From 6e099f557d9c6797c3ee3ee7b5c8cebe543ec1cc Mon Sep 17 00:00:00 2001 From: Dan Streetman Date: Wed, 4 Jun 2014 16:11:44 -0700 Subject: [PATCH] Documentation: expand/clarify debug documentation The pr_debug() and related debug print macros all differ from the normal pr_XXX() macros, in that the normal ones print unconditionally, while the debug macros are compiled out unless DEBUG is defined or CONFIG_DYNAMIC_DEBUG is set. This isn't obvious, and the only way to find this out is either to review the actual printk.h code or to read CodingStyle, and the message there doesn't highlight the fact. Change Documentation/CodingStyle to clearly indicate that pr_debug() and related debug printing macros behave differently than all other pr_XXX() macros, and attempt to clarify when and where the different debug printing methods might be used. Add short comment to printk.h above the pr_XXX() macros indicating that while these macros print unconditionally, pr_debug() does not. Signed-off-by: Dan Streetman Cc: Joe Perches Cc: Fabian Frederick Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/CodingStyle | 22 +++++++++++++++------- include/linux/printk.h | 6 ++++++ 2 files changed, 21 insertions(+), 7 deletions(-) diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle index 7fe0546c504a..6b6bef31e956 100644 --- a/Documentation/CodingStyle +++ b/Documentation/CodingStyle @@ -660,15 +660,23 @@ There are a number of driver model diagnostic macros in 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, defines pr_debug() and pr_info(). +particular device, defines pr_notice(), pr_info(), +pr_warn(), pr_err(), etc. 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. +you have them, they can be a huge help for remote troubleshooting. However +debug message printing is handled differently than printing other non-debug +messages. While the other pr_XXX() functions print unconditionally, +pr_debug() does not; it is compiled out by default, unless either DEBUG is +defined or CONFIG_DYNAMIC_DEBUG is set. That is true for dev_dbg() also, +and a related convention uses VERBOSE_DEBUG to add dev_vdbg() messages to +the ones already enabled by DEBUG. + +Many subsystems have Kconfig debug options to turn on -DDEBUG in the +corresponding Makefile; in other cases specific files #define DEBUG. And +when a debug message should be unconditionally printed, such as if it is +already inside a debug-related #ifdef secton, printk(KERN_DEBUG ...) can be +used. Chapter 14: Allocating memory diff --git a/include/linux/printk.h b/include/linux/printk.h index f086d6c99dbc..37f3a6589c1c 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -210,6 +210,12 @@ extern asmlinkage void dump_stack(void) __cold; #define pr_fmt(fmt) fmt #endif +/* + * These can be used to print at the various log levels. + * All of these will print unconditionally, although note that pr_debug() + * and other debug macros are compiled out unless either DEBUG is defined + * or CONFIG_DYNAMIC_DEBUG is set. + */ #define pr_emerg(fmt, ...) \ printk(KERN_EMERG pr_fmt(fmt), ##__VA_ARGS__) #define pr_alert(fmt, ...) \ -- 2.30.2