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python - Python - Windows Raw Disk 无法读取最终扇区

问题描述

通过 Python 在 Windows 上访问原始磁盘时open()，无论出于何种原因，它都不允许我读取最后 10240 个字节（也就是 2048 个字节/扇区的最后 5 个扇区）。

当通过其他方式转储磁盘映像并比较图像时，我可以看到数据也不能假定为空。事实上，第一个缺失的扇区有一个 UDF 锚标记，其中包含相关元数据。以下扇区完全空白。

这就是我转储光盘内容的方式：

out = open("test.iso", "wb")
with open(r"\\.\D:", "rb") as f:
    while True:
        data = f.read(512)
        if len(data) == 0:
            break
        out.write(data)

如果我使用同一个 open() 对象并告诉它搜索到光盘的最后，它确实可以。因此，至少在搜索方面，它可以清楚地到达这些领域。如果我然后寻找 10240 字节然后尝试f.read(...)，它返回b''（空结果）而不是错误。我告诉它读什么大小也没关系。我尝试了各种大小，no-arg/default、1、12、255、512、2048、999999 等。

另一个 StackOverflow对不同（但相关）问题的回答也报告了关于增强音频光盘的类似发现，但此后似乎没有提出任何讨论。

我已经在来自不同类型工作室和创作者的多张 DVD 光盘上对此进行了测试，所有这些都处于良好状态，并且仍在发生。

示例重现代码：

import os
from wmi import WMI


DISC_LETTER = "D:"

c = WMI()
disc_info = next(iter(c.Win32_CDROMDrive(Drive=DISC_LETTER)), None)
if not disc_info:
    raise("Disc %s not found...", DISC_LETTER)

disc_size = int(disc_info.size)
disc_size += 10240  # WMIC also reports the size without 10240, but it is real!

f = open(r"\\.\%s" % DISC_LETTER, "rb")
f.seek(disc_size)
if f.tell() == disc_size:
    print("Seeked to the end of the disc...")
f.seek(-10240, os.SEEK_CUR)
if f.tell() == disc_size - (2048 * 5):
    print("Seeked 5 sectors before the end of the disc...")
data = f.read(2048 * 5):
print("Data read (len: %d): %b" % (len(data), data))

任何关于为什么这可能会很棒的想法，因为我已经尽我所能。

标签： pythonwindowswinapicd-romiso9660

解决方案

这似乎是在open(r'\\.\N:')打开具有受限边界的设备时发生的。

我的解决方案是使用 IOCTL 而不是 open() 打开光盘。特别是CreateFile、DeviceIoControl和FSCTL_ALLOW_EXTENDED_DASD_IO。

handle = win32file.CreateFile(
    r"\\.\D:",
    win32con.MAXIMUM_ALLOWED,
    win32con.FILE_SHARE_READ | win32con.FILE_SHARE_WRITE,
    None,
    win32con.OPEN_EXISTING,
    win32con.FILE_ATTRIBUTE_NORMAL,
    None
)
if handle == win32file.INVALID_HANDLE_VALUE:
    raise RuntimeError("Failed to obtain device handle...")
win32file.DeviceIoControl(handle, winioctlcon.FSCTL_ALLOW_EXTENDED_DASD_IO, None, None)

从这里我可以分别使用ReadFile和SetFilePointer作为 read 和 seek 的替代品。

我什至开发了一个新类，它可以加载所有内容并允许您动态读取和查找，而不必担心扇区对齐。

class Win32Device:
    """
    Class to read and seek a Windows Raw Device IO object without bother.
    It deals with getting the full size, allowing full access to all sectors,
    and alignment with the discs sector size.
    
