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Subject[PATCH] [condingstyle] Add chapter on tests

Based in part on Auke's patch.

Signed-off-by: Jan Engelhardt <>

Documentation/CodingStyle | 74 +++++++++++++++++++++++++++++++++++++++-------
1 file changed, 64 insertions(+), 10 deletions(-)

Index: linux-2.6.22-rc3/Documentation/CodingStyle
--- linux-2.6.22-rc3.orig/Documentation/CodingStyle
+++ linux-2.6.22-rc3/Documentation/CodingStyle
@@ -407,7 +407,61 @@ 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. Do not assign values inside a condition to another
+ err = test_something();
+ if (err) {
+ printk(KERN_ERR "Error: test_something() failed\n");
+ return err;
+ }
+Testing for a flag, as done in the following example, is redundant and
+can be shortened.
+ if ((v & GFP_KERNEL) == GFP_KERNEL)
+ return;
+should become
+ if (v & GFP_KERNEL)
+ return;
+The same goes for functions that return a bool:
+ if (is_prime(number) == true)
+ return 0;
+ if (is_prime(number) == false)
+ return 1;
+should be:
+ if (is_prime(number))
+ return 0;
+ if (!is_prime(number))
+ return 1;
+As far as pointers or functions returning an integer are concerned,
+using long form tests helps to distinguish between pointers and bools
+or functions returning boolean or integer, respectively.
+Examples are:
+ if (p == NULL)
+ return 1;
+ if (!p)
+ return 0;
+ if (strcmp(haystack, needle) == 0)
+ return 1;
+ if (!strcmp(haystack, needle))
+ 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
@@ -447,7 +501,7 @@ multiple data declarations). This leave
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
@@ -495,7 +549,7 @@ re-formatting you may want to take a loo
remember: "indent" is not a fix for bad programming.

- Chapter 10: Kconfig configuration files
+ Chapter 11: Kconfig configuration files

For all of the Kconfig* configuration files throughout the source tree,
the indentation is somewhat different. Lines under a "config" definition
@@ -531,7 +585,7 @@ For full documentation on the configurat

- 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
@@ -562,7 +616,7 @@ Remember: if another thread can find you
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.

@@ -617,7 +671,7 @@ The cpp manual deals with macros exhaust
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
@@ -628,7 +682,7 @@ Kernel messages do not have to be termin
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
@@ -647,7 +701,7 @@ from void pointer to any other pointer t

- 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
@@ -674,7 +728,7 @@ appears outweighs the potential value of
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
@@ -708,7 +762,7 @@ result. Typical examples would be funct
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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