--- /dev/null
+.. _coding_style:
+
+DPDK Coding Style
+=================
+
+Description
+-----------
+
+This document specifies the preferred style for source files in the DPDK source tree.
+It is based on the Linux Kernel coding guidelines and the FreeBSD 7.2 Kernel Developer's Manual (see man style(9)), but was heavily modified for the needs of the DPDK.
+
+General Guidelines
+------------------
+
+The rules and guidelines given in this document cannot cover every situation, so the following general guidelines should be used as a fallback:
+
+* The code style should be consistent within each individual file.
+* In the case of creating new files, the style should be consistent within each file in a given directory or module.
+* The primary reason for coding standards is to increase code readability and comprehensibility, therefore always use whatever option will make the code easiest to read.
+
+Line length is recommended to be not more than 80 characters, including comments.
+[Tab stop size should be assumed to be 8-characters wide].
+
+.. note::
+
+ The above is recommendation, and not a hard limit.
+ However, it is expected that the recommendations should be followed in all but the rarest situations.
+
+C Comment Style
+---------------
+
+Usual Comments
+~~~~~~~~~~~~~~
+
+These comments should be used in normal cases.
+To document a public API, a doxygen-like format must be used: refer to :ref:`doxygen_guidelines`.
+
+.. code-block:: c
+
+ /*
+ * VERY important single-line comments look like this.
+ */
+
+ /* Most single-line comments look like this. */
+
+ /*
+ * Multi-line comments look like this. Make them real sentences. Fill
+ * them so they look like real paragraphs.
+ */
+
+License Header
+~~~~~~~~~~~~~~
+
+Each file should begin with a special comment containing the appropriate copyright and license for the file.
+Generally this is the BSD License, except for code for Linux Kernel modules.
+After any copyright header, a blank line should be left before any other contents, e.g. include statements in a C file.
+
+C Preprocessor Directives
+-------------------------
+
+Header Includes
+~~~~~~~~~~~~~~~
+
+In DPDK sources, the include files should be ordered as following:
+
+#. libc includes (system includes first)
+#. DPDK EAL includes
+#. DPDK misc libraries includes
+#. application-specific includes
+
+Include files from the local application directory are included using quotes, while includes from other paths are included using angle brackets: "<>".
+
+Example:
+
+.. code-block:: c
+
+ #include <stdio.h>
+ #include <stdlib.h>
+
+ #include <rte_eal.h>
+
+ #include <rte_ring.h>
+ #include <rte_mempool.h>
+
+ #include "application.h"
+
+Header File Guards
+~~~~~~~~~~~~~~~~~~
+
+Headers should be protected against multiple inclusion with the usual:
+
+.. code-block:: c
+
+ #ifndef _FILE_H_
+ #define _FILE_H_
+
+ /* Code */
+
+ #endif /* _FILE_H_ */
+
+
+Macros
+~~~~~~
+
+Do not ``#define`` or declare names except with the standard DPDK prefix: ``RTE_``.
+This is to ensure there are no collisions with definitions in the application itself.
+
+The names of "unsafe" macros (ones that have side effects), and the names of macros for manifest constants, are all in uppercase.
+
+The expansions of expression-like macros are either a single token or have outer parentheses.
+If a macro is an inline expansion of a function, the function name is all in lowercase and the macro has the same name all in uppercase.
+If the macro encapsulates a compound statement, enclose it in a do-while loop, so that it can be used safely in if statements.
+Any final statement-terminating semicolon should be supplied by the macro invocation rather than the macro, to make parsing easier for pretty-printers and editors.
+
+For example:
+
+.. code-block:: c
+
+ #define MACRO(x, y) do { \
+ variable = (x) + (y); \
+ (y) += 2; \
+ } while(0)
+
+.. note::
+
+ Wherever possible, enums and inline functions should be preferred to macros, since they provide additional degrees of type-safety and can allow compilers to emit extra warnings about unsafe code.
