linux-kernel - Re: [PATCH 1/1] Add documentation for proper usage and order of preference of calls to print diagnostic messages.

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Date:	Tue, 04 Mar 2014 08:27:59 -0800
From:	Randy Dunlap <rdunlap@...radead.org>
To:	yogesh <mr.yogesh@...il.com>, Levente Kurusa <levex@...ux.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH 1/1] Add documentation for proper usage and order of preference
 of calls to print diagnostic messages.

On 03/04/2014 06:31 AM, yogesh wrote:
> This patch adds documentation that clarifies the use of various
> diagnostic printing messages. It shows the preference of subsystem_dbg
> calls to dev_dbg (whenever possible), as they first preferred format of
> logging debug messages.
> Signed-off-by: Yogesh Chaudhari <mr.yogesh@...il.com>
> ---
>  Documentation/CodingStyle | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
> index 7fe0546..083f738 100644
> --- a/Documentation/CodingStyle
> +++ b/Documentation/CodingStyle
> @@ -662,6 +662,23 @@ 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/printk.h> defines pr_debug() and pr_info().
>  
> +If the subsystem has its own diagnostic macros then they should be used
> +instead of dev_dbg calls.
> +e.g. If you are using network subsystem, use netdev_dbg;

   E.g., if you are

> +if you are using V4L, use v4l_dbg etc.
> +This standardises the output format in every subsystem.
> +
> +Depending on your changes, the following order of precedence
> +applies to printing messages:
> +1. [subsystem]_dbg() is preferred when the subsystem has its own
> +diagnostic macros.
> +2. dev_dbg() is preferred when you have a generic struct device object.
> +3. pr_debug() should be used when 1 and 2 above are not applicable.
> +4. printk() should be avoided.
> +
> +Note: The above order applies to diagnostic calls of all log levels viz:
> +*_emerg, *_alert, *_crit, *_err, *_warn, *_notice, *_info and *_dbg.
> +
>  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
> --


-- 
~Randy
--
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