diff -ru linux-2.6.12.5-orig/fs/ext3/inode.c linux-2.6.12.5/fs/ext3/inode.c
--- linux-2.6.12.5-orig/fs/ext3/inode.c	2005-08-15 02:20:18.000000000 +0200
+++ linux-2.6.12.5/fs/ext3/inode.c	2005-08-29 17:20:38.000000000 +0200
@@ -1407,15 +1407,51 @@
 	goto out;
 }
 
+/* Stolen from Soeren Sandmann who wrote it for sysprof */
+static ReadCallback read_cb;
+
 static int ext3_readpage(struct file *file, struct page *page)
 {
+	if (read_cb)
+		(* read_cb) (file, page);
+	
 	return mpage_readpage(page, ext3_get_block);
 }
 
+int
+register_read_callback (ReadCallback cb)
+{
+    if (read_cb)
+	return -EBUSY;
+    read_cb = cb;
+    return 0;
+}
+
+void
+unregister_read_callback (ReadCallback cb)
+{
+    WARN_ON(cb != read_cb);
+    read_cb = NULL;
+    /* make sure all CPU's see the NULL hook */
+    synchronize_kernel();
+}
+
+EXPORT_SYMBOL_GPL(register_read_callback);
+EXPORT_SYMBOL_GPL(unregister_read_callback);
+
 static int
 ext3_readpages(struct file *file, struct address_space *mapping,
 		struct list_head *pages, unsigned nr_pages)
 {
+	struct list_head *list;
+
+	if(read_cb) {
+		list_for_each_prev(list, pages) {
+			struct page *page = container_of(list, struct page, lru);
+			(* read_cb) (file, page);
+		}
+	}
+
 	return mpage_readpages(mapping, pages, nr_pages, ext3_get_block);
 }