%#x',  'snapshot_offset'],
+
+        # Version 3 header fields
+        [uint64_t, 'mask', 'incompatible_features'],
+        [uint64_t, 'mask', 'compatible_features'],
+        [uint64_t, 'mask', 'autoclear_features'],
+        [uint32_t, '%d',   'refcount_order'],
+        [uint32_t, '%d',   'header_length'],
+    ]
+
+    fmt = '>' + ''.join(field[0] for field in fields)
+
+    def __init__(self, fd):
+
+        buf_size = struct.calcsize(QcowHeader.fmt)
+
+        fd.seek(0)
+        buf = fd.read(buf_size)
+
+        header = struct.unpack(QcowHeader.fmt, buf)
+        self.__dict__ = dict((field[2], header[i])
+                             for i, field in enumerate(QcowHeader.fields))
+
+        self.set_defaults()
+        self.cluster_size = 1 << self.cluster_bits
+
+        fd.seek(self.header_length)
+        self.load_extensions(fd)
+
+        if self.backing_file_offset:
+            fd.seek(self.backing_file_offset)
+            self.backing_file = fd.read(self.backing_file_size)
+        else:
+            self.backing_file = None
+
+    def set_defaults(self):
+        if self.version == 2:
+            self.incompatible_features = 0
+            self.compatible_features = 0
+            self.autoclear_features = 0
+            self.refcount_order = 4
+            self.header_length = 72
+
+    def load_extensions(self, fd):
+        self.extensions = []
+
+        if self.backing_file_offset != 0:
+            end = min(self.cluster_size, self.backing_file_offset)
+        else:
+            end = self.cluster_size
+
+        while fd.tell() < end:
+            (magic, length) = struct.unpack('>II', fd.read(8))
+            if magic == 0:
+                break
+            else:
+                padded = (length + 7) & ~7
+                data = fd.read(padded)
+                self.extensions.append(QcowHeaderExtension(magic, length,
+                                                           data))
+
+    def update_extensions(self, fd):
+
+        fd.seek(self.header_length)
+        extensions = self.extensions
+        extensions.append(QcowHeaderExtension(0, 0, b""))
+        for ex in extensions:
+            buf = struct.pack('>II', ex.magic, ex.length)
+            fd.write(buf)
+            fd.write(ex.data)
+
+        if self.backing_file is not None:
+            self.backing_file_offset = fd.tell()
+            fd.write(self.backing_file)
+
+        if fd.tell() > self.cluster_size:
+            raise Exception("I think I just broke the image...")
+
+    def update(self, fd):
+        header_bytes = self.header_length
+
+        self.update_extensions(fd)
+
+        fd.seek(0)
+        header = tuple(self.__dict__[f] for t, p, f in QcowHeader.fields)
+        buf = struct.pack(QcowHeader.fmt, *header)
+        buf = buf[0:header_bytes-1]
+        fd.write(buf)
+
+    def dump(self):
+        for f in QcowHeader.fields:
+            value = self.__dict__[f[2]]
+            if f[1] == 'mask':
+                bits = []
+                for bit in range(64):
+                    if value & (1 << bit):
+                        bits.append(bit)
+                value_str = str(bits)
+            else:
+                value_str = f[1] % value
+
+            print("%-25s" % f[2], value_str)
+        print("")
+
+    def dump_extensions(self):
+        for ex in self.extensions:
+
+            data = ex.data[:ex.length]
+            if all(c in string.printable.encode('ascii') for c in data):
+                data = "'%s'" % data.decode('ascii')
+            else:
+                data = "<binary>"
+
+            print("Header extension:")
+            print("%-25s %#x" % ("magic", ex.magic))
+            print("%-25s %d" % ("length", ex.length))
+            print("%-25s %s" % ("data", data))
+            print("")