Replace pgwin32_is_junction() with lstat().

Now that lstat() reports junction points with S_IFLNK/S_ISLINK(), and
unlink() can unlink them, there is no need for conditional code for
Windows in a few places.  That was expressed by testing for WIN32 or
S_ISLNK, which we can now constant-fold.

The coding around pgwin32_is_junction() was a bit suspect anyway, as we
never checked for errors, and we also know that errors can be spuriously
reported because of transient sharing violations on this OS.  The
lstat()-based code has handling for that.

This also reverts 4fc6b6ee on master only.  That was done because
lstat() didn't previously work for symlinks (junction points), but now
it does.

Tested-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/CA%2BhUKGLfOOeyZpm5ByVcAt7x5Pn-%3DxGRNCvgiUPVVzjFLtnY0w%40mail.gmail.com
(cherry picked from commit 5fc88c5d53)

Author: Thomas Munro <tmunro@postgresql.org>
Author: Alexandra Wang <alexandra.wang.oss@gmail.com>

src/backend/commands/tablespace.c

@@ -787,8 +787,7 @@ destroy_tablespace_directories(Oid tablespaceoid, bool redo)
 	/*
 	 * Try to remove the symlink.  We must however deal with the possibility
 	 * that it's a directory instead of a symlink --- this could happen during
-	 * WAL replay (see TablespaceCreateDbspace), and it is also the case on
+	 * WAL replay (see TablespaceCreateDbspace).
-	 * Windows where junction points lstat() as directories.
 	 *
 	 * Note: in the redo case, we'll return true if this final step fails;
 	 * there's no point in retrying it.  Also, ENOENT should provoke no more
@@ -818,7 +817,6 @@ remove_symlink:
 							linkloc)));
 		}
 	}
-#ifdef S_ISLNK
 	else if (S_ISLNK(st.st_mode))
 	{
 		if (unlink(linkloc) < 0)
@@ -831,7 +829,6 @@ remove_symlink:
 							linkloc)));
 		}
 	}
-#endif
 	else
 	{
 		/* Refuse to remove anything that's not a directory or symlink */
@@ -909,7 +906,6 @@ remove_tablespace_symlink(const char *linkloc)
 					 errmsg("could not remove directory \"%s\": %m",
 							linkloc)));
 	}
-#ifdef S_ISLNK
 	else if (S_ISLNK(st.st_mode))
 	{
 		if (unlink(linkloc) < 0 && errno != ENOENT)
@@ -918,7 +914,6 @@ remove_tablespace_symlink(const char *linkloc)
 					 errmsg("could not remove symbolic link \"%s\": %m",
 							linkloc)));
 	}
-#endif
 	else
 	{
 		/* Refuse to remove anything that's not a directory or symlink */

src/backend/replication/basebackup.c

@@ -1415,13 +1415,7 @@ sendDir(const char *path, int basepathlen, bool sizeonly, List *tablespaces,
 		}
 
 		/* Allow symbolic links in pg_tblspc only */
-		if (strcmp(path, "./pg_tblspc") == 0 &&
+		if (strcmp(path, "./pg_tblspc") == 0 && S_ISLNK(statbuf.st_mode))
-#ifndef WIN32
-			S_ISLNK(statbuf.st_mode)
-#else
-			pgwin32_is_junction(pathbuf)
-#endif
-			)
 		{
 #if defined(HAVE_READLINK) || defined(WIN32)
 			char		linkpath[MAXPGPATH];
@@ -1884,11 +1878,7 @@ _tarWriteDir(const char *pathbuf, int basepathlen, struct stat *statbuf,
 			 bool sizeonly)
 {
 	/* If symlink, write it as a directory anyway */
-#ifndef WIN32
 	if (S_ISLNK(statbuf->st_mode))
-#else
-	if (pgwin32_is_junction(pathbuf))
-#endif
 		statbuf->st_mode = S_IFDIR | pg_dir_create_mode;
 
 	return _tarWriteHeader(pathbuf + basepathlen + 1, NULL, statbuf, sizeonly);

src/backend/storage/file/fd.c

@@ -3351,7 +3351,6 @@ SyncDataDirectory(void)
 	 */
 	xlog_is_symlink = false;
 
-#ifndef WIN32
 	{
 		struct stat st;
 
@@ -3363,10 +3362,6 @@ SyncDataDirectory(void)
 		else if (S_ISLNK(st.st_mode))
 			xlog_is_symlink = true;
 	}
-#else
-	if (pgwin32_is_junction("pg_wal"))
-		xlog_is_symlink = true;
-#endif
 
 #ifdef HAVE_SYNCFS
 	if (recovery_init_sync_method == RECOVERY_INIT_SYNC_METHOD_SYNCFS)

src/backend/utils/adt/misc.c

@@ -310,9 +310,7 @@ pg_tablespace_location(PG_FUNCTION_ARGS)
 	char		sourcepath[MAXPGPATH];
 	char		targetpath[MAXPGPATH];
 	int			rllen;
-#ifndef WIN32
 	struct stat st;
-#endif
 
