src/port/dirmod.c - cloudberry - Git at Google

 /*-------------------------------------------------------------------------
  *
  * dirmod.c
  *	  directory handling functions
  *
  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  *	This includes replacement versions of functions that work on
  *	Windows.
  *
  * IDENTIFICATION
  *	  src/port/dirmod.c
  *
  *-------------------------------------------------------------------------
  */

 #ifndef FRONTEND
 #include "postgres.h"
 #else
 #include "postgres_fe.h"
 #endif

 /* Don't modify declarations in system headers */
 #if defined(WIN32) || defined(__CYGWIN__)
 #undef rename
 #undef unlink
 #endif

 #include <unistd.h>
 #include <sys/stat.h>

 #if defined(WIN32) || defined(__CYGWIN__)
 #ifndef __CYGWIN__
 #include <winioctl.h>
 #else
 #include <windows.h>
 #include <w32api/winioctl.h>
 #endif
 #endif

 #if defined(WIN32) && !defined(__CYGWIN__)
 #include "port/win32ntdll.h"
 #endif

 #if defined(WIN32) || defined(__CYGWIN__)

 /*
  *	pgrename
  */
 int
 pgrename(const char *from, const char *to)
 {
 	int			loops = 0;

 	/*
 	 * We need to loop because even though PostgreSQL uses flags that allow
 	 * rename while the file is open, other applications might have the file
 	 * open without those flags.  However, we won't wait indefinitely for
 	 * someone else to close the file, as the caller might be holding locks
 	 * and blocking other backends.
 	 */
 #if defined(WIN32) && !defined(__CYGWIN__)
 	while (!MoveFileEx(from, to, MOVEFILE_REPLACE_EXISTING))
 #else
 	while (rename(from, to) < 0)
 #endif
 	{
 #if defined(WIN32) && !defined(__CYGWIN__)
 		DWORD		err = GetLastError();

 		_dosmaperr(err);

 		/*
 		 * Modern NT-based Windows versions return ERROR_SHARING_VIOLATION if
 		 * another process has the file open without FILE_SHARE_DELETE.
 		 * ERROR_LOCK_VIOLATION has also been seen with some anti-virus
 		 * software. This used to check for just ERROR_ACCESS_DENIED, so
 		 * presumably you can get that too with some OS versions. We don't
 		 * expect real permission errors where we currently use rename().
 		 */
 		if (err != ERROR_ACCESS_DENIED &&
 			err != ERROR_SHARING_VIOLATION &&
 			err != ERROR_LOCK_VIOLATION)
 			return -1;
 #else
 		if (errno != EACCES)
 			return -1;
 #endif

 		if (++loops > 100)		/* time out after 10 sec */
 			return -1;
 		pg_usleep(100000);		/* us */
 	}
 	return 0;
 }

 /*
  * Check if _pglstat64()'s reason for failure was STATUS_DELETE_PENDING.
  * This doesn't apply to Cygwin, which has its own lstat() that would report
  * the case as EACCES.
 */
 static bool
 lstat_error_was_status_delete_pending(void)
 {
 	if (errno != ENOENT)
 		return false;
 #if defined(WIN32) && !defined(__CYGWIN__)
 	if (pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
 		return true;
 #endif
 	return false;
 }

 /*
  *	pgunlink
  */
 int
 pgunlink(const char *path)
 {
 	bool		is_lnk;
 	int			loops = 0;
 	struct stat st;

 	/*
 	 * This function might be called for a regular file or for a junction
 	 * point (which we use to emulate symlinks).  The latter must be unlinked
 	 * with rmdir() on Windows.  Before we worry about any of that, let's see
 	 * if we can unlink directly, since that's expected to be the most common
 	 * case.
 	 */
 	if (unlink(path) == 0)
 		return 0;
 	if (errno != EACCES)
 		return -1;

 	/*
 	 * EACCES is reported for many reasons including unlink() of a junction
 	 * point.  Check if that's the case so we can redirect to rmdir().
 	 *
 	 * Note that by checking only once, we can't cope with a path that changes
 	 * from regular file to junction point underneath us while we're retrying
 	 * due to sharing violations, but that seems unlikely.  We could perhaps
 	 * prevent that by holding a file handle ourselves across the lstat() and
 	 * the retry loop, but that seems like over-engineering for now.
 	 *
 	 * In the special case of a STATUS_DELETE_PENDING error (file already
 	 * unlinked, but someone still has it open), we don't want to report
 	 * ENOENT to the caller immediately, because rmdir(parent) would probably
 	 * fail. We want to wait until the file truly goes away so that simple
 	 * recursive directory unlink algorithms work.
 	 */
 	if (lstat(path, &st) < 0)
 	{
 		if (lstat_error_was_status_delete_pending())
 			is_lnk = false;
 		else
 			return -1;
 	}
 	else
 		is_lnk = S_ISLNK(st.st_mode);

