Fix pg_rewind's handling of top-level symlinks.

The previous coding suffered a null-pointer dereference if it found any
symlink at the top level of $PGDATA.  Fix that, and teach it to recurse
into a symlink for pg_xlog, but not anything else.

Per note from Abhijit Menon-Sen.

diff --git a/src/bin/pg_rewind/copy_fetch.c b/src/bin/pg_rewind/copy_fetch.c
index c92744ca77245924462d4b87a6357821f52d7e3d..1ca00d12adfb2f49c15f74ccfd12c6783eef2cef 100644 (file)
--- a/src/bin/pg_rewind/copy_fetch.c
+++ b/src/bin/pg_rewind/copy_fetch.c
@@ -42,6 +42,9 @@ traverse_datadir(const char *datadir, process_file_callback_t callback)
 
 /*
  * recursive part of traverse_datadir
+ *
+ * parent_path is the current subdirectory's path relative to datadir,
+ * or NULL at the top level.
  */
 static void
 recurse_dir(const char *datadir, const char *parentpath,
@@ -127,9 +130,11 @@ recurse_dir(const char *datadir, const char *parentpath,
 
            /*
             * If it's a symlink within pg_tblspc, we need to recurse into it,
-            * to process all the tablespaces.
+            * to process all the tablespaces.  We also follow a symlink if
+            * it's for pg_xlog.  Symlinks elsewhere are ignored.
             */
-           if (strcmp(parentpath, "pg_tblspc") == 0)
+           if ((parentpath && strcmp(parentpath, "pg_tblspc") == 0) ||
+               strcmp(path, "pg_xlog") == 0)
                recurse_dir(datadir, path, callback);
 #else
            pg_fatal("\"%s\" is a symbolic link, but symbolic links are not supported on this platform\n",