+
+Conditional Compilation
+~~~~~~~~~~~~~~~~~~~~~~~
+
+* When code is conditionally compiled using ``#ifdef`` or ``#if``, a comment may be added following the matching
+ ``#endif`` or ``#else`` to permit the reader to easily discern where conditionally compiled code regions end.
+* This comment should be used only for (subjectively) long regions, regions greater than 20 lines, or where a series of nested ``#ifdef``'s may be confusing to the reader.
+ Exceptions may be made for cases where code is conditionally not compiled for the purposes of lint(1), or other tools, even though the uncompiled region may be small.
+* The comment should be separated from the ``#endif`` or ``#else`` by a single space.
+* For short conditionally compiled regions, a closing comment should not be used.
+* The comment for ``#endif`` should match the expression used in the corresponding ``#if`` or ``#ifdef``.
+* The comment for ``#else`` and ``#elif`` should match the inverse of the expression(s) used in the preceding ``#if`` and/or ``#elif`` statements.
+* In the comments, the subexpression ``defined(FOO)`` is abbreviated as "FOO".
+ For the purposes of comments, ``#ifndef FOO`` is treated as ``#if !defined(FOO)``.
+
+.. code-block:: c
+
+ #ifdef KTRACE
+ #include <sys/ktrace.h>
+ #endif
+
+ #ifdef COMPAT_43
+ /* A large region here, or other conditional code. */
+ #else /* !COMPAT_43 */
+ /* Or here. */
+ #endif /* COMPAT_43 */
+
+ #ifndef COMPAT_43
+ /* Yet another large region here, or other conditional code. */
+ #else /* COMPAT_43 */
+ /* Or here. */
+ #endif /* !COMPAT_43 */
+
+.. note::
+
+ Conditional compilation should be used only when absolutely necessary, as it increases the number of target binaries that need to be built and tested.
+
+C Types
+-------
+
+Integers
+~~~~~~~~
+
+For fixed/minimum-size integer values, the project uses the form uintXX_t (from stdint.h) instead of older BSD-style integer identifiers of the form u_intXX_t.
+
+Enumerations
+~~~~~~~~~~~~
+
+* Enumeration values are all uppercase.
+
+.. code-block:: c
+
+ enum enumtype { ONE, TWO } et;
+
+* Enum types should be used in preference to macros #defining a set of (sequential) values.
+* Enum types should be prefixed with ``rte_`` and the elements by a suitable prefix [generally starting ``RTE_<enum>_`` - where <enum> is a shortname for the enum type] to avoid namespace collisions.
+
+Bitfields
+~~~~~~~~~
+
+The developer should group bitfields that are included in the same integer, as follows:
+
+.. code-block:: c
+
+ struct grehdr {
+ uint16_t rec:3,
+ srr:1,
+ seq:1,
+ key:1,
+ routing:1,
+ csum:1,
+ version:3,
+ reserved:4,
+ ack:1;
+ /* ... */
+ }
+
+Variable Declarations
+~~~~~~~~~~~~~~~~~~~~~
+
+In declarations, do not put any whitespace between asterisks and adjacent tokens, except for tokens that are identifiers related to types.
+(These identifiers are the names of basic types, type qualifiers, and typedef-names other than the one being declared.)
+Separate these identifiers from asterisks using a single space.
+
+For example:
+
+.. code-block:: c
+
+ int *x; /* no space after asterisk */
+ int * const x; /* space after asterisk when using a type qualifier */
+
+* All externally-visible variables should have an ``rte_`` prefix in the name to avoid namespace collisions.
+* Do not use uppercase letters - either in the form of ALL_UPPERCASE, or CamelCase - in variable names.
+ Lower-case letters and underscores only.
+
+Structure Declarations
+~~~~~~~~~~~~~~~~~~~~~~
+
+* In general, when declaring variables in new structures, declare them sorted by use, then by size (largest to smallest), and then in alphabetical order.
+ Sorting by use means that commonly used variables are used together and that the structure layout makes logical sense.
+ Ordering by size then ensures that as little padding is added to the structure as possible.
+* For existing structures, additions to structures should be added to the end so for backward compatibility reasons.