 	/*
 	 * We need to loop because even though PostgreSQL uses flags that allow
 	 * unlink while the file is open, other applications might have the file
 	 * open without those flags.  However, we won't wait indefinitely for
 	 * someone else to close the file, as the caller might be holding locks
 	 * and blocking other backends.
 	 */
 	while ((is_lnk ? rmdir(path) : unlink(path)) < 0)
 	{
 		if (errno != EACCES)
 			return -1;
 		if (++loops > 100)		/* time out after 10 sec */
 			return -1;
 		pg_usleep(100000);		/* us */
 	}
 	return 0;
 }

 /* We undefined these above; now redefine for possible use below */
 #define rename(from, to)		pgrename(from, to)
 #define unlink(path)			pgunlink(path)
 #endif							/* defined(WIN32) || defined(__CYGWIN__) */


 #if defined(WIN32) && !defined(__CYGWIN__)	/* Cygwin has its own symlinks */

 /*
  *	pgsymlink support:
  *
  *	This struct is a replacement for REPARSE_DATA_BUFFER which is defined in VC6 winnt.h
  *	but omitted in later SDK functions.
  *	We only need the SymbolicLinkReparseBuffer part of the original struct's union.
  */
 typedef struct
 {
 	DWORD		ReparseTag;
 	WORD		ReparseDataLength;
 	WORD		Reserved;
 	/* SymbolicLinkReparseBuffer */
 	WORD		SubstituteNameOffset;
 	WORD		SubstituteNameLength;
 	WORD		PrintNameOffset;
 	WORD		PrintNameLength;
 	WCHAR		PathBuffer[FLEXIBLE_ARRAY_MEMBER];
 } REPARSE_JUNCTION_DATA_BUFFER;

 #define REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE   \
 		FIELD_OFFSET(REPARSE_JUNCTION_DATA_BUFFER, SubstituteNameOffset)


 /*
  *	pgsymlink - uses Win32 junction points
  *
  *	For reference:	http://www.codeproject.com/KB/winsdk/junctionpoints.aspx
  */
 int
 pgsymlink(const char *oldpath, const char *newpath)
 {
 	HANDLE		dirhandle;
 	DWORD		len;
 	char		buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
 	char		nativeTarget[MAX_PATH];
 	char	   *p = nativeTarget;
 	REPARSE_JUNCTION_DATA_BUFFER *reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER *) buffer;

 	CreateDirectory(newpath, 0);
 	dirhandle = CreateFile(newpath, GENERIC_READ | GENERIC_WRITE,
 						   0, 0, OPEN_EXISTING,
 						   FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS, 0);

 	if (dirhandle == INVALID_HANDLE_VALUE)
 	{
 		_dosmaperr(GetLastError());
 		return -1;
 	}

 	/* make sure we have an unparsed native win32 path */
 	if (memcmp("\\??\\", oldpath, 4) != 0)
 		snprintf(nativeTarget, sizeof(nativeTarget), "\\??\\%s", oldpath);
 	else
 		strlcpy(nativeTarget, oldpath, sizeof(nativeTarget));

 	while ((p = strchr(p, '/')) != NULL)
 		*p++ = '\\';

 	len = strlen(nativeTarget) * sizeof(WCHAR);
 	reparseBuf->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
 	reparseBuf->ReparseDataLength = len + 12;
 	reparseBuf->Reserved = 0;
 	reparseBuf->SubstituteNameOffset = 0;
 	reparseBuf->SubstituteNameLength = len;
 	reparseBuf->PrintNameOffset = len + sizeof(WCHAR);
 	reparseBuf->PrintNameLength = 0;
 	MultiByteToWideChar(CP_ACP, 0, nativeTarget, -1,
 						reparseBuf->PathBuffer, MAX_PATH);

 	/*
 	 * FSCTL_SET_REPARSE_POINT is coded differently depending on SDK version;
 	 * we use our own definition
 	 */
 	if (!DeviceIoControl(dirhandle,
 						 CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 41, METHOD_BUFFERED, FILE_ANY_ACCESS),
 						 reparseBuf,
 						 reparseBuf->ReparseDataLength + REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE,
 						 0, 0, &len, 0))
 	{
 		LPSTR		msg;
 		int			save_errno;

