Commit 6b09448a authored by David Brownell's avatar David Brownell Committed by Greg Kroah-Hartman

dev_vdbg() documentation

Update CodingStyle to talk about "-DDEBUG" message conventions and the
new "-DVERBOSE_DEBUG" convention.
Signed-off-by: default avatarDavid Brownell <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent aebdc3b4
......@@ -633,12 +633,27 @@ covers RTL which is used frequently with assembly language in the kernel.
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
......@@ -790,4 +805,5 @@ Kernel CodingStyle, by at OLS 2002:
Last updated on 2006-December-06.
Last updated on 2007-July-13.
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