[ros-kernel] Registry links demystfied

[Eric K. <ek...@rz...>]

Hi!

One of the most mysterious details of the registry has been uncovered, the
registry link. Didn't you ever wonder what this REG_LINK value type is used
for? Or what about the key access right KEY_CREATE_LINK?

At least one registry link is used in Windows NT/2K/XP.
"HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet" is a link to one of the
"HKEY_LOCAL_MACHINE\SYSTEM\ControlSetXXX" keys (XXX can be any three digit
number, starting at 001).

The available documentation does not provide any useful information about
registry links other than trivial statements, like: 'A registry link is a
link to link registry keys.'

On the net, I found a posting about someones unsuccessful attempt to create
a registry link. This was the only useful information I found.

After some extensive research I got it working:
Let's assume you have a existing key "HKEY_LOCAL_MACHINE\SOFTWARE\SMT" and
the new key "HKEY_LOCAL_MACHINE\SOFTWARE\Test\Link" should point to it. Then
the following code will do the trick:

HKEY hKeyHandle;
DWORD dwDisposition;
DWORD dwLength;

PWCHAR ValueName = L"SymbolicLinkValue";
PWCHAR Buffer= L"\\Registry\\Machine\\SOFTWARE\\SMT";

/* create the key */
RegCreateKeyExW(HKEY_LOCAL_MACHINE,
      L"SOFTWARE\\Test\\Link",
      0,
      NULL,
      REG_OPTION_VOLATILE | REG_OPTION_CREATE_LINK,
      KEY_ALL_ACCESS | KEY_CREATE_LINK,
      NULL,
      &hKeyHandle,
      &dwDisposition);

/* Note: length WITHOUT the terminating zero */
dwLength = wcslen(Buffer) * sizeof(WCHAR);

/* set the link value */
RegSetValueExW(hKeyHandle,
     ValueName,
     0,
     REG_LINK,
     (const BYTE *)Buffer,
     dwLength);

RegCloseKey(hKeyHandle);


I still have to find out whether registry links can be removed or changed.


Regards,
Eric