Commit a9e750e1 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Eric Blake
Browse files

qcow2_format: refactor QcowHeaderExtension as a subclass of Qcow2Struct 



Only two fields we can parse by generic code, but that is better than
nothing. Keep further refactoring of variable-length fields for another
day.

Signed-off-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: default avatarAndrey Shinkevich <andrey.shinkevich@virtuozzo.com>
Message-Id: <20200606081806.23897-12-vsementsov@virtuozzo.com>
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
parent 0931fcc7

tests/qemu-iotests/qcow2_format.py

+37 −16
Original line number Diff line number Diff line
@@ -97,16 +97,41 @@ class Qcow2Struct(metaclass=Qcow2StructMeta): 
            print('{:<25} {}'.format(f[2], value_str))





class QcowHeaderExtension:

class QcowHeaderExtension(Qcow2Struct):



    def __init__(self, magic, length, data):

        if length % 8 != 0:

            padding = 8 - (length % 8)

            data += b'\0' * padding

    fields = (

        ('u32', '{:#x}', 'magic'),

        ('u32', '{}', 'length')

        # length bytes of data follows

        # then padding to next multiply of 8

    )



    def __init__(self, magic=None, length=None, data=None, fd=None):

        """

        Support both loading from fd and creation from user data.

        For fd-based creation current position in a file will be used to read

        the data.



        This should be somehow refactored and functionality should be moved to

        superclass (to allow creation of any qcow2 struct), but then, fields

        of variable length (data here) should be supported in base class

        somehow. So, it's a TODO. We'll see how to properly refactor this when

        we have more qcow2 structures.

        """

        if fd is None:

            assert all(v is not None for v in (magic, length, data))

            self.magic = magic

            self.length = length

            if length % 8 != 0:

                padding = 8 - (length % 8)

                data += b'\0' * padding

            self.data = data

        else:

            assert all(v is None for v in (magic, length, data))

            super().__init__(fd=fd)

            padded = (self.length + 7) & ~7

            self.data = fd.read(padded)

            assert self.data is not None



    def dump(self):

        data = self.data[:self.length]
@@ -115,8 +140,7 @@ class QcowHeaderExtension: 
        else:

            data = '<binary>'



        print(f'{"magic":<25} {self.magic:#x}')

        print(f'{"length":<25} {self.length}')

        super().dump()

        print(f'{"data":<25} {data}')



    @classmethod
@@ -182,14 +206,11 @@ class QcowHeader(Qcow2Struct): 
            end = self.cluster_size



        while fd.tell() < end:

            (magic, length) = struct.unpack('>II', fd.read(8))

            if magic == 0:

            ext = QcowHeaderExtension(fd=fd)

            if ext.magic == 0:

                break

            else:

                padded = (length + 7) & ~7

                data = fd.read(padded)

                self.extensions.append(QcowHeaderExtension(magic, length,

                                                           data))

                self.extensions.append(ext)



    def update_extensions(self, fd):