How to get the target folder of a link?

Question

How to get the target folder of a link?

Heiko 1,291

Within my app I let the user open file system directories in explorer. But if I have e.g. a directory

C:\Users\Heiko\Documents\Eigene Bilder\

C:\Users\Heiko\Documents\My Pictures\

and try to open it via

Process.Start(@"C:\Users\Heiko\Documents\Eigene Bilder");

the explorer opens and displays the message 'Cannot open the folder. Access is forbidden.'. Of course the folder is a link to folder 'C:\Users\Heiko\Pictures' and here I have all rights to do something.

How can I get the target path for such folders? I only need the path for opening it via explorer.

Until now I have the following in C#:

WIN32_FIND_DATA wfd = new WIN32_FIND_DATA();

using (SafeFindHandle fh = FindFirstFile(Path.Combine(path, "*"), wfd))
{
	if (fh.IsInvalid)
		continue;

	do
	{
		if ((wfd.dwFileAttributes & FileAttributes.Directory) == FileAttributes.Directory)
		{
			if (wfd.cFileName == "." || wfd.cFileName == "..")
				continue;

			if ((wfd.dwFileAttributes & FileAttributes.ReparsePoint) == FileAttributes.ReparsePoint &&
				(wfd.dwReparseTags == IO_REPARSE_TAG_MOUNT_POINT || wfd.dwReparseTags == IO_REPARSE_TAG_SYMLINK))
			{
				// How to get here the target folder?
			}
		}
		//...
	} while (FindNextFile(fh, wfd));
}

Heiko 1,291 Reputation points

2023-02-13T12:44:12.6366667+00:00

Thank you, it works, if I can get the directory handle.

Accepted answer

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Your answer

Heiko 1,291 Reputation points

2023-02-13T12:44:12.6366667+00:00

Thank you, it works, if I can get the directory handle.

Answer 1

David Lowndes 4,721

Have you had a look at using the GetFinalPathNameByHandle API?

David Lowndes 4,721

Alternatively, if you were using modern C++, you could do:

    if ( std::filesystem::is_symlink( dirName ) )
    {
        auto rs = std::filesystem::read_symlink( dirName );
        auto TargetName = rs.c_str();

Which (delving into the implementation), eventually uses this in MS's current implementation:

    if (DeviceIoControl(reinterpret_cast<HANDLE>(_Handle), FSCTL_GET_REPARSE_POINT, nullptr, 0, _Buffer, _Buffer_size,
            &_Bytes_returned, nullptr)) {

Heiko 1,291 Reputation points

2023-02-13T14:04:57.6033333+00:00

Thank you, but I use CreateFileW() and GetFinalPathNameByHandleW() because it is simpler to use it in C#.
RLWA32 47,616 Reputation points

2023-02-13T14:46:34.05+00:00

Of the three ways to obtain the target of a reparse point (GetFinalPathNameByHandle, DeviceIOControl and IShellLink2) in my opinion DeviceIOControl is the most resilient.

IShellLink2 succeeds with symlinks but fails with mounted folders.

GetFinalPathNameByHandle fails if the target of a symlink or mounted folder is not available (e.g., disk is not mounted or is offline).

DeviceIOControl succeeds in all cases by opening the reparse point and returning the relevant contents.
Heiko 1,291 Reputation points

2023-02-13T15:48:37.0166667+00:00
Thank you for the information. But if I call the following:

HANDLE hDir = CreateFileW(L"C:\\Users\\Heiko\\Documents\\Eigene Bilder", 0, 0, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL); if (hDir != INVALID_HANDLE_VALUE) { wchar_t path[MAX_PATH]; DWORD len; BOOL ret = DeviceIoControl(hDir, FSCTL_GET_REPARSE_POINT, NULL, 0, path, sizeof(path), &len, NULL); if (!ret) len = GetLastError(); CloseHandle(hDir); }

GetLastError() returns 0x00001126 (ERROR_NOT_A_REPARSE_POINT).

Based on your explanation, GetFinalPathNameByHandleW() is a good choice. It works for the path and if the target is not there, then it is ok for the app logic that it does not return a target.
RLWA32 47,616 Reputation points

2023-02-13T16:06:45.8166667+00:00

When using CreateFile to open a reparse point and return a handle for DeviceIOControl you must also pass FILE_FLAG_OPEN_REPARSE_POINT
Heiko 1,291 Reputation points

2023-02-13T16:32:45.24+00:00

Thanx, then I get a header of 16 bytes, so I would need a structure for that, but as I said, I use GetFinalPathNameByHandleW() now.

I found https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/ns-ntifs-_reparse_data_buffer?redirectedfrom=MSDN

Answer 2

Hello,

Welcome to Microsoft Q&A!

As the answer said, you can use PKEY_Link_TargetParsingPath to retrieve the target path.

Or you can use CreateFile to open the target file and then retrieve the path name.

HANDLE h =CreateFile(L"C:\\Users\\SymbolicLink\\To\\MyFolder", GENERIC_READ, FILE_SHARE_READ,NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS,NULL);

Thank you.

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Answer 3

Heiko 1,291

Thank you, but If I try to get the directory handle by

HANDLE hFile = CreateFileW(L"C:\\Users\\Heiko\\Documents\\Eigene Bilder", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);

I always get 0xFFFFFFFF and last error is 5 (Access denied).

I figured out, that the following works:

HANDLE hFile = CreateFileW(L"C:\\Users\\Heiko\\Documents\\Eigene Bilder", 0, 0, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);

Then I can get the linked path with GetFinalPathNameByHandleW().

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How to get the target folder of a link?

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