diff --git a/src/backend/utils/adt/genfile.c b/src/backend/utils/adt/genfile.c
index 43a05659a26e9646d1f2f79a888c9e7df626300d..cbbf9ca1c37b0ffc583c3f553a596c46745baf82 100644
--- a/src/backend/utils/adt/genfile.c
+++ b/src/backend/utils/adt/genfile.c
@@ -9,7 +9,7 @@
  * Author: Andreas Pflug <pgadmin@pse-consulting.de>
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/genfile.c,v 1.5 2005/08/15 23:00:14 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/genfile.c,v 1.6 2005/08/29 19:39:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -41,7 +41,7 @@ typedef struct
  * Validate a path and convert to absolute form.
  *
  * Argument may be absolute or relative to the DataDir (but we only allow
- * absolute paths that match Log_directory).
+ * absolute paths that match DataDir or Log_directory).
  */
 static char *
 check_and_make_absolute(text *arg)
@@ -62,11 +62,12 @@ check_and_make_absolute(text *arg)
 
 	if (is_absolute_path(filename))
 	{
+		/* Allow absolute references within DataDir */
+		if (path_is_prefix_of_path(DataDir, filename))
+			return filename;
 		/* The log directory might be outside our datadir, but allow it */
-	    if (is_absolute_path(Log_directory) &&
-			strncmp(filename, Log_directory, strlen(Log_directory)) == 0 &&
-			(filename[strlen(Log_directory)] == '/' ||
-			 filename[strlen(Log_directory)] == '\0'))
+		if (is_absolute_path(Log_directory) &&
+			path_is_prefix_of_path(Log_directory, filename))
 			return filename;
 
 	    ereport(ERROR,
diff --git a/src/include/port.h b/src/include/port.h
index ce261d9f050a357f15758cd1d81a0c4d147f11b3..7172ce5fb53f88054fb7fcdd4cc4660baa76ce38 100644
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/port.h,v 1.81 2005/08/12 21:07:52 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/port.h,v 1.82 2005/08/29 19:39:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -33,6 +33,7 @@ extern void join_path_components(char *ret_path,
 extern void canonicalize_path(char *path);
 extern void make_native_path(char *path);
 extern bool path_contains_parent_reference(const char *path);
+extern bool path_is_prefix_of_path(const char *path1, const char *path2);
 extern const char *get_progname(const char *argv0);
 extern void get_share_path(const char *my_exec_path, char *ret_path);
 extern void get_etc_path(const char *my_exec_path, char *ret_path);
diff --git a/src/port/path.c b/src/port/path.c
index 7e37bede7eaaeaebed51f3ea7f666c1997d354d2..41a505759e9a56b2aaab7246a27bdbe8e2225064 100644
--- a/src/port/path.c
+++ b/src/port/path.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/port/path.c,v 1.57 2005/08/12 21:07:53 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/port/path.c,v 1.58 2005/08/29 19:39:39 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -364,6 +364,22 @@ path_contains_parent_reference(const char *path)
 	return false;
 }
 
+/*
+ * Detect whether path1 is a prefix of path2 (including equality).
+ *
+ * This is pretty trivial, but it seems better to export a function than
+ * to export IS_DIR_SEP.
+ */
+bool
+path_is_prefix_of_path(const char *path1, const char *path2)
+{
+	int path1_len = strlen(path1);
+
+	if (strncmp(path1, path2, path1_len) == 0 &&
+		(IS_DIR_SEP(path2[path1_len]) || path2[path1_len] == '\0'))
+		return true;
+	return false;
+}
 
 /*
  * Extracts the actual name of the program as called -