+* Each structure element gets its own line.
+* Try to make the structure readable by aligning the member names using spaces as shown below.
+* Names following extremely long types, which therefore cannot be easily aligned with the rest, should be separated by a single space.
+
+.. code-block:: c
+
+ struct foo {
+ struct foo *next; /* List of active foo. */
+ struct mumble amumble; /* Comment for mumble. */
+ int bar; /* Try to align the comments. */
+ struct verylongtypename *baz; /* Won't fit with other members */
+ };
+
+
+* Major structures should be declared at the top of the file in which they are used, or in separate header files if they are used in multiple source files.
+* Use of the structures should be by separate variable declarations and those declarations must be extern if they are declared in a header file.
+* Externally visible structure definitions should have the structure name prefixed by ``rte_`` to avoid namespace collisions.
+
+Queues
+~~~~~~
+
+Use queue(3) macros rather than rolling your own lists, whenever possible.
+Thus, the previous example would be better written:
+
+.. code-block:: c
+
+ #include <sys/queue.h>
+
+ struct foo {
+ LIST_ENTRY(foo) link; /* Use queue macros for foo lists. */
+ struct mumble amumble; /* Comment for mumble. */
+ int bar; /* Try to align the comments. */
+ struct verylongtypename *baz; /* Won't fit with other members */
+ };
+ LIST_HEAD(, foo) foohead; /* Head of global foo list. */
+
+
+DPDK also provides an optimized way to store elements in lockless rings.
+This should be used in all data-path code, when there are several consumer and/or producers to avoid locking for concurrent access.
+
+Typedefs
+~~~~~~~~
+
+Avoid using typedefs for structure types.
+
+For example, use:
+
+.. code-block:: c
+
+ struct my_struct_type {
+ /* ... */
+ };
+
+ struct my_struct_type my_var;
+
+
+rather than:
+
+.. code-block:: c
+
+ typedef struct my_struct_type {
+ /* ... */
+ } my_struct_type;
+
+ my_struct_type my_var
+
+
+Typedefs are problematic because they do not properly hide their underlying type;
+for example, you need to know if the typedef is the structure itself, as shown above, or a pointer to the structure.
+In addition, they must be declared exactly once, whereas an incomplete structure type can be mentioned as many times as necessary.
+Typedefs are difficult to use in stand-alone header files.
+The header that defines the typedef must be included before the header that uses it, or by the header that uses it (which causes namespace pollution),
+or there must be a back-door mechanism for obtaining the typedef.
+
+Note that #defines used instead of typedefs also are problematic (since they do not propagate the pointer type correctly due to direct text replacement).
+For example, ``#define pint int *`` does not work as expected, while ``typedef int *pint`` does work.
+As stated when discussing macros, typedefs should be preferred to macros in cases like this.
+
+When convention requires a typedef; make its name match the struct tag.
+Avoid typedefs ending in ``_t``, except as specified in Standard C or by POSIX.
+
+.. note::
+
+ It is recommended to use typedefs to define function pointer types, for reasons of code readability.
+ This is especially true when the function type is used as a parameter to another function.
+
+For example:
+
+.. code-block:: c
+
+ /**
+ * Definition of a remote launch function.
+ */
+ typedef int (lcore_function_t)(void *);
+
+ /* launch a function of lcore_function_t type */
+ int rte_eal_remote_launch(lcore_function_t *f, void *arg, unsigned slave_id);
+
+
+C Indentation
+-------------
+
+General
+~~~~~~~
+
+* Indentation is a hard tab, that is, a tab character, not a sequence of spaces,
+
+.. note::
+
+ Global whitespace rule in DPDK, use tabs for indentation, spaces for alignment.
+
+* Do not put any spaces before a tab for indentation.
+* If you have to wrap a long statement, put the operator at the end of the line, and indent again.
+* For control statements (if, while, etc.), continuation it is recommended that the next line be indented by two tabs, rather than one,
+ to prevent confusion as to whether the second line of the control statement forms part of the statement body or not.
