Open vSwitch Windows Datapath Coding Style

The coding style guide gives the flexiblity for each platform to use its own coding style for the kernel datapath. This file describes the specific coding style used in most of the C files in the Windows kernel datapath of the Open vSwitch distribution.

Most of the coding conventions applicable for the Open vSwitch distribution are applicable to the Windows kernel datapath as well. There are some exceptions and new guidlines owing to the commonly followed practices in Windows kernel/driver code. They are noted as follows:


  • Limit lines to 79 characters.

    Many times, this is not possible due to long names of functions and it is fine to go beyond the characters limit. One common example is when calling into NDIS functions.


Use data types defined by Windows for most of the code. This is a common practice in Windows driver code, and it makes integrating with the data structures and functions defined by Windows easier. Example: DWORD and BOOLEAN.

Use caution in portions of the code that interface with the OVS userspace. OVS userspace does not use Windows specific data types, and when copying data back and forth between kernel and userspace, care should be exercised.


It is common practice to use camel casing for naming variables, functions and files in Windows. For types, especially structures, unions and enums, using all upper case letters with words seprated by ‘_’ is common. These practices can be used for OVS Windows datapath. However, use the following guidelines:

  • Use lower case to begin the name of a variable.
  • Do not use ‘_’ to begin the name of the variable. ‘_’ is to be used to begin the parameters of a pre-processor macro.
  • Use upper case to begin the name of a function, enum, file name etc.
  • Static functions whose scope is limited to the file they are defined in can be prefixed with ‘_’. This is not mandatory though.
  • For types, use all upper case for all letters with words separated by ‘_’. If camel casing is preferred, use upper case for the first letter.
  • It is a common practice to define a pointer type by prefixing the letter ‘P’ to a data type. The same practice can be followed here as well.

For example:

static __inline BOOLEAN
                     POVS_FLOW_KEY flowKey)
    POVS_VPORT_ENTRY tunnelVport = NULL;

    if (!flowKey->ipKey.nwFrag &&
        flowKey->ipKey.nwProto == IPPROTO_UDP &&
        flowKey->ipKey.l4.tpDst == VXLAN_UDP_PORT_NBO) {
        tunnelVport = OvsGetTunnelVport(OVSWIN_VPORT_TYPE_VXLAN);
    } else {
        return FALSE;

    if (tunnelVport) {
        ASSERT(ovsFwdCtx->tunnelRxNic == NULL);
        ovsFwdCtx->tunnelRxNic = tunnelVport;
        return TRUE;

    return FALSE;

For declaring variables of pointer type, use of the pointer data type prefixed with ‘P’ is preferred over using ‘*’. This is not mandatory though, and is only prescribed since it is a common practice in Windows.

Example, #1 is preferred over #2 though #2 is also equally correct:

  2. NET_BUFFER_LIST *curNbl;


Comments should be written as full sentences that start with a capital letter and end with a period. Putting two spaces between sentances is not necessary.

// can be used for comments as long as the comment is a single line comment. For block comments, use /* */ comments


Put the return type, function name, and the braces that surround the function’s code on separate lines, all starting in column 0.

Before each function definition, write a comment that describes the function’s purpose, including each parameter, the return value, and side effects. References to argument names should be given in single-quotes, e.g. ‘arg’. The comment should not include the function name, nor need it follow any formal structure. The comment does not need to describe how a function does its work, unless this information is needed to use the function correctly (this is often better done with comments inside the function).

Mention any side effects that the function has that are not obvious based on the name of the function or based on the workflow it is called from.

In the interest of keeping comments describing functions similar in structure, use the following template.

 * Any description of the function, arguments, return types, assumptions and
 * side effects.

Source Files

Each source file should state its license in a comment at the very top, followed by a comment explaining the purpose of the code that is in that file. The comment should explain how the code in the file relates to code in other files. The goal is to allow a programmer to quickly figure out where a given module fits into the larger system.

The first non-comment line in a .c source file should be:

#include <precomp.h>

#include directives should appear in the following order:

  1. #include <precomp.h>
  2. The module’s own headers, if any. Including this before any other header (besides <precomp.h>) ensures that the module’s header file is self-contained (see Header Files) below.
  3. Standard C library headers and other system headers, preferably in alphabetical order. (Occasionally one encounters a set of system headers that must be included in a particular order, in which case that order must take precedence.)
  4. Open vSwitch headers, in alphabetical order. Use "", not <>, to specify Open vSwitch header names.