Kubos Coding and Documentation Standards

This is a doc to maintain the current naming and coding standards when working with the Kubos products.

Product Names

The general naming scheme for products is “Kubos {component}”. Note that there is a space separating the two words.

The component should be capitalized like a normal proper noun. First letter capitalized if the component is a word, all letters capitalized if the component is an initialism. For example:

  • Kubos Linux
  • Kubos SDK
  • Kubos CLI

KubOS (note the capitalization) refers to the entire system, not a specific component.

Component Names

Components within Kubos breakdown as follows:

  • API - a statically linked library
  • Service - A persistent process that is used to interact with the system. These typically utilize APIs.
  • Application - Makes decisions and uses the services.

Components added to the system should be referred to/labeled accordingly. See the Architecture Overview document for more information on each component’s roll.

File Naming

Code (*.c, *.h, scripts, etc)

  • No spaces
  • Use underscores to separate words
  • All lowercase

Docs (*.rst)

  • No spaces
  • Use hyphens to separate words
  • All lowercase


  • No spaces
  • Use hyphens to separate words
  • All lowercase

Special Files

The CONTRIUBUTING, LICENSE, and README files should all be uppercased.

‘Vagrantfile’, ‘Makefile’, ‘CMake’, and other similar files should all be cased to match industry standards.

Them’s Fightin’ Words

A few of the more controversial rules:

  • Spaces, not tabs
  • No if/for/while statements without brackets
  • All brackets on their own line
  • Use oxford commas
  • Single space after periods and colons

Documentation Standards

While creating clean and maintainable code is a high priority for our organization, writing successful documentation can be considered even more important. Documentation is a vital part of the user experience and, in most cases, will be a major component of a new customer’s first impression of us.

Each document should be concise and well-written, and should fill some logical gap missing from the current documentation set.

Our user docs are written using reStructuredText. This gives us a standardized way to construct and present user content.

Consider Your Audience

When writing a new document, consider who the expected reader is.

For a doc like “Installing the Kubos SDK”, we can assume that the reader is a brand new user. Therefore, few assumptions should be made about their current knowledge and, instead, the doc should have a great deal more handholding. This means more explicit explanations, more links to external resources, and more screenshots and example commands.

In contrast, with a doc like “Developing Kubos Modules” we can expect the reader to be a) familiar with our products and b) familiar with development in general. In this case, while handholding is still appreciated, the content can be more brief. Essential components are still fleshed out, but peripheral knowledge can be mentioned by simply linking to a relevant resource.


Headers should be considered the same as section titles. As a result, they should follow the same capitalization rules as titles. When in doubt, use this tool to check what should be capitalized.


The start of each document (and preferrably each high-level section) should have an overview blurb which describes what information the doc covers.

Some items to remember:

  • Single space after periods and colons
  • All commands which are not in a code block should be encased in backticks (`command`), rather than single or double quotes.
  • Use things like bullet points, bold or italicized text, and images to break up and highlight your content (no one likes a giant blob of text)
  • Oxford commas should always be used

Coding Standards

This section covers the styling and standards for the various languages and tools that we use.

C Standards

ClangFormat is a series of tools that can be used to automatically correct any C coding inconsistencies. A stand-alone tool is available, which can then be used with a variety of IDEs. We have created a ‘.clang-format’ file in the Kubos repo which can be used to automatically correct C code files to conform with our styling.

The following subsections are based on a doc generated 2017-04-18 by Coding Standard Generator version 1.13.


Each file must start with a copyright notice.

Header files must have a #pragma once statement. This causes the file to be included only once. If for some reason you encounter a scenario where the pragma statements are not supported, use include guards instead. The name used in the include guard should be the same name as the file (excluding the extension) followed by the suffix “_H”.


#pragma once


#ifndef FILE_H
#define FILE_H

System header files should be included with <> and project headers with “”.

Put all #include directives at the top of files. Having all #include directives in one place makes it easy to find them. Do not use absolute directory names in #include directives.

Put all #define statements immediately after any #include statements.

Put all function prototypes after any #define statements.


All functions should be fully documented in the header file that they belong to. Use the ‘/** ... */’ comment style so that Doxygen can add the function to the generated API documenation.

The function comment block should include: - A brief description of the function - The name, type, and purpose of all input variables - The name, type, and purpose of the returned value/s

For example:

 * Read data over i2c bus from specified address
 * In order to ensure safe i2c sharing, this function is semaphore locked.
 * There is one semaphore per bus. This function will block indefinitely
 * while waiting for the semaphore.
 * @param i2c i2c bus to read from
 * @param addr address of target i2c device
 * @param ptr pointer to data buffer
 * @param len length of data to read
 * @return int I2C_OK on success, I2C_ERROR on error
KI2CStatus k_i2c_read(KI2CNum i2c, uint16_t addr, uint8_t *ptr, int len);

For large and/or complex functions, it is helpful to also include the function comment block just above where the function is actually implemented. This way the developer can quickly review what the function is and how it’s supposed to work. The regular ‘/* ... */’ comment styling is acceptable in this case.

All code comments should be placed above the line the comment describes, indented identically, as opposed to allowing in-line comments.

/* comment here */
call_function(do, stuff) /* instead of here */

Code comments should cover the ‘what’ and ‘why’ of the following code, rather than the ‘how’.

Use #ifdef instead of /* ... */ to comment out blocks of code. The code that is commented out may already contain comments which then terminate the block comment and causes lots of compile errors or other harder to find errors.

However, code should not be left permanently commented out; “#ifdef 0” is fine when creating and testing code, but has no place in the final product. Make sure to remove all dead code before merging changes into the master branch.