+ Alternatively, the line continuation may use additional spaces to line up to an appropriately point on the preceding line, for example, to align to an opening brace.
+
+.. note::
+
+ As with all style guidelines, code should match style already in use in an existing file.
+
+.. code-block:: c
+
+ while (really_long_variable_name_1 == really_long_variable_name_2 &&
+ var3 == var4){ /* confusing to read as */
+ x = y + z; /* control stmt body lines up with second line of */
+ a = b + c; /* control statement itself if single indent used */
+ }
+
+ if (really_long_variable_name_1 == really_long_variable_name_2 &&
+ var3 == var4){ /* two tabs used */
+ x = y + z; /* statement body no longer lines up */
+ a = b + c;
+ }
+
+ z = a + really + long + statement + that + needs +
+ two + lines + gets + indented + on + the +
+ second + and + subsequent + lines;
+
+
+* Do not add whitespace at the end of a line.
+
+* Do not add whitespace or a blank line at the end of a file.
+
+
+Control Statements and Loops
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+* Include a space after keywords (if, while, for, return, switch).
+* Do not use braces (``{`` and ``}``) for control statements with zero or just a single statement, unless that statement is more than a single line in which case the braces are permitted.
+
+.. code-block:: c
+
+ for (p = buf; *p != '\0'; ++p)
+ ; /* nothing */
+ for (;;)
+ stmt;
+ for (;;) {
+ z = a + really + long + statement + that + needs +
+ two + lines + gets + indented + on + the +
+ second + and + subsequent + lines;
+ }
+ for (;;) {
+ if (cond)
+ stmt;
+ }
+ if (val != NULL)
+ val = realloc(val, newsize);
+
+
+* Parts of a for loop may be left empty.
+
+.. code-block:: c
+
+ for (; cnt < 15; cnt++) {
+ stmt1;
+ stmt2;
+ }
+
+* Closing and opening braces go on the same line as the else keyword.
+* Braces that are not necessary should be left out.
+
+.. code-block:: c
+
+ if (test)
+ stmt;
+ else if (bar) {
+ stmt;
+ stmt;
+ } else
+ stmt;
+
+
+Function Calls
+~~~~~~~~~~~~~~
+
+* Do not use spaces after function names.
+* Commas should have a space after them.
+* No spaces after ``(`` or ``[`` or preceding the ``]`` or ``)`` characters.
+
+.. code-block:: c
+
+ error = function(a1, a2);
+ if (error != 0)
+ exit(error);
+
+
+Operators
+~~~~~~~~~
+
+* Unary operators do not require spaces, binary operators do.
+* Do not use parentheses unless they are required for precedence or unless the statement is confusing without them.
+ However, remember that other people may be more easily confused than you.
+
+Exit
+~~~~
+
+Exits should be 0 on success, or 1 on failure.
+
+.. code-block:: c
+
+ exit(0); /*
+ * Avoid obvious comments such as
+ * "Exit 0 on success."
+ */
+ }
+
+Local Variables
+~~~~~~~~~~~~~~~
+
+* Variables should be declared at the start of a block of code rather than in the middle.
+ The exception to this is when the variable is ``const`` in which case the declaration must be at the point of first use/assignment.
+* When declaring variables in functions, multiple variables per line are OK.
+ However, if multiple declarations would cause the line to exceed a reasonable line length, begin a new set of declarations on the next line rather than using a line continuation.
+* Be careful to not obfuscate the code by initializing variables in the declarations, only the last variable on a line should be initialized.
+ If multiple variables are to be initialized when defined, put one per line.
+* Do not use function calls in initializers, except for ``const`` variables.
+
+.. code-block:: c
+
+ int i = 0, j = 0, k = 0; /* bad, too many initializer */
+
+ char a = 0; /* OK, one variable per line with initializer */
+ char b = 0;
+
+ float x, y = 0.0; /* OK, only last variable has initializer */
+
+
+Casts and sizeof
+~~~~~~~~~~~~~~~~
+
+* Casts and sizeof statements are not followed by a space.
+* Always write sizeof statements with parenthesis.
