Re: [patch 2.6.22-git] dev_vdbg(), available with -DVERBOSE_DEBUG

[David Brownell]

On Thursday 12 July 2007, Andrew Morton wrote:
> On Thu, 12 Jul 2007 20:30:49 -0700 David Brownell <david-b@xxxxxxxxxxx> wrote:
> 
> > This defines a dev_vdbg() call, which is enabled with -DVERBOSE_DEBUG.
> > When enabled, dev_vdbg() acts just like dev_dbg().  When disabled, it
> > is a NOP ... just like dev_dbg() without -DDEBUG.  The specific code
> > was moved out of a USB patch, but lots of drivers have similar support.
> 
> I suppose we should find some way of telling people about this.  Maybe
> in the `make help' output?

Whereever people learn about "-DDEBUG", they should probably
be able to learn about "-DVERBOSE_DEBUG".  Which is likely
from existing kernel code (although most C coders will expect
that "-DDEBUG" does *something* interesting).

I suspect maybe Documentation/CodingStyle would be better..

- Dave

====	CUT HERE
Update CodingStyle to talk about "-DDEBUG" message conventions and the
new "-DVERBOSE_DEBUG" convention.

Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
---
 Documentation/CodingStyle |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

--- g26.orig/Documentation/CodingStyle	2007-07-12 23:03:25.000000000 -0700
+++ g26/Documentation/CodingStyle	2007-07-12 23:53:52.000000000 -0700
@@ -621,12 +621,27 @@ covers RTL which is used frequently with
 
 Kernel developers like to be seen as literate. Do mind the spelling
 of kernel messages to make a good impression. Do not use crippled
-words like "dont" and use "do not" or "don't" instead.
+words like "dont"; use "do not" or "don't" instead.  Make the messages
+concise, clear, and unambiguous.
 
 Kernel messages do not have to be terminated with a period.
 
 Printing numbers in parentheses (%d) adds no value and should be avoided.
 
+There are a number of driver model diagnostic macros in <linux/device.h>
+which you should use to make sure messages are matched to the right device
+and driver, and are tagged with the right level:  dev_err(), dev_warn(),
+dev_info(), and so forth.  For messages that aren't associated with a
+particular device, <linux/kernel.h> defines pr_debug() and pr_info().
+
+Coming up with good debugging messages can be quite a challenge; and once
+you have them, they can be a huge help for remote troubleshooting.  Such
+messages should be compiled out when the DEBUG symbol is not defined (that
+is, by default they are not included).  When you use dev_dbg() or pr_debug(),
+that's automatic.  Many subsystems have Kconfig options to turn on -DDEBUG.
+A related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to the
+ones already enabled by DEBUG.
+
 
 		Chapter 14: Allocating memory
 
@@ -751,4 +766,5 @@ Kernel CodingStyle, by greg@xxxxxxxxx at
 http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/
 
 --
-Last updated on 2006-December-06.
+Last updated on 2007-July-13.
+

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