diff -ru librsync-0.9.7/buf.c librsync-0.9.7-update-in-place/buf.c
--- librsync-0.9.7/buf.c	2004-02-07 15:17:57.000000000 -0800
+++ librsync-0.9.7-update-in-place/buf.c	2011-02-15 17:10:07.177068380 -0800
@@ -183,7 +183,31 @@
                 
         assert(present > 0);
 
+        /* See if we can skip the write operation.
+         * This is particularly useful when the destination
+         * is an LVM/SAN snapshot, and the new-file content is already
+         * identical to the basis-file.
+         * 
+         * Define DISABLE_UPDATE_IN_PLACE somewhere
+         * to disable this patch.
+         */
+#ifndef DISABLE_UPDATE_IN_PLACE
+        long offset;
+        char *inbuf = malloc(present);
+        assert(inbuf != NULL);
+
+        offset = ftell(f);
+        result = fread(inbuf, 1, present, f);
+        if (result != present 
+          || memcmp(inbuf, fb->buf, present) != 0)
+        {
+          fseek(f, offset, SEEK_SET);
+          result = fwrite(fb->buf, 1, present, f);
+        }
+        free(inbuf);
+#else
         result = fwrite(fb->buf, 1, present, f);
+#endif
         if (present != result) {
             rs_error("error draining buf to file: %s",
                      strerror(errno));
diff -ru librsync-0.9.7/rdiff.c librsync-0.9.7-update-in-place/rdiff.c
--- librsync-0.9.7/rdiff.c	2004-09-17 14:35:50.000000000 -0700
+++ librsync-0.9.7-update-in-place/rdiff.c	2011-02-15 16:03:26.000000000 -0800
@@ -327,7 +327,7 @@
 
     basis_file = rs_file_open(basis_name, "rb");
     delta_file = rs_file_open(poptGetArg(opcon), "rb");
-    new_file =   rs_file_open(poptGetArg(opcon), "wb");
+    new_file =   rs_file_open(poptGetArg(opcon), "wb+");
 
     rdiff_no_more_args(opcon);