 		_dosmaperr(GetLastError());
 		save_errno = errno;

 		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
 					  FORMAT_MESSAGE_IGNORE_INSERTS |
 					  FORMAT_MESSAGE_FROM_SYSTEM,
 					  NULL, GetLastError(),
 					  MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
 					  (LPSTR) &msg, 0, NULL);
 #ifndef FRONTEND
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not set junction for \"%s\": %s",
 						nativeTarget, msg)));
 #else
 		fprintf(stderr, _("could not set junction for \"%s\": %s\n"),
 				nativeTarget, msg);
 #endif
 		LocalFree(msg);

 		CloseHandle(dirhandle);
 		RemoveDirectory(newpath);

 		errno = save_errno;

 		return -1;
 	}

 	CloseHandle(dirhandle);

 	return 0;
 }

 /*
  *	pgreadlink - uses Win32 junction points
  */
 int
 pgreadlink(const char *path, char *buf, size_t size)
 {
 	DWORD		attr;
 	HANDLE		h;
 	char		buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
 	REPARSE_JUNCTION_DATA_BUFFER *reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER *) buffer;
 	DWORD		len;
 	int			r;

 	attr = GetFileAttributes(path);
 	if (attr == INVALID_FILE_ATTRIBUTES)
 	{
 		_dosmaperr(GetLastError());
 		return -1;
 	}
 	if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == 0)
 	{
 		errno = EINVAL;
 		return -1;
 	}

 	h = CreateFile(path,
 				   GENERIC_READ,
 				   FILE_SHARE_READ | FILE_SHARE_WRITE,
 				   NULL,
 				   OPEN_EXISTING,
 				   FILE_FLAG_OPEN_REPARSE_POINT | FILE_FLAG_BACKUP_SEMANTICS,
 				   0);
 	if (h == INVALID_HANDLE_VALUE)
 	{
 		_dosmaperr(GetLastError());
 		return -1;
 	}

 	if (!DeviceIoControl(h,
 						 FSCTL_GET_REPARSE_POINT,
 						 NULL,
 						 0,
 						 (LPVOID) reparseBuf,
 						 sizeof(buffer),
 						 &len,
 						 NULL))
 	{
 		LPSTR		msg;

 		errno = 0;
 		FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
 					  FORMAT_MESSAGE_IGNORE_INSERTS |
 					  FORMAT_MESSAGE_FROM_SYSTEM,
 					  NULL, GetLastError(),
 					  MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
 					  (LPSTR) &msg, 0, NULL);
 #ifndef FRONTEND
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not get junction for \"%s\": %s",
 						path, msg)));
 #else
 		fprintf(stderr, _("could not get junction for \"%s\": %s\n"),
 				path, msg);
 #endif
 		LocalFree(msg);
 		CloseHandle(h);
 		errno = EINVAL;
 		return -1;
 	}
 	CloseHandle(h);

 	/* Got it, let's get some results from this */
 	if (reparseBuf->ReparseTag != IO_REPARSE_TAG_MOUNT_POINT)
 	{
 		errno = EINVAL;
 		return -1;
 	}

 	r = WideCharToMultiByte(CP_ACP, 0,
 							reparseBuf->PathBuffer, -1,
 							buf,
 							size,
 							NULL, NULL);

 	if (r <= 0)
 	{
 		errno = EINVAL;
 		return -1;
 	}

 	/* r includes the null terminator */
 	r -= 1;

 	/*
 	 * If the path starts with "\??\" followed by a "drive absolute" path
 	 * (known to Windows APIs as RtlPathTypeDriveAbsolute), then strip that
 	 * prefix.  This undoes some of the transformation performed by
 	 * pgsymlink(), to get back to a format that users are used to seeing.  We
 	 * don't know how to transform other path types that might be encountered
 	 * outside PGDATA, so we just return them directly.
 	 */
 	if (r >= 7 &&
 		buf[0] == '\\' &&
 		buf[1] == '?' &&
 		buf[2] == '?' &&
 		buf[3] == '\\' &&
 		isalpha(buf[4]) &&
 		buf[5] == ':' &&
 		buf[6] == '\\')
 	{
 		memmove(buf, buf + 4, strlen(buf + 4) + 1);
 		r -= 4;
 	}
 	return r;
 }