 	/*
 	 * It's useful to apply this function to pg_class.reltablespace, wherein
@@ -343,10 +341,6 @@ pg_tablespace_location(PG_FUNCTION_ARGS)
 	 * created with allow_in_place_tablespaces enabled.  If a directory is
 	 * found, a relative path to the data directory is returned.
 	 */
-#ifdef WIN32
-	if (!pgwin32_is_junction(sourcepath))
-		PG_RETURN_TEXT_P(cstring_to_text(sourcepath));
-#else
 	if (lstat(sourcepath, &st) < 0)
 	{
 		ereport(ERROR,
@@ -357,7 +351,6 @@ pg_tablespace_location(PG_FUNCTION_ARGS)
 
 	if (!S_ISLNK(st.st_mode))
 		PG_RETURN_TEXT_P(cstring_to_text(sourcepath));
-#endif
 
 	/*
 	 * In presence of a link or a junction point, return the path pointing to.

src/bin/pg_checksums/pg_checksums.c

@@ -391,11 +391,7 @@ scan_directory(const char *basedir, const char *subdir, bool sizeonly)
 			if (!sizeonly)
 				scan_file(fn, segmentno);
 		}
-#ifndef WIN32
 		else if (S_ISDIR(st.st_mode) || S_ISLNK(st.st_mode))
-#else
-		else if (S_ISDIR(st.st_mode) || pgwin32_is_junction(fn))
-#endif
 		{
 			/*
 			 * If going through the entries of pg_tblspc, we assume to operate

src/bin/pg_rewind/file_ops.c

@@ -431,11 +431,7 @@ recurse_dir(const char *datadir, const char *parentpath,
 			/* recurse to handle subdirectories */
 			recurse_dir(datadir, path, callback);
 		}
-#ifndef WIN32
 		else if (S_ISLNK(fst.st_mode))
-#else
-		else if (pgwin32_is_junction(fullpath))
-#endif
 		{
 #if defined(HAVE_READLINK) || defined(WIN32)
 			char		link_target[MAXPGPATH];

src/common/file_utils.c

@@ -79,7 +79,6 @@ fsync_pgdata(const char *pg_data,
 	 */
 	xlog_is_symlink = false;
 
-#ifndef WIN32
 	{
 		struct stat st;
 
@@ -88,10 +87,6 @@ fsync_pgdata(const char *pg_data,
 		else if (S_ISLNK(st.st_mode))
 			xlog_is_symlink = true;
 	}
-#else
-	if (pgwin32_is_junction(pg_wal))
-		xlog_is_symlink = true;
-#endif
 
 	/*
 	 * If possible, hint to the kernel that we're soon going to fsync the data
@@ -459,27 +454,9 @@ get_dirent_type(const char *path,
 			result = PGFILETYPE_REG;
 		else if (S_ISDIR(fst.st_mode))
 			result = PGFILETYPE_DIR;
-#ifdef S_ISLNK
 		else if (S_ISLNK(fst.st_mode))
 			result = PGFILETYPE_LNK;
-#endif
 	}
 
-#if defined(WIN32) && !defined(_MSC_VER)
-
-	/*
-	 * If we're on native Windows (not Cygwin, which has its own POSIX
-	 * symlinks), but not using the MSVC compiler, then we're using a
-	 * readdir() emulation provided by the MinGW runtime that has no d_type.
-	 * Since the lstat() fallback code reports junction points as directories,
-	 * we need an extra system call to check if we should report them as
-	 * symlinks instead, following our convention.
-	 */
-	if (result == PGFILETYPE_DIR &&
-		!look_through_symlinks &&
-		pgwin32_is_junction(path))
-		result = PGFILETYPE_LNK;
-#endif
-
 	return result;
 }

src/include/port.h

@@ -284,7 +284,6 @@ extern int	pgunlink(const char *path);
 #if defined(WIN32) && !defined(__CYGWIN__)
 extern int	pgsymlink(const char *oldpath, const char *newpath);
 extern int	pgreadlink(const char *path, char *buf, size_t size);
-extern bool pgwin32_is_junction(const char *path);
 
 #define symlink(oldpath, newpath)	pgsymlink(oldpath, newpath)
 #define readlink(path, buf, size)	pgreadlink(path, buf, size)

src/include/port/win32_port.h

@@ -228,7 +228,6 @@ extern pgoff_t _pgftello64(FILE *stream);
  */
 extern int	pgsymlink(const char *oldpath, const char *newpath);
 extern int	pgreadlink(const char *path, char *buf, size_t size);
-extern bool pgwin32_is_junction(const char *path);
 
 #define symlink(oldpath, newpath)	pgsymlink(oldpath, newpath)
 #define readlink(path, buf, size)	pgreadlink(path, buf, size)

src/port/dirmod.c

@@ -362,20 +362,4 @@ pgreadlink(const char *path, char *buf, size_t size)
 	return r;
 }
 
-/*
- * Assumes the file exists, so will return false if it doesn't
- * (since a nonexistent file is not a junction)
- */
-bool
-pgwin32_is_junction(const char *path)
-{
-	DWORD		attr = GetFileAttributes(path);
-
-	if (attr == INVALID_FILE_ATTRIBUTES)
-	{
-		_dosmaperr(GetLastError());
-		return false;
-	}
-	return ((attr & FILE_ATTRIBUTE_REPARSE_POINT) == FILE_ATTRIBUTE_REPARSE_POINT);
-}
 #endif							/* defined(WIN32) && !defined(__CYGWIN__) */