[PATCH -mm] documentation: update CodingStyle tips for Emacs users v2

[Johannes Weiner <hannes@saeurebad.de>]

Hi,

Jonathan Corbet <corbet@lwn.net> writes:

> On Sat, 05 Jul 2008 11:36:44 +0000
> Johannes Weiner <hannes@saeurebad.de> wrote:
>
>> A heuristics seems overkill as this snippet is not distributed code
>> that needs to be portable but it is just a tip for ones .emacs. 
>
> You're right, it's fine the way it is.

Okay, I fixed the file->filename mistake.  How about the following?

	Hannes

---
From: Johannes Weiner <hannes@saeurebad.de>
Subject: documentation: update CodingStyle tips for Emacs users

Describe a setup that integrates better with Emacs' cc-mode and also
fixes up the alignment of continuation lines to really only use tabs.

Signed-off-by: Johannes Weiner <hannes@saeurebad.de>
CC: Jonathan Corbet <corbet@lwn.net>
---

diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index 6caa146..1875e50 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -474,25 +474,29 @@ make a good program).
 So, you can either get rid of GNU emacs, or change it to use saner
 values.  To do the latter, you can stick the following in your .emacs file:
 
-(defun linux-c-mode ()
-  "C mode with adjusted defaults for use with the Linux kernel."
-  (interactive)
-  (c-mode)
-  (c-set-style "K&R")
-  (setq tab-width 8)
-  (setq indent-tabs-mode t)
-  (setq c-basic-offset 8))
-
-This will define the M-x linux-c-mode command.  When hacking on a
-module, if you put the string -*- linux-c -*- somewhere on the first
-two lines, this mode will be automatically invoked. Also, you may want
-to add
-
-(setq auto-mode-alist (cons '("/usr/src/linux.*/.*\\.[ch]$" . linux-c-mode)
-			auto-mode-alist))
-
-to your .emacs file if you want to have linux-c-mode switched on
-automagically when you edit source files under /usr/src/linux.
+(defun c-lineup-arglist-tabs-only (ignored)
+  "Line up argument lists by tabs, not spaces"
+  (let* ((anchor (c-langelem-pos c-syntactic-element))
+	 (column (c-langelem-2nd-pos c-syntactic-element))
+	 (offset (- (1+ column) anchor))
+	 (steps (floor offset c-basic-offset)))
+    (* (max steps 1)
+       c-basic-offset)))
+
+(add-hook 'c-mode-hook
+          (lambda ()
+            (let ((filename (buffer-file-name)))
+              ;; Enable kernel mode for the appropriate files
+              (when (and filename
+                         (string-match "~/src/linux-trees" filename))
+                (setq indent-tabs-mode t)
+                (c-set-style "linux")
+                (c-set-offset 'arglist-cont-nonempty
+                              '(c-lineup-gcc-asm-reg
+                                c-lineup-arglist-tabs-only))))))
+
+This will make emacs go better with the kernel coding style for C
+files below ~/src/linux-trees.
 
 But even if you fail in getting emacs to do sane formatting, not
 everything is lost: use "indent".