2 files changed, 20 insertions, 8 deletions

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 61a2109bc04..12eabe46e5a 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,5 +1,11 @@
 2007-09-30  David Kastrup  <dak@gnu.org>
 
+        * autorevert.el (auto-revert-handler): In `auto-revert-tail-mode',
+        check only for changed size.
+        (auto-revert-tail-handler): Get size from caller.  If the file has
+        shrunk, tail the whole file again (the file presumably has been
+        rewritten).
+
         * woman.el (woman-topic-all-completions, woman-mini-help): Fix
         fallout from 2007-09-07 introduction of `dolist' when the list
         actually was being manipulated in the loop.
diff --git a/lisp/autorevert.el b/lisp/autorevert.el
index f1e5b146058..49e83c514a9 100644
--- a/lisp/autorevert.el
+++ b/lisp/autorevert.el
@@ -416,12 +416,16 @@ will use an up-to-date value of `auto-revert-interval'"
   "Revert current buffer, if appropriate.
 This is an internal function used by Auto-Revert Mode."
   (when (or auto-revert-tail-mode (not (buffer-modified-p)))
-    (let* ((buffer (current-buffer))
+    (let* ((buffer (current-buffer)) size
            (revert
             (or (and buffer-file-name
                      (not (file-remote-p buffer-file-name))
                      (file-readable-p buffer-file-name)
-                     (not (verify-visited-file-modtime buffer)))
+                     (if auto-revert-tail-mode
+                         (/= auto-revert-tail-pos
+                            (setq size
+                                  (nth 7 (file-attributes buffer-file-name))))
+                       (not (verify-visited-file-modtime buffer))))
                 (and (or auto-revert-mode
                          global-auto-revert-non-file-buffers)
                      revert-buffer-function
@@ -445,7 +449,7 @@ This is an internal function used by Auto-Revert Mode."
                     (push window eoblist)))
            'no-mini t))
         (if auto-revert-tail-mode
-            (auto-revert-tail-handler)
+            (auto-revert-tail-handler size)
           ;; Bind buffer-read-only in case user has done C-x C-q,
           ;; so as not to forget that.  This gives undesirable results
           ;; when the file's mode changes, but that is less common.
@@ -460,20 +464,22 @@ This is an internal function used by Auto-Revert Mode."
       (when (or revert auto-revert-check-vc-info)
         (vc-find-file-hook)))))
 
-(defun auto-revert-tail-handler ()
-  (let ((size (nth 7 (file-attributes buffer-file-name)))
-        (modified (buffer-modified-p))
+(defun auto-revert-tail-handler (size)  
+  (let ((modified (buffer-modified-p))
         (inhibit-read-only t)           ; Ignore.
         (file buffer-file-name)
         (buffer-file-name nil))         ; Ignore that file has changed.
-    (when (> size auto-revert-tail-pos)
+    (when (/= auto-revert-tail-pos size)
       (run-hooks 'before-revert-hook)
       (undo-boundary)
       (save-restriction
         (widen)
         (save-excursion
           (goto-char (point-max))
-          (insert-file-contents file nil auto-revert-tail-pos size)))
+          (insert-file-contents file nil
+                                (and (< auto-revert-tail-pos size)
+                                     auto-revert-tail-pos)
+                                size)))
       (run-hooks 'after-revert-hook)
       (undo-boundary)
       (setq auto-revert-tail-pos size)