使用struct作为Python ctypes模块的函数参数

Question

我正在尝试把我之前为Windows编写的一个处理连接点/符号链接等的Python C扩展，转换成纯Python代码，使用ctypes模块。不过，由于我之前对ctypes的使用经验比较有限，我觉得我可能在某个地方犯了错误，导致我的代码运行不正常。到目前为止，我的代码是这样的：

from os import path
from ctypes import *
from ctypes.wintypes import *

# Python implementation of:
#
# typedef struct {
#       DWORD   ReparseTag;
#       DWORD   ReparseDataLength;
#       WORD    Reserved;
#       WORD    ReparseTargetLength;
#       WORD    ReparseTargetMaximumLength;
#       WORD    Reserved1;
#       WCHAR   ReparseTarget[1];
# } REPARSE_MOUNTPOINT_DATA_BUFFER, *PREPARSE_MOUNTPOINT_DATA_BUFFER;

class ReparsePoint(Structure):
    _fields_ = [
        ("ReparseTag", DWORD),
        ("ReparseDataLength", DWORD),
        ("Reserved", WORD),

        ("ReparseTargetLength", WORD),
        ("ReparseTargetMaximumLength", WORD),
        ("Reserved1", WORD),
        ("ReparseTarget", c_wchar_p),
    ]

GENERIC_READ = 0x80000000
GENERIC_WRITE = 0x40000000

FILE_SHARE_DELETE = 0x00000004
FILE_SHARE_READ = 0x00000001
FILE_SHARE_WRITE = 0x00000002
FILE_SHARE_READ_WRITE = (FILE_SHARE_READ | FILE_SHARE_WRITE)

OPEN_EXISTING = 3

IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003
REPARSE_MOUNTPOINT_HEADER_SIZE = 8

FSCTL_SET_REPARSE_POINT = 589988
FILE_FLAG_OPEN_REPARSE_POINT = 2097152
FILE_FLAG_BACKUP_SEMANTICS = 33554432
FILE_FLAG_REPARSE_BACKUP = 35651584 # FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS

INVALID_HANDLE_VALUE = -1
LPOVERLAPPED = c_void_p
LPSECURITY_ATTRIBUTES = c_void_p

NULL = 0
FALSE = BOOL(0)
TRUE = BOOL(1)

def CreateFile(filename, access, sharemode, creation, flags):
    return HANDLE(windll.kernel32.CreateFileW(
        LPWSTR(filename),
        DWORD(access),
        DWORD(sharemode),
        LPSECURITY_ATTRIBUTES(NULL),
        DWORD(creation),
        DWORD(flags),
        HANDLE(NULL)
    ))

def CreateDirectory(fpath):
    return windll.kernel32.CreateDirectoryW(LPWSTR(fpath), LPSECURITY_ATTRIBUTES(NULL)) != FALSE

def RemoveDirectory(fpath):
    return windll.kernel32.RemoveDirectoryW(LPWSTR(fpath)) != FALSE

def translate_path(fpath):
    fpath = path.abspath(fpath)
    if fpath[len(fpath)-1] == '\\' and fpath[len(fpath)-2] == ':':
        fpath = fpath[:len(fpath)-1]
    return '\\??\\%s' % fpath

def junction(source, link_name):
    """ Create a junction at link_name pointing to source directory. """
    if not path.isdir(source):
        raise Exception('Junction source does not exist or is not a directory.')

    link_name = path.abspath(link_name)
    if path.exists(link_name):
        raise Exception('Filepath for new junction already exists.')

    if not CreateDirectory(link_name):
        raise Exception('Failed to create new directory for target junction.')

    source = translate_path(source)
    hFile = CreateFile(link_name, GENERIC_WRITE, 0, OPEN_EXISTING, FILE_FLAG_REPARSE_BACKUP)
    if hFile == HANDLE(INVALID_HANDLE_VALUE):
        raise Exception('Failed to open directory for junction creation.')

    datalen = len(source) * sizeof(c_wchar)
    reparseInfo = ReparsePoint(
        IO_REPARSE_TAG_MOUNT_POINT,
        datalen + 12,
        0,
        datalen,
        datalen + sizeof(c_wchar),
        0,
        source
    )
    pReparseInfo = pointer(reparseInfo)

    print reparseInfo.ReparseTarget
    returnedLength = DWORD(0)
    result = BOOL(
        windll.kernel32.DeviceIoControl(
            hFile,
            DWORD(FSCTL_SET_REPARSE_POINT),
            pReparseInfo,
            DWORD(reparseInfo.ReparseDataLength + REPARSE_MOUNTPOINT_HEADER_SIZE),
            LPVOID(NULL),
            DWORD(0),
            byref(returnedLength),
            LPOVERLAPPED(NULL)
        )
    ) == TRUE

    #if not result:
        #RemoveDirectory(link_name)

    windll.kernel32.CloseHandle(hFile)
    return result

print junction('G:\\cpp.workspace\\tools', 'test')
"""
Just putting this here for the moment so I know how to call the function.   

BOOL WINAPI DeviceIoControl(
  __in         HANDLE hDevice,
  __in         DWORD dwIoControlCode,
  __in_opt     LPVOID lpInBuffer,
  __in         DWORD nInBufferSize,
  __out_opt    LPVOID lpOutBuffer,
  __in         DWORD nOutBufferSize,
  __out_opt    LPDWORD lpBytesReturned,
  __inout_opt  LPOVERLAPPED lpOverlapped
);
"""

现在运行这段代码时，它会为目标连接点创建一个文件夹（在这个例子中是test）。它似乎还在给这个文件夹加上一个重新解析标签，告诉系统这个文件夹是一个连接点。但是，连接点并没有指向"G:\cpp.workspace\tools"（或者说是\??\G:\cpp.workspace\tools），而是指向了：㢨\獬。

显然，这个问题出在reparseInfo.ReparseTarget上，但我一直没能搞清楚我哪里做错了。

符号链接文件系统 windows ctypes c扩展 struct 连接点重新解析标签

使用struct作为Python ctypes模块的函数参数

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