+ The redundant parenthesis rules do not apply to sizeof(var) instances.
+
+C Function Definition, Declaration and Use
+-------------------------------------------
+
+Prototypes
+~~~~~~~~~~
+
+* It is recommended (and generally required by the compiler) that all non-static functions are prototyped somewhere.
+* Functions local to one source module should be declared static, and should not be prototyped unless absolutely necessary.
+* Functions used from other parts of code (external API) must be prototyped in the relevant include file.
+* Function prototypes should be listed in a logical order, preferably alphabetical unless there is a compelling reason to use a different ordering.
+* Functions that are used locally in more than one module go into a separate header file, for example, "extern.h".
+* Do not use the ``__P`` macro.
+* Functions that are part of an external API should be documented using Doxygen-like comments above declarations. See :ref:`doxygen_guidelines` for details.
+* Functions that are part of the external API must have an ``rte_`` prefix on the function name.
+* Do not use uppercase letters - either in the form of ALL_UPPERCASE, or CamelCase - in function names. Lower-case letters and underscores only.
+* When prototyping functions, associate names with parameter types, for example:
+
+.. code-block:: c
+
+ void function1(int fd); /* good */
+ void function2(int); /* bad */
+
+* Short function prototypes should be contained on a single line.
+ Longer prototypes, e.g. those with many parameters, can be split across multiple lines.
+ The second and subsequent lines should be further indented as for line statement continuations as described in the previous section.
+
+.. code-block:: c
+
+ static char *function1(int _arg, const char *_arg2,
+ struct foo *_arg3,
+ struct bar *_arg4,
+ struct baz *_arg5);
+ static void usage(void);
+
+.. note::
+
+ Unlike function definitions, the function prototypes do not need to place the function return type on a separate line.
+
+Definitions
+~~~~~~~~~~~
+
+* The function type should be on a line by itself preceding the function.
+* The opening brace of the function body should be on a line by itself.
+
+.. code-block:: c
+
+ static char *
+ function(int a1, int a2, float fl, int a4)
+ {
+
+
+* Do not declare functions inside other functions.
+ ANSI C states that such declarations have file scope regardless of the nesting of the declaration.
+ Hiding file declarations in what appears to be a local scope is undesirable and will elicit complaints from a good compiler.
+* Old-style (K&R) function declaration should not be used, use ANSI function declarations instead as shown below.
+* Long argument lists should be wrapped as described above in the function prototypes section.
+
+.. code-block:: c
+
+ /*
+ * All major routines should have a comment briefly describing what
+ * they do. The comment before the "main" routine should describe
+ * what the program does.
+ */
+ int
+ main(int argc, char *argv[])
+ {
+ char *ep;
+ long num;
+ int ch;
+
+C Statement Style and Conventions
+---------------------------------
+
+NULL Pointers
+~~~~~~~~~~~~~
+
+* NULL is the preferred null pointer constant.
+ Use NULL instead of ``(type *)0`` or ``(type *)NULL``, except where the compiler does not know the destination type e.g. for variadic args to a function.
+* Test pointers against NULL, for example, use:
+
+.. code-block:: c
+
+ if (p == NULL) /* Good, compare pointer to NULL */
+
+ if (!p) /* Bad, using ! on pointer */
+
+
+* Do not use ! for tests unless it is a boolean, for example, use:
+
+.. code-block:: c
+
+ if (*p == '\0') /* check character against (char)0 */
+
+Return Value
+~~~~~~~~~~~~
+
+* Functions which create objects, or allocate memory, should return pointer types, and NULL on error.
+ The error type should be indicated may setting the variable ``rte_errno`` appropriately.
+* Functions which work on bursts of packets, such as RX-like or TX-like functions, should return the number of packets handled.
+* Other functions returning int should generally behave like system calls:
+ returning 0 on success and -1 on error, setting ``rte_errno`` to indicate the specific type of error.
+* Where already standard in a given library, the alternative error approach may be used where the negative value is not -1 but is instead ``-errno`` if relevant, for example, ``-EINVAL``.