 #endif							/* defined(WIN32) && !defined(__CYGWIN__) */
	/*-------------------------------------------------------------------------
	*
	* dirmod.c
	* directory handling functions
	*
	* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
	* Portions Copyright (c) 1994, Regents of the University of California
	*
	* This includes replacement versions of functions that work on
	* Windows.
	*
	* IDENTIFICATION
	* src/port/dirmod.c
	*
	*-------------------------------------------------------------------------
	*/

	#ifndef FRONTEND
	#include "postgres.h"
	#else
	#include "postgres_fe.h"
	#endif

	/* Don't modify declarations in system headers */
	#if defined(WIN32) \|\| defined(__CYGWIN__)
	#undef rename
	#undef unlink
	#endif

	#include <unistd.h>
	#include <sys/stat.h>

	#if defined(WIN32) \|\| defined(__CYGWIN__)
	#ifndef __CYGWIN__
	#include <winioctl.h>
	#else
	#include <windows.h>
	#include <w32api/winioctl.h>
	#endif
	#endif

	#if defined(WIN32) && !defined(__CYGWIN__)
	#include "port/win32ntdll.h"
	#endif

	#if defined(WIN32) \|\| defined(__CYGWIN__)

	/*
	* pgrename
	*/
	int
	pgrename(const char from, const char to)
	{
	int loops = 0;

	/*
	* We need to loop because even though PostgreSQL uses flags that allow
	* rename while the file is open, other applications might have the file
	* open without those flags. However, we won't wait indefinitely for
	* someone else to close the file, as the caller might be holding locks
	* and blocking other backends.
	*/
	#if defined(WIN32) && !defined(__CYGWIN__)
	while (!MoveFileEx(from, to, MOVEFILE_REPLACE_EXISTING))
	#else
	while (rename(from, to) < 0)
	#endif
	{
	#if defined(WIN32) && !defined(__CYGWIN__)
	DWORD err = GetLastError();

	_dosmaperr(err);

	/*
	* Modern NT-based Windows versions return ERROR_SHARING_VIOLATION if
	* another process has the file open without FILE_SHARE_DELETE.
	* ERROR_LOCK_VIOLATION has also been seen with some anti-virus
	* software. This used to check for just ERROR_ACCESS_DENIED, so
	* presumably you can get that too with some OS versions. We don't
	* expect real permission errors where we currently use rename().
	*/
	if (err != ERROR_ACCESS_DENIED &&
	err != ERROR_SHARING_VIOLATION &&
	err != ERROR_LOCK_VIOLATION)
	return -1;
	#else
	if (errno != EACCES)
	return -1;
	#endif

	if (++loops > 100) /* time out after 10 sec */
	return -1;
	pg_usleep(100000); /* us */
	}
	return 0;
	}

	/*
	* Check if _pglstat64()'s reason for failure was STATUS_DELETE_PENDING.
	* This doesn't apply to Cygwin, which has its own lstat() that would report
	* the case as EACCES.
	*/
	static bool
	lstat_error_was_status_delete_pending(void)
	{
	if (errno != ENOENT)
	return false;
	#if defined(WIN32) && !defined(__CYGWIN__)
	if (pg_RtlGetLastNtStatus() == STATUS_DELETE_PENDING)
	return true;
	#endif
	return false;
	}

	/*
	* pgunlink
	*/
	int
	pgunlink(const char *path)
	{
	bool is_lnk;
	int loops = 0;
	struct stat st;

	/*
	* This function might be called for a regular file or for a junction
	* point (which we use to emulate symlinks). The latter must be unlinked
	* with rmdir() on Windows. Before we worry about any of that, let's see
	* if we can unlink directly, since that's expected to be the most common
	* case.
	*/
	if (unlink(path) == 0)
	return 0;
	if (errno != EACCES)
	return -1;

	/*
	* EACCES is reported for many reasons including unlink() of a junction
	* point. Check if that's the case so we can redirect to rmdir().
	*
	* Note that by checking only once, we can't cope with a path that changes
	* from regular file to junction point underneath us while we're retrying
	* due to sharing violations, but that seems unlikely. We could perhaps
	* prevent that by holding a file handle ourselves across the lstat() and
	* the retry loop, but that seems like over-engineering for now.
	*
	* In the special case of a STATUS_DELETE_PENDING error (file already
	* unlinked, but someone still has it open), we don't want to report
	* ENOENT to the caller immediately, because rmdir(parent) would probably
	* fail. We want to wait until the file truly goes away so that simple
	* recursive directory unlink algorithms work.
	*/
	if (lstat(path, &st) < 0)
	{
	if (lstat_error_was_status_delete_pending())
	is_lnk = false;
	else
	return -1;
	}
	else
	is_lnk = S_ISLNK(st.st_mode);