    Author: PHOENiX <pragma.exe@gmail.com>
    License: Free, enjoy! This should be a thing open() does by default.
    """

    def __init__(self, target):
        # type: (str) -> None
        self.target = target
        self.sector_size = None
        self.disc_size = None
        self.position = 0

        self.handle = self.get_handle()
        self.geometry = self.get_geometry()

    def __enter__(self):
        return self

    def __exit__(self, *_, **__):
        self.dispose()

    def __len__(self) -> int:
        return self.geometry[-2]

    def dispose(self):
        if self.handle != win32file.INVALID_HANDLE_VALUE:
            win32file.CloseHandle(self.handle)

    def get_target(self):
        # type: () -> str
        """Get UNC target name. Can be `E:` or `PhysicalDriveN`."""
        target = self.target
        if not target.startswith("\\\\.\\"):
            target += rf"\\.\{target}"
        return target

    def get_handle(self):
        # type: () -> int
        """Get a direct handle to the raw UNC target, and unlock its IO capabilities."""
        handle = win32file.CreateFile(
            # https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
            self.get_target(),  # target
            win32con.MAXIMUM_ALLOWED,  # desired access
            win32con.FILE_SHARE_READ | win32con.FILE_SHARE_WRITE,  # share mode, write needed
            None,  # security attributes
            win32con.OPEN_EXISTING,  # creation disposition
            win32con.FILE_ATTRIBUTE_NORMAL,  # flags and attributes
            None  # template file
        )
        if handle == win32file.INVALID_HANDLE_VALUE:
            raise RuntimeError("Failed to obtain device handle...")
        # elevate accessible sectors, without this the last 5 sectors (in my case) will not be readable
        win32file.DeviceIoControl(handle, winioctlcon.FSCTL_ALLOW_EXTENDED_DASD_IO, None, None)
        return handle

    def get_geometry(self):
        # type: () -> tuple[int, ...]
        """
        Retrieves information about the physical disk's geometry.
        https://docs.microsoft.com/en-us/windows/win32/api/winioctl/ns-winioctl-disk_geometry_ex

        Returns a tuple of:
            Cylinders-Lo
            Cylinders-Hi
            Media Type
            Tracks Per Cylinder
            Sectors Per Track
            Bytes Per Sector
            Disk Size
            Extra Data
        """
        return struct.unpack("8L", win32file.DeviceIoControl(
            self.handle,  # handle
            winioctlcon.IOCTL_DISK_GET_DRIVE_GEOMETRY_EX,  # ioctl api
            b"",  # in buffer
            32  # out buffer
        ))

    def tell(self):
        # type: () -> int
        """Get current (spoofed) position."""
        return self.position

    def _tell(self):
        # type: () -> int
        """Get current real position."""
        if not self.handle:
            self.handle = self.get_handle()
        return win32file.SetFilePointer(self.handle, 0, win32file.FILE_CURRENT)

    def seek(self, offset, whence=os.SEEK_SET):
        # type: (int, int) -> int
        """Seek at any point in the stream, in an aligned way."""
        if whence == os.SEEK_CUR:
            whence = self.tell()
        elif whence == os.SEEK_END:
            whence = len(self)

        to = whence + offset
        closest = self.align(to)  # get as close as we can while being aligned

        if not self.handle:
            self.handle = self.get_handle()

        pos = win32file.SetFilePointer(self.handle, closest, win32file.FILE_BEGIN)
        if pos != closest:
            raise IOError(f"Seek was not precise...")

        self.position = to  # not actually at this location, read will deal with it
        return to

    def read(self, size=-1):
        # type: (int) -> Optional[bytes]
        """Read any amount of bytes in the stream, in an aligned way."""
        if not self.handle:
            self.handle = self.get_handle()

        sector_size = self.geometry[-3]
        offset = abs(self._tell() - self.tell())

        has_data = b''
        while self._tell() < self.tell() + size:
            res, data = win32file.ReadFile(self.handle, sector_size, None)
            if res != 0:
                raise IOError(f"An error occurred: {res} {data}")
            if len(data) < sector_size:
                raise IOError(f"Read {sector_size - len(data)} less bytes than requested...")
            has_data += data
        # seek to the position wanted + size read, which will then be re-aligned
        self.seek(self.tell() + size)

        return has_data[offset:offset + size]

    def align(self, size, to=None):
        # type: (int, Optional[int]) -> int
        """
        Align size to the closest but floor mod `to` value.
        Examples:
            align(513, to=512)
            >>>512
            align(1023, to=512)
            >>>512
            align(1026, to=512)
            >>>1024
            align(12, to=10)
            >>>10
        """
        if not to:
            to = self.geometry[-3]  # logical bytes per sector value
        return math.floor(size / to) * to

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