Do not leave comments like ‘TODO’ or ‘FIX ME’ in your final code changes unless absolutely necessary. Just do whatever it is that you’re trying to procrastinate on. If you must leave a to-do, THERE BETTER BE A STORY FOR IT IN TRELLO AND IT BETTER BE AT THE TOP OF THE BACKLOG. “Oh, I’ll create a story for it later”. NO, YOU WON’T. DO IT NOW.


  • Constants, enumerators, and macros should be all upper case.
  • All other names should be all lower case.
  • Words should be separated by underscore (_).

Use sensible, descriptive names. Do not use short cryptic names or names based on internal jokes. It should be easy to type a name without looking up how it is spelt. Exception: Scratch variables used for temporary storage or indices are best kept short. A programmer reading such variables should be able to assume that its value is not used outside a few lines of code. Common scratch variables for integers are i, j, k, m, n and for characters c and d.

Use name prefixes for identifiers declared in different modules. For example, ‘csp_buffer_free’ indicates that the function belongs to the CSP directory.

Indentation and Spacing

Do not use tabs. Instead, use 4 spaces. Kubos developers and contributors use a variety of operating systems and development environments. Using spaces ensures that multiple people can contribute to the same file and all indentions will remain the same width, improving readability and cohesion.

Braces should follow “Exdented Style”.

The Exdented Bracing Style means that the curly brace pair are lined up with the surrounding statement. Statements and declarations between the braces are indented relative to the braces. Braces should be indented 4 columns to the right of the starting position of the enclosing statement or declaration.


void f(int a)
    int i;
    if (a > 0)
        i = a;
        i = a;

Loop and conditional statements (if, for, while) should always have brace enclosed sub-statements. The code looks more consistent if all conditional and loop statements have braces. Even if there is only a single statement after the condition or loop statement today, there might be a need for more code in the future.

Braces without any content may be placed on the same line.

while (...) {//do nothing};

Each statement should be placed on its own line. There is no need to make code compact. Putting several statements on the same line only makes the code cryptic to read.

Declare each variable in a separate declaration. This makes it easier to see all variables. It also avoids the problem of knowing which variables are pointers. int* p, i; It is easy to forget that the star belongs to the declared name, not the type, and look at this and say that the type is “pointer to int” and both p and i are declared to this type.

All binary arithmetic, bitwise and assignment operators and the ternary conditional operator (?:) should be surrounded by spaces; the comma operator should be followed by a space but not preceded. Exception: No spaces around pre/postfix increment and decrement operators (‘++’, ‘–’).

Loop and conditional statements should have a single space preceding the condition in parenthesis.

if (condition) /* correct */
if(condition)  /* wrong */

Lines should not exceed 78 characters. Even if your editor handles long lines, other people may have set up their editors differently. Long lines in the code may also cause problems for other programs and printers.


Provide names of parameters in function declarations. Parameter names are useful to document what the parameter is used for. The parameter names should be the same in all declarations and definitions of the function.

Always provide the return type explicitly.

Use a typedef to define a pointer to a function. Pointers to functions have a strange syntax. The code becomes much clearer if you use a typedef for the pointer to function type. This typedef name can then be used to declare variables etc.

double sin(double arg);
typedef double (*trig_func)(double arg);

/* Usage examples */
trig_func my_func = sin;
void call_func(trig_func callback);
trig_func func_table[10];

If not previously defined in a header file, declare variables as close to the first use as is useful. This is opposed to the old C requirement where all variables in a function needed to be declared before all instruction lines.

int doing_stuff(int parameter)

    /* declaring 'ret' here since it's needed for both cases */
    int ret = ALL_OK;

    if (condition)
        /* declaring 'val' here, since it's only used in this one case */
        int val = doing_things();
        ret = doing_things_with_val(val);
        ret = ERROR_CODE;

    return ret;


Never use gotos.

All switch statements should have a default label. Even if there is no action for the default label, it should be included to show that the programmer has considered values not covered by case labels. It is normally useful to place an error message in the default label in this case.

Return Values

In most cases, it is preferable to return an error code, rather than a value. If an output value is desired, a pointer to the desired storage area should be added to the function’s arguments. This allows us to be consistent in our declarations.

int length;
int ret;

/* Don't do this */
length = get_length(input);
/* Do this instead */
ret = get_length(input, length);

Other Typographical Issues

Avoid macros; most macros can be replaced by constants, enumerations or inline functions. Using macros can lead to decreased readability and increased chance of bugs.

Do not use literal numbers other than 0 and 1. Use constants instead of literal numbers to make the code consistent and easy to maintain. The name of the constant is also used to document the purpose of the number.

Do not rely on implicit conversion to bool in conditions.

if (ptr)         // wrong
if (ptr != NULL) // ok

Python Standards

Python’s PEP8 Style Guide is our preferred Python styling.

PyLint is a great tool which can be used to check the style and validity of your python files. It has support for a variety of editors and IDEs.

Autopep8 can be used to automatically format your code to conform with the Python PEP8 standard.

Rust Standards

The Rust code formatting RFCs are our preferred source for Rust styling.

rustfmt is our preferred tool for formatting code and enforcing these standards. It comes included in our SDK’s Vagrant box.

Working with External Projects

Some of the Kubos code uses or extends external projects. In this case where you are adding a new file, use the Kubos standards. If you are modifying an existing file, try to match the formatting of the surrounding code.

Linux Kernel

Linux kernel coding style


  • 8 space indentation
  • Torvalds disagrees with us on basically everything


U-Boot coding style


  • Mostly follows the Linux coding style
  • Tabs, not spaces
  • No C++ style comments (use /* */, not //)

Other Languages

Bash - Refer to Google’s style guide. Exception: Use 4 spaces, since that’s what we do in all of our other languages.