--- README.txt	2009-09-05 16:24:50.000000000 +0300
+++ README.txt.new	2010-11-23 11:02:10.000000000 +0200
@@ -41,6 +41,7 @@
     'path' => 'sites/default/files/filecache',
     'static' => FALSE,
     'fast_cache' => TRUE,
+    'lock_dir' => '/absolute/path/to/your/sites/default/files/filecache',
   ),
 );
 
@@ -75,6 +76,21 @@
 localization) that do their own static storage. Advanced feature, use at own 
 discretion.
 
+lock_dir is only needed if you run PHP in safe mode, and neither system's /tmp
+nor PHP's configured 'upload_tmp_dir' paths are writable by your webserver.
+You should configure lock_dir if you get these errors in admin/dblog:
+fopen() [<a href='function.fopen'>function.fopen</a>]: SAFE MODE Restriction in effect. The script whose uid is X is not allowed to access /tmp owned by uid 0 in file [snip]/sites/all/modules/cacherouter/Cache.php on line 110
+fopen(/tmp/prefix-cache_menu_lock) [<a href='function.fopen'>function.fopen</a>]: failed to open stream: Success in file [snip]/sites/all/modules/cacherouter/Cache.php on line 110.
+flock() expects parameter 1 to be resource, boolean given in file [snip]/sites/all/modules/cacherouter/Cache.php on line 111.
+unlink() [<a href='function.unlink'>function.unlink</a>]: SAFE MODE Restriction in effect. The script whose uid is X is not allowed to access /tmp owned by uid 0 in file [snip]/sites/all/modules/cacherouter/Cache.php on line 124.
+
+You must use an absolute path if specifying a relative lock_dir still produces
+these (very similar, but now caused by open_basedir restriction) errors:
+fopen() [<a href='function.fopen'>function.fopen</a>]: open_basedir restriction in effect. File(sites/default/files/filecache/prefix-cache_page_lock) is not within the allowed path(s): (/usr/lib/php:/tmp:/usr/share/pear:/usr/share/php:/usr/local/lib/php/phplib:) in file [snip]/sites/all/modules/cacherouter/Cache.php on line 110.
+fopen(sites/default/files/filecache/prefix-cache_page_lock) [<a href='function.fopen'>function.fopen</a>]: failed to open stream: Operation not permitted in file [snip]/sites/all/modules/cacherouter/Cache.php on line 110.
+flock() expects parameter 1 to be resource, boolean given in file [snip]/sites/all/modules/cacherouter/Cache.php on line 111.
+unlink() [<a href='function.unlink'>function.unlink</a>]: Unable to access sites/default/files/filecache/prefix-cache_page_lock in file [snip]/sites/all/modules/cacherouter/Cache.php on line 124.
+
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 - TODO -
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