	/*
	* We need to loop because even though PostgreSQL uses flags that allow
	* unlink while the file is open, other applications might have the file
	* open without those flags. However, we won't wait indefinitely for
	* someone else to close the file, as the caller might be holding locks
	* and blocking other backends.
	*/
	while ((is_lnk ? rmdir(path) : unlink(path)) < 0)
	{
	if (errno != EACCES)
	return -1;
	if (++loops > 100) /* time out after 10 sec */
	return -1;
	pg_usleep(100000); /* us */
	}
	return 0;
	}

	/* We undefined these above; now redefine for possible use below */
	#define rename(from, to) pgrename(from, to)
	#define unlink(path) pgunlink(path)
	#endif /* defined(WIN32) \|\| defined(__CYGWIN__) */


	#if defined(WIN32) && !defined(__CYGWIN__) /* Cygwin has its own symlinks */

	/*
	* pgsymlink support:
	*
	* This struct is a replacement for REPARSE_DATA_BUFFER which is defined in VC6 winnt.h
	* but omitted in later SDK functions.
	* We only need the SymbolicLinkReparseBuffer part of the original struct's union.
	*/
	typedef struct
	{
	DWORD ReparseTag;
	WORD ReparseDataLength;
	WORD Reserved;
	/* SymbolicLinkReparseBuffer */
	WORD SubstituteNameOffset;
	WORD SubstituteNameLength;
	WORD PrintNameOffset;
	WORD PrintNameLength;
	WCHAR PathBuffer[FLEXIBLE_ARRAY_MEMBER];
	} REPARSE_JUNCTION_DATA_BUFFER;

	#define REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE \
	FIELD_OFFSET(REPARSE_JUNCTION_DATA_BUFFER, SubstituteNameOffset)


	/*
	* pgsymlink - uses Win32 junction points
	*
	* For reference: http://www.codeproject.com/KB/winsdk/junctionpoints.aspx
	*/
	int
	pgsymlink(const char oldpath, const char newpath)
	{
	HANDLE dirhandle;
	DWORD len;
	char buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
	char nativeTarget[MAX_PATH];
	char *p = nativeTarget;
	REPARSE_JUNCTION_DATA_BUFFER reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER ) buffer;

	CreateDirectory(newpath, 0);
	dirhandle = CreateFile(newpath, GENERIC_READ \| GENERIC_WRITE,
	0, 0, OPEN_EXISTING,
	FILE_FLAG_OPEN_REPARSE_POINT \| FILE_FLAG_BACKUP_SEMANTICS, 0);

	if (dirhandle == INVALID_HANDLE_VALUE)
	{
	_dosmaperr(GetLastError());
	return -1;
	}

	/* make sure we have an unparsed native win32 path */
	if (memcmp("\\??\\", oldpath, 4) != 0)
	snprintf(nativeTarget, sizeof(nativeTarget), "\\??\\%s", oldpath);
	else
	strlcpy(nativeTarget, oldpath, sizeof(nativeTarget));

	while ((p = strchr(p, '/')) != NULL)
	*p++ = '\\';

	len = strlen(nativeTarget) * sizeof(WCHAR);
	reparseBuf->ReparseTag = IO_REPARSE_TAG_MOUNT_POINT;
	reparseBuf->ReparseDataLength = len + 12;
	reparseBuf->Reserved = 0;
	reparseBuf->SubstituteNameOffset = 0;
	reparseBuf->SubstituteNameLength = len;
	reparseBuf->PrintNameOffset = len + sizeof(WCHAR);
	reparseBuf->PrintNameLength = 0;
	MultiByteToWideChar(CP_ACP, 0, nativeTarget, -1,
	reparseBuf->PathBuffer, MAX_PATH);

	/*
	* FSCTL_SET_REPARSE_POINT is coded differently depending on SDK version;
	* we use our own definition
	*/
	if (!DeviceIoControl(dirhandle,
	CTL_CODE(FILE_DEVICE_FILE_SYSTEM, 41, METHOD_BUFFERED, FILE_ANY_ACCESS),
	reparseBuf,
	reparseBuf->ReparseDataLength + REPARSE_JUNCTION_DATA_BUFFER_HEADER_SIZE,
	0, 0, &len, 0))
	{
	LPSTR msg;
	int save_errno;

