C or C++ API to explore the tree of mounts

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  DriveInfo.GetDrives Method

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  George Frias - AWWshop @ Wikidot, Wiki1978

  Sunday, February 2, 2020 2:37 AM
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  Environment.SpecialFolder Enum

  ShellSpecialFolderConstants enumeration
  
  

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  George Frias - AWWshop @ Wikidot, Wiki1978

  Sunday, February 2, 2020 2:42 AM
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  I'd try asking for help over here.

  https://social.msdn.microsoft.com/Forums/vstudio/en-US/home?forum=vcgeneral

  https://social.msdn.microsoft.com/Forums/vstudio/en-US/home?forum=csharpgeneral

  https://social.msdn.microsoft.com/Forums/windowsdesktop/en-us/home?forum=windowsgeneraldevelopmentissues

   

   

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  Regards, Dave Patrick ....
  Microsoft Certified Professional
  Microsoft MVP [Windows Server] Datacenter Management
  
  Disclaimer: This posting is provided "AS IS" with no warranties or guarantees, and confers no rights.
  

  
  

  • Edited by Dave PatrickMVP Sunday, February 2, 2020 5:02 AM
  • Proposed as answer by Richard MuellerMVP, Banned Sunday, February 2, 2020 1:34 PM
  • Marked as answer by Cacadril2 Monday, February 3, 2020 12:40 AM

  Sunday, February 2, 2020 4:49 AM
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  Hello,

  Below is the exact question that I would like to ask. What forum would be appropriate?

  I want to write a C or C++ program to create a list of all mounts on a computer. I use a known mounted folder to check that the function calls work as I expect from the documentation. 

  Using FindFirstFile I observe that "C:\Documents and Settings" has FILE_ATTRIBUTE_REPARSE_POINT set in WIN32_FIND_DATA.dwFileAttributes and WIN32_FIND_DATA.dwReserved0 (which should countain the reparse tag) equals IO_REPARSE_TAG_MOUNT_POINT.
  
  So I think that C:\Documents and Settings is a mounted folder. I know that it points to C:\Users. But how can I determine this in a C program?

  I have tried GetVolumeNameForMountPointW and FindFirstVolumeMountPoint, as per the web page "Enumerating Mounted Folders", but I get INVALID_HANDLE_VALUE returned from FindFirstVolumeMountPoint.

  Thanks

  ---

  Enrique Perez-Terron

  A junction for a mounted folder is not the same as a junction for a mounted volume.

  Chances are that a call to GetLastError will return 5 (Access denied) when FindFirstVolumeMountPoint fails.  if you enumerate volume mount points in a process with elevated privileges (running as an Administrator) the enumeration will likely not fail with an access denied error.  However, since "C:\Documents and Settings" is NOT a mounted volume it will not be returned in the enumeration.

  The following sample code will retrieve the target mounted folder or mounted volume. 

  #include <Windows.h>
  #include <stdio.h>
  
  typedef struct _REPARSE_DATA_BUFFER {
  	ULONG  ReparseTag;
  	USHORT ReparseDataLength;
  	USHORT Reserved;
  	union {
  		struct {
  			USHORT SubstituteNameOffset;
  			USHORT SubstituteNameLength;
  			USHORT PrintNameOffset;
  			USHORT PrintNameLength;
  			ULONG  Flags;
  			WCHAR  PathBuffer[1];
  		} SymbolicLinkReparseBuffer;
  		struct {
  			USHORT SubstituteNameOffset;
  			USHORT SubstituteNameLength;
  			USHORT PrintNameOffset;
  			USHORT PrintNameLength;
  			WCHAR  PathBuffer[1];
  		} MountPointReparseBuffer;
  		struct {
  			UCHAR DataBuffer[1];
  		} GenericReparseBuffer;
  	} DUMMYUNIONNAME;
  } REPARSE_DATA_BUFFER, *PREPARSE_DATA_BUFFER;
  
  int wmain()
  {
  	WCHAR szDirectory[] = L"C:\\Documents and Settings";
  
  	DWORD attributes = GetFileAttributesW(szDirectory);
  	if (attributes != INVALID_FILE_ATTRIBUTES)
  	{
  		if ((attributes & FILE_ATTRIBUTE_REPARSE_POINT) != 0)
  		{
  			WIN32_FIND_DATAW wfd;
  
  			HANDLE hFind = FindFirstFileW(szDirectory, &wfd);
  			if (hFind != INVALID_HANDLE_VALUE)
  			{
  				if ((wfd.dwReserved0 & IO_REPARSE_TAG_SYMLINK) == IO_REPARSE_TAG_SYMLINK)
  					wprintf_s(L"%s is a symlink\n", szDirectory);
  				else if ((wfd.dwReserved0 & IO_REPARSE_TAG_MOUNT_POINT) == IO_REPARSE_TAG_MOUNT_POINT)
  					wprintf_s(L"%s is a mounted folder\n", szDirectory);
  
  				FindClose(hFind);
  			}
  
  			HANDLE hDir = CreateFileW(szDirectory, 0, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT, NULL);
  			if (hDir != INVALID_HANDLE_VALUE)
  			{
  				DWORD bytes = 0;
  				UINT bufsize = sizeof(REPARSE_DATA_BUFFER) + 128;
  				PREPARSE_DATA_BUFFER prdb = (PREPARSE_DATA_BUFFER)malloc(bufsize);
  				while (TRUE)
  				{
  					if (!DeviceIoControl(hDir, FSCTL_GET_REPARSE_POINT, NULL, 0, prdb, bufsize, &bytes, NULL))
  					{
  						DWORD err = GetLastError();
  						if (err == ERROR_INSUFFICIENT_BUFFER || err == ERROR_MORE_DATA)
  						{
  							bufsize *= 2;
  							prdb = (PREPARSE_DATA_BUFFER)realloc(prdb, bufsize);
  						}
  						else
  						{
  							wprintf_s(L"DeviceIoControl error code was %d\n", err);
  							break;
  						}
  					}
  					else
  					{
  						if (prdb->ReparseTag == IO_REPARSE_TAG_MOUNT_POINT)
  						{
  							wprintf_s(L"Mounted Folder path is %.*s\n",
  								prdb->MountPointReparseBuffer.PrintNameLength / sizeof(WCHAR),
  								&prdb->MountPointReparseBuffer.PathBuffer[prdb->MountPointReparseBuffer.PrintNameOffset / sizeof(WCHAR)]);
  						}
  						else if (prdb->ReparseTag == IO_REPARSE_TAG_SYMLINK)
  						{
  							wprintf_s(L"Symlink target is %.*s\n",
  								prdb->SymbolicLinkReparseBuffer.PrintNameLength / sizeof(WCHAR),
  								&prdb->SymbolicLinkReparseBuffer.PathBuffer[prdb->SymbolicLinkReparseBuffer.PrintNameOffset / sizeof(WCHAR)]);
  						}
  
  						break;
  					}
  				}
  
  				free(prdb);
  			}
  			else
  				wprintf_s(L"CreateFile error was %d\n", GetLastError());
  		}
  		else
  			wprintf_s(L"%s is not a reparse point\n", szDirectory);
  	}
  	else
  		wprintf_s(L"GetFileAttributes error was %d\n", GetLastError());
  
  
  
  	return 0;
  }
  

  
  

  • Marked as answer by Cacadril2 Monday, February 3, 2020 12:44 AM

  Sunday, February 2, 2020 4:45 PM