+ Note, however, to allow consistency across functions returning integer or pointer types, the previous approach is preferred for any new libraries.
+* For functions where no error is possible, the function type should be ``void`` not ``int``.
+* Routines returning ``void *`` should not have their return values cast to any pointer type.
+ (Typecasting can prevent the compiler from warning about missing prototypes as any implicit definition of a function returns int,
+ which, unlike ``void *``, needs a typecast to assign to a pointer variable.)
+
+.. note::
+
+ The above rule about not typecasting ``void *`` applies to malloc, as well as to DPDK functions.
+
+* Values in return statements should not be enclosed in parentheses.
+
+Logging and Errors
+~~~~~~~~~~~~~~~~~~
+
+In the DPDK environment, use the logging interface provided:
+
+.. code-block:: c
+
+ #define RTE_LOGTYPE_TESTAPP1 RTE_LOGTYPE_USER1
+ #define RTE_LOGTYPE_TESTAPP2 RTE_LOGTYPE_USER2
+
+ /* enable these logs type */
+ rte_set_log_type(RTE_LOGTYPE_TESTAPP1, 1);
+ rte_set_log_type(RTE_LOGTYPE_TESTAPP2, 1);
+
+ /* log in debug level */
+ rte_set_log_level(RTE_LOG_DEBUG);
+ RTE_LOG(DEBUG, TESTAPP1, "this is is a debug level message\n");
+ RTE_LOG(INFO, TESTAPP1, "this is is a info level message\n");
+ RTE_LOG(WARNING, TESTAPP1, "this is is a warning level message\n");
+
+ /* log in info level */
+ rte_set_log_level(RTE_LOG_INFO);
+ RTE_LOG(DEBUG, TESTAPP2, "debug level message (not displayed)\n");
+
+Branch Prediction
+~~~~~~~~~~~~~~~~~
+
+* When a test is done in a critical zone (called often or in a data path) the code can use the ``likely()`` and ``unlikely()`` macros to indicate the expected, or preferred fast path.
+ They are expanded as a compiler builtin and allow the developer to indicate if the branch is likely to be taken or not. Example:
+
+.. code-block:: c
+
+ #include <rte_branch_prediction.h>
+ if (likely(x > 1))
+ do_stuff();
+
+.. note::
+
+ The use of ``likely()`` and ``unlikely()`` should only be done in performance critical paths,
+ and only when there is a clearly preferred path, or a measured performance increase gained from doing so.
+ These macros should be avoided in non-performance-critical code.
+
+Static Variables and Functions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+* All functions and variables that are local to a file must be declared as ``static`` because it can often help the compiler to do some optimizations (such as, inlining the code).
+* Functions that should be inlined should to be declared as ``static inline`` and can be defined in a .c or a .h file.
+
+.. note::
+ Static functions defined in a header file must be declared as ``static inline`` in order to prevent compiler warnings about the function being unused.
+
+Const Attribute
+~~~~~~~~~~~~~~~
+
+The ``const`` attribute should be used as often as possible when a variable is read-only.
+
+Inline ASM in C code
+~~~~~~~~~~~~~~~~~~~~
+
+The ``asm`` and ``volatile`` keywords do not have underscores. The AT&T syntax should be used.
+Input and output operands should be named to avoid confusion, as shown in the following example:
+
+.. code-block:: c
+
+ asm volatile("outb %[val], %[port]"
+ : :
+ [port] "dN" (port),
+ [val] "a" (val));
+
+Control Statements
+~~~~~~~~~~~~~~~~~~
+
+* Forever loops are done with for statements, not while statements.
+* Elements in a switch statement that cascade should have a FALLTHROUGH comment. For example:
+
+.. code-block:: c
+
+ switch (ch) { /* Indent the switch. */
+ case 'a': /* Don't indent the case. */
+ aflag = 1; /* Indent case body one tab. */
+ /* FALLTHROUGH */
+ case 'b':
+ bflag = 1;
+ break;
+ case '?':
+ default:
+ usage();
+ /* NOTREACHED */
+ }
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