	_dosmaperr(GetLastError());
	save_errno = errno;

	FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER \|
	FORMAT_MESSAGE_IGNORE_INSERTS \|
	FORMAT_MESSAGE_FROM_SYSTEM,
	NULL, GetLastError(),
	MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
	(LPSTR) &msg, 0, NULL);
	#ifndef FRONTEND
	ereport(ERROR,
	(errcode_for_file_access(),
	errmsg("could not set junction for \"%s\": %s",
	nativeTarget, msg)));
	#else
	fprintf(stderr, _("could not set junction for \"%s\": %s\n"),
	nativeTarget, msg);
	#endif
	LocalFree(msg);

	CloseHandle(dirhandle);
	RemoveDirectory(newpath);

	errno = save_errno;

	return -1;
	}

	CloseHandle(dirhandle);

	return 0;
	}

	/*
	* pgreadlink - uses Win32 junction points
	*/
	int
	pgreadlink(const char path, char buf, size_t size)
	{
	DWORD attr;
	HANDLE h;
	char buffer[MAX_PATH * sizeof(WCHAR) + offsetof(REPARSE_JUNCTION_DATA_BUFFER, PathBuffer)];
	REPARSE_JUNCTION_DATA_BUFFER reparseBuf = (REPARSE_JUNCTION_DATA_BUFFER ) buffer;
	DWORD len;
	int r;

	attr = GetFileAttributes(path);
	if (attr == INVALID_FILE_ATTRIBUTES)
	{
	_dosmaperr(GetLastError());
	return -1;
	}
	if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == 0)
	{
	errno = EINVAL;
	return -1;
	}

	h = CreateFile(path,
	GENERIC_READ,
	FILE_SHARE_READ \| FILE_SHARE_WRITE,
	NULL,
	OPEN_EXISTING,
	FILE_FLAG_OPEN_REPARSE_POINT \| FILE_FLAG_BACKUP_SEMANTICS,
	0);
	if (h == INVALID_HANDLE_VALUE)
	{
	_dosmaperr(GetLastError());
	return -1;
	}

	if (!DeviceIoControl(h,
	FSCTL_GET_REPARSE_POINT,
	NULL,
	0,
	(LPVOID) reparseBuf,
	sizeof(buffer),
	&len,
	NULL))
	{
	LPSTR msg;

	errno = 0;
	FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER \|
	FORMAT_MESSAGE_IGNORE_INSERTS \|
	FORMAT_MESSAGE_FROM_SYSTEM,
	NULL, GetLastError(),
	MAKELANGID(LANG_ENGLISH, SUBLANG_DEFAULT),
	(LPSTR) &msg, 0, NULL);
	#ifndef FRONTEND
	ereport(ERROR,
	(errcode_for_file_access(),
	errmsg("could not get junction for \"%s\": %s",
	path, msg)));
	#else
	fprintf(stderr, _("could not get junction for \"%s\": %s\n"),
	path, msg);
	#endif
	LocalFree(msg);
	CloseHandle(h);
	errno = EINVAL;
	return -1;
	}
	CloseHandle(h);

	/* Got it, let's get some results from this */
	if (reparseBuf->ReparseTag != IO_REPARSE_TAG_MOUNT_POINT)
	{
	errno = EINVAL;
	return -1;
	}

	r = WideCharToMultiByte(CP_ACP, 0,
	reparseBuf->PathBuffer, -1,
	buf,
	size,
	NULL, NULL);

	if (r <= 0)
	{
	errno = EINVAL;
	return -1;
	}

	/* r includes the null terminator */
	r -= 1;

	/*
	* If the path starts with "\??\" followed by a "drive absolute" path
	* (known to Windows APIs as RtlPathTypeDriveAbsolute), then strip that
	* prefix. This undoes some of the transformation performed by
	* pgsymlink(), to get back to a format that users are used to seeing. We
	* don't know how to transform other path types that might be encountered
	* outside PGDATA, so we just return them directly.
	*/
	if (r >= 7 &&
	buf[0] == '\\' &&
	buf[1] == '?' &&
	buf[2] == '?' &&
	buf[3] == '\\' &&
	isalpha(buf[4]) &&
	buf[5] == ':' &&
	buf[6] == '\\')
	{
	memmove(buf, buf + 4, strlen(buf + 4) + 1);
	r -= 4;
	}
	return r;
	}

	#endif /* defined(WIN32) && !defined(__CYGWIN__) */