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Subject[PATCH 2/2] [condingstyle] Add chapter on tests
Several standards have been established on how to format tests and use
NULL/false/true tests.

Signed-off-by: Auke Kok <>

Documentation/CodingStyle | 51 +++++++++++++++++++++++++++++++++++----------
1 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/Documentation/CodingStyle b/Documentation/CodingStyle
index f518395..3635b38 100644
--- a/Documentation/CodingStyle
+++ b/Documentation/CodingStyle
@@ -393,7 +393,7 @@ int fun(int a)
int result = 0;
char *buffer = kmalloc(SIZE);

- if (buffer == NULL)
+ if (!buffer)
return -ENOMEM;

if (condition1) {
@@ -409,7 +409,36 @@ out:
return result;

- Chapter 8: Commenting
+ Chapyer 8: Tests
+Testing return values from function calls can get complex when you need
+to re-use the value later on. You should store the value before doing
+any tests on it. Never assign values inside a condition to another
+ err = test_something();
+ if (err) {
+ printk(KERN_ERR "Error: test_something() failed\n");
+ return err;
+ }
+If you give your variables and pointers good names, there is never a need
+to compare the value stored in that variable to NULL or true/false, so
+omit all that and keep it short.
+ ptr = s->next;
+ if (!ptr)
+ return;
+ v = (read_byte(register));
+ if (v & mask)
+ return;
+ if (is_prime(number))
+ return 0;
+ Chapter 9: Commenting

Comments are good, but there is also a danger of over-commenting. NEVER
try to explain HOW your code works in a comment: it's much better to
@@ -449,7 +478,7 @@ multiple data declarations). This leaves you room for a small comment on each
item, explaining its use.

- Chapter 9: You've made a mess of it
+ Chapter 10: You've made a mess of it

That's OK, we all do. You've probably been told by your long-time Unix
user helper that "GNU emacs" automatically formats the C sources for
@@ -497,7 +526,7 @@ re-formatting you may want to take a look at the man page. But
remember: "indent" is not a fix for bad programming.

- Chapter 10: Configuration-files
+ Chapter 11: Configuration-files

For configuration options (arch/xxx/Kconfig, and all the Kconfig files),
somewhat different indentation is used.
@@ -522,7 +551,7 @@ support for file-systems, for instance) should be denoted (DANGEROUS), other
experimental options should be denoted (EXPERIMENTAL).

- Chapter 11: Data structures
+ Chapter 12: Data structures

Data structures that have visibility outside the single-threaded
environment they are created and destroyed in should always have
@@ -553,7 +582,7 @@ Remember: if another thread can find your data structure, and you don't
have a reference count on it, you almost certainly have a bug.

- Chapter 12: Macros, Enums and RTL
+ Chapter 13: Macros, Enums and RTL

Names of macros defining constants and labels in enums are capitalized.

@@ -608,7 +637,7 @@ The cpp manual deals with macros exhaustively. The gcc internals manual also
covers RTL which is used frequently with assembly language in the kernel.

- Chapter 13: Printing kernel messages
+ Chapter 14: Printing kernel messages

Kernel developers like to be seen as literate. Do mind the spelling
of kernel messages to make a good impression. Do not use crippled
@@ -619,7 +648,7 @@ Kernel messages do not have to be terminated with a period.
Printing numbers in parentheses (%d) adds no value and should be avoided.

- Chapter 14: Allocating memory
+ Chapter 15: Allocating memory

The kernel provides the following general purpose memory allocators:
kmalloc(), kzalloc(), kcalloc(), and vmalloc(). Please refer to the API
@@ -638,7 +667,7 @@ from void pointer to any other pointer type is guaranteed by the C programming

- Chapter 15: The inline disease
+ Chapter 16: The inline disease

There appears to be a common misperception that gcc has a magic "make me
faster" speedup option called "inline". While the use of inlines can be
@@ -665,7 +694,7 @@ appears outweighs the potential value of the hint that tells gcc to do
something it would have done anyway.

- Chapter 16: Function return values and names
+ Chapter 17: Function return values and names

Functions can return values of many different kinds, and one of the
most common is a value indicating whether the function succeeded or
@@ -699,7 +728,7 @@ result. Typical examples would be functions that return pointers; they use
NULL or the ERR_PTR mechanism to report failure.

- Chapter 17: Don't re-invent the kernel macros
+ Chapter 18: Don't re-invent the kernel macros

The header file include/linux/kernel.h contains a number of macros that
you should use, rather than explicitly coding some variant of them yourself.
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