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Re: [PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initializat
From: |
Vladimir Sementsov-Ogievskiy |
Subject: |
Re: [PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initialization method |
Date: |
Thu, 16 Jul 2020 11:47:17 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 |
14.07.2020 00:36, Andrey Shinkevich wrote:
There are two ways to initialize a class derived from Qcow2Struct:
1. Pass a block of binary data to the constructor.
2. Pass the file descriptor to allow reading the file from constructor.
Let's change the Qcow2BitmapExt initialization method from 1 to 2 to
support a scattered reading in the initialization chain.
The implementation comes with the patch that follows.
Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Andrey Shinkevich <andrey.shinkevich@virtuozzo.com>
---
tests/qemu-iotests/qcow2_format.py | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)
diff --git a/tests/qemu-iotests/qcow2_format.py
b/tests/qemu-iotests/qcow2_format.py
index 2f3681b..cbaffc4 100644
--- a/tests/qemu-iotests/qcow2_format.py
+++ b/tests/qemu-iotests/qcow2_format.py
@@ -113,6 +113,11 @@ class Qcow2BitmapExt(Qcow2Struct):
('u64', '{:#x}', 'bitmap_directory_offset')
)
+ def __init__(self, fd):
+ super().__init__(fd=fd)
+ pad = (struct.calcsize(self.fmt) + 7) & ~7
It's a size of structure rounded up to 8-bytes boundary. But after super init,
we should alread be at the end of the structure and need to add only padding,
not the whole structure rounded up. I think, correct code should be:
tail = struct.calcsize(self.fmt) % 8
if tail:
fd.seek(8 - tail, 1)
+ if pad:
+ fd.seek(pad, 1)
QCOW2_EXT_MAGIC_BITMAPS = 0x23852875
@@ -161,21 +166,21 @@ class QcowHeaderExtension(Qcow2Struct):
else:
Hmm, you parse data now only for this "else:" branch. Prior to this patch, it was parsed for
"if fd is None:" branch as well, after the whole "if" statement. This is wrong.
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
-
- data_str = self.data[:self.length]
- if all(c in string.printable.encode('ascii') for c in data_str):
- data_str = f"'{ data_str.decode('ascii') }'"
- else:
- data_str = '<binary>'
- self.data_str = data_str
+ if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
+ self.obj = Qcow2BitmapExt(fd=fd)
+ else:
+ padded = (self.length + 7) & ~7
+ self.data = fd.read(padded)
+ assert self.data is not None
+ self.obj = None
+ data_str = self.data[:self.length]
+ if all(c in string.printable.encode(
+ 'ascii') for c in data_str):
+ data_str = f"'{ data_str.decode('ascii') }'"
+ else:
+ data_str = '<binary>'
+ self.data_str = data_str
- if self.magic == QCOW2_EXT_MAGIC_BITMAPS:
- self.obj = Qcow2BitmapExt(data=self.data)
- else:
- self.obj = None
def dump(self):
super().dump()
--
Best regards,
Vladimir
- Re: [PATCH v10 09/10] qcow2_format.py: collect fields to dump in JSON format, (continued)
[PATCH v10 04/10] qcow2_format.py: dump bitmap flags in human readable way., Andrey Shinkevich, 2020/07/13
[PATCH v10 06/10] qcow2_format.py: pass cluster size to substructures, Andrey Shinkevich, 2020/07/13
[PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initialization method, Andrey Shinkevich, 2020/07/13
- Re: [PATCH v10 03/10] qcow2_format.py: change Qcow2BitmapExt initialization method,
Vladimir Sementsov-Ogievskiy <=
[PATCH v10 10/10] qcow2_format.py: support dumping metadata in JSON format, Andrey Shinkevich, 2020/07/13
[PATCH v10 08/10] qcow2.py: Introduce '-j' key to dump in JSON format, Andrey Shinkevich, 2020/07/13
[PATCH v10 07/10] qcow2_format.py: Dump bitmap table serialized entries, Andrey Shinkevich, 2020/07/13