Test if the reparse point is a symlink

Introduce the caml/winsupport.h header to hold common code between the
runtime, lib-sys, and win32unix. This is also mandated by the name
conflict between ATOM from <windef.h> and caml/instruct.h.

Changes

@@ -87,8 +87,10 @@ Working version
   Allsopp, Nicolás Ojeda Bär, Vincent Laviron)
 
 - #10642: On Windows, Sys.remove and Unix.unlink now remove symlinks
-   to directories instead of raising EACCES. (Antonin Décimo, review
-   by David Allsopp, Xavier Leroy)
+  to directories instead of raising EACCES. Introduce
+  caml/winsupport.h to hold more common code between the runtime,
+  lib-sys, and win32unix. (Antonin Décimo, review by David Allsopp,
+  Xavier Leroy)
 
 ### Other libraries:
 

otherlibs/win32unix/readlink.c

@@ -23,6 +23,7 @@
 #include "unixsupport.h"
 #include <errno.h>
 #include <winioctl.h>
+#include <caml/winsupport.h>
 
 CAMLprim value unix_readlink(value opath)
 {

otherlibs/win32unix/stat.c

@@ -34,6 +34,7 @@
 #include <sys/stat.h>
 #include <time.h>
 #include <winioctl.h>
+#include "caml/winsupport.h"
 
 #ifndef S_IFLNK
 /*

otherlibs/win32unix/unixsupport.h

@@ -92,45 +92,6 @@ extern int win_set_inherit(HANDLE fd, BOOL inherit);
 }
 #endif
 
-/*
- * This structure is defined inconsistently. mingw64 has it in ntdef.h (which
- * doesn't look like a primary header) and technically it's part of ntifs.h in
- * the WDK. Requiring the WDK is a bit extreme, so the definition is taken from
- * ntdef.h. Both ntdef.h and ntifs.h define REPARSE_DATA_BUFFER_HEADER_SIZE
- */
-#ifndef REPARSE_DATA_BUFFER_HEADER_SIZE
-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;
-  };
-} REPARSE_DATA_BUFFER, *PREPARSE_DATA_BUFFER;
-#endif
-
 #define EXECV_CAST (const char_os * const *)
 
 #endif /* CAML_UNIXSUPPORT_H */

runtime/caml/winsupport.h

@@ -0,0 +1,65 @@
+/**************************************************************************/
+/*                                                                        */
+/*                                 OCaml                                  */
+/*                                                                        */
+/*                David Allsopp, MetaStack Solutions Ltd.                 */
+/*                                                                        */
+/*   Copyright 2015 MetaStack Solutions Ltd.                              */
+/*                                                                        */
+/*   All rights reserved.  This file is distributed under the terms of    */
+/*   the GNU Lesser General Public License version 2.1, with the          */
+/*   special exception on linking described in the file LICENSE.          */
+/*                                                                        */
+/**************************************************************************/
+
+/* Operating system - Windows specific stuff */
+
+#ifndef CAML_WINSUPPORT_H
+#define CAML_WINSUPPORT_H
+
+#if defined(_WIN32) && defined(CAML_INTERNALS)
+
+#include <windef.h>
+
+/*
+ * This structure is defined inconsistently. mingw64 has it in ntdef.h (which
+ * doesn't look like a primary header) and technically it's part of ntifs.h in
+ * the WDK. Requiring the WDK is a bit extreme, so the definition is taken from
+ * ntdef.h. Both ntdef.h and ntifs.h define REPARSE_DATA_BUFFER_HEADER_SIZE
+ */
+#ifndef REPARSE_DATA_BUFFER_HEADER_SIZE
+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;
+  };
+} REPARSE_DATA_BUFFER, *PREPARSE_DATA_BUFFER;
+#endif
+
+#endif
+
+#endif /* CAML_WINSUPPORT_H */

runtime/win32.c

@@ -26,6 +26,7 @@
 #include <wtypes.h>
 #include <winbase.h>
 #include <winsock2.h>
+#include <winioctl.h>
 #include <direct.h>
 #include <stdlib.h>
 #include <stdio.h>
@@ -47,6 +48,7 @@
 #include "caml/osdeps.h"
 #include "caml/signals.h"
 #include "caml/sys.h"
+#include "caml/winsupport.h"
 
 #include "caml/config.h"
 
@@ -799,24 +801,43 @@ int caml_win32_rename(const wchar_t * oldpath, const wchar_t * newpath)
 }
 
 int caml_win32_unlink(const wchar_t * path) {
-  int ret, attrs;
+  int ret;
 
   ret = _wunlink(path);
   /* On Windows, trying to unlink a symlink to a directory will return
    * EACCES, but the symlink can be deleted with rmdir. */
   if (ret == -1 && errno == EACCES) {
-    WIN32_FIND_DATAW data;
-    HANDLE h = FindFirstFileExW(path, FindExInfoStandard, &data,
-                                FindExSearchNameMatch, NULL, 0);
-    if (h != INVALID_HANDLE_VALUE &&
-        (data.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) &&
-        (data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) &&
-        data.dwReserved0 == IO_REPARSE_TAG_SYMLINK) {
-      FindClose(h);
-      ret = _wrmdir(path);
-      if (ret == -1)
-        errno = EACCES;
-    }
+    HANDLE h;
+    DWORD attrs, dummy;
+    union {
+      char buffer[16384];
+      REPARSE_DATA_BUFFER * point;
+    } buffer;
+
+    attrs = GetFileAttributes(path);
+    if (attrs == INVALID_FILE_ATTRIBUTES ||
+        !(attrs & (FILE_ATTRIBUTE_DIRECTORY | FILE_ATTRIBUTE_REPARSE_POINT)))
+      return -1;
+
+    h = CreateFile(path,
+                   FILE_READ_ATTRIBUTES,
+                   FILE_SHARE_DELETE | FILE_SHARE_READ | FILE_SHARE_WRITE,
+                   NULL,
+                   OPEN_EXISTING,
+                   FILE_FLAG_BACKUP_SEMANTICS | FILE_FLAG_OPEN_REPARSE_POINT,
+                   NULL);
+    if (h == INVALID_HANDLE_VALUE)
+      return -1;
+
+    ret = DeviceIoControl(h, FSCTL_GET_REPARSE_POINT, NULL, 0, &buffer.point,
+                          sizeof(buffer), &dummy, NULL);
+    CloseHandle(h);
+    if (!ret || buffer.point->ReparseTag != IO_REPARSE_TAG_SYMLINK)
+      return -1;
+
+    ret = _wrmdir(path);
+    if (ret == -1)
+      errno = EACCES;
   }
   return ret;
 }