aboutsummaryrefslogtreecommitdiffstats
path: root/README.Coding
blob: 65d72d6fb735cc5274903f023833894183b096c3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
Coding conventions in the Samba tree
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. contents::

===========
Quick Start
===========

Coding style guidelines are about reducing the number of unnecessary
reformatting patches and making things easier for developers to work
together.
You don't have to like them or even agree with them, but once put in place
we all have to abide by them (or vote to change them).  However, coding
style should never outweigh coding itself and so the guidelines
described here are hopefully easy enough to follow as they are very
common and supported by tools and editors.

The basic style for C code is the Linux kernel coding style (See
Documentation/CodingStyle in the kernel source tree). This closely matches
what most Samba developers use already anyways, with a few exceptions as
mentioned below.

The coding style for Python code is documented in PEP8,
https://www.python.org/dev/peps/pep-0008/. New Python code should be compatible
with Python 2.6, 2.7, and Python 3.4 onwards. This means using Python 3 syntax
with the appropriate 'from __future__' imports.

But to save you the trouble of reading the Linux kernel style guide, here
are the highlights.

* Maximum Line Width is 80 Characters
  The reason is not about people with low-res screens but rather sticking
  to 80 columns prevents you from easily nesting more than one level of
  if statements or other code blocks.  Use source3/script/count_80_col.pl
  to check your changes.

* Use 8 Space Tabs to Indent
  No whitespace fillers.

* No Trailing Whitespace
  Use source3/script/strip_trail_ws.pl to clean up your files before
  committing.

* Follow the K&R guidelines.  We won't go through all of them here. Do you
  have a copy of "The C Programming Language" anyways right? You can also use
  the format_indent.sh script found in source3/script/ if all else fails.



============
Editor Hints
============

Emacs
-----
Add the follow to your $HOME/.emacs file:

  (add-hook 'c-mode-hook
	(lambda ()
		(c-set-style "linux")
		(c-toggle-auto-state)))


Vi
--
(Thanks to SATOH Fumiyasu <fumiyas@osstech.jp> for these hints):

For the basic vi editor included with all variants of \*nix, add the
following to $HOME/.exrc:

  set tabstop=8
  set shiftwidth=8

For Vim, the following settings in $HOME/.vimrc will also deal with
displaying trailing whitespace:

  if has("syntax") && (&t_Co > 2 || has("gui_running"))
	syntax on
	function! ActivateInvisibleCharIndicator()
		syntax match TrailingSpace "[ \t]\+$" display containedin=ALL
		highlight TrailingSpace ctermbg=Red
	endf
	autocmd BufNewFile,BufRead * call ActivateInvisibleCharIndicator()
  endif
  " Show tabs, trailing whitespace, and continued lines visually
  set list listchars=tab:»·,trail:·,extends:…

  " highlight overly long lines same as TODOs.
  set textwidth=80
  autocmd BufNewFile,BufRead *.c,*.h exec 'match Todo /\%>' . &textwidth . 'v.\+/'

clang-format
------------
BasedOnStyle: LLVM
IndentWidth: 8
UseTab: true
BreakBeforeBraces: Linux
AllowShortIfStatementsOnASingleLine: false
IndentCaseLabels: false
BinPackParameters: false
BinPackArguments: false
SortIncludes: false


=========================
FAQ & Statement Reference
=========================

Comments
--------

Comments should always use the standard C syntax.  C++
style comments are not currently allowed.

The lines before a comment should be empty. If the comment directly
belongs to the following code, there should be no empty line
after the comment, except if the comment contains a summary
of multiple following code blocks.

This is good:

	...
	int i;

	/*
	 * This is a multi line comment,
	 * which explains the logical steps we have to do:
	 *
	 * 1. We need to set i=5, because...
	 * 2. We need to call complex_fn1
	 */

	/* This is a one line comment about i = 5. */
	i = 5;

	/*
	 * This is a multi line comment,
	 * explaining the call to complex_fn1()
	 */
	ret = complex_fn1();
	if (ret != 0) {
	...

	/**
	 * @brief This is a doxygen comment.
	 *
	 * This is a more detailed explanation of
	 * this simple function.
	 *
	 * @param[in]   param1     The parameter value of the function.
	 *
	 * @param[out]  result1    The result value of the function.
	 *
	 * @return              0 on success and -1 on error.
	 */
	int example(int param1, int *result1);

This is bad:

	...
	int i;
	/*
	 * This is a multi line comment,
	 * which explains the logical steps we have to do:
	 *
	 * 1. We need to set i=5, because...
	 * 2. We need to call complex_fn1
	 */
	/* This is a one line comment about i = 5. */
	i = 5;
	/*
	 * This is a multi line comment,
	 * explaining the call to complex_fn1()
	 */
	ret = complex_fn1();
	if (ret != 0) {
	...

	/*This is a one line comment.*/

	/* This is a multi line comment,
	   with some more words...*/

	/*
	 * This is a multi line comment,
	 * with some more words...*/

Indention & Whitespace & 80 columns
-----------------------------------

To avoid confusion, indentations have to be tabs with length 8 (not 8
' ' characters).  When wrapping parameters for function calls,
align the parameter list with the first parameter on the previous line.
Use tabs to get as close as possible and then fill in the final 7
characters or less with whitespace.  For example,

	var1 = foo(arg1, arg2,
		   arg3);

The previous example is intended to illustrate alignment of function
parameters across lines and not as encourage for gratuitous line
splitting.  Never split a line before columns 70 - 79 unless you
have a really good reason. Be smart about formatting.

One exception to the previous rule is function calls, declarations, and
definitions. In function calls, declarations, and definitions, either the
declaration is a one-liner, or each parameter is listed on its own
line. The rationale is that if there are many parameters, each one
should be on its own line to make tracking interface changes easier.


If, switch, & Code blocks
-------------------------

Always follow an 'if' keyword with a space but don't include additional
spaces following or preceding the parentheses in the conditional.
This is good:

	if (x == 1)

This is bad:

	if ( x == 1 )

Yes we have a lot of code that uses the second form and we are trying
to clean it up without being overly intrusive.

Note that this is a rule about parentheses following keywords and not
functions.  Don't insert a space between the name and left parentheses when
invoking functions.

Braces for code blocks used by for, if, switch, while, do..while, etc.
should begin on the same line as the statement keyword and end on a line
of their own. You should always include braces, even if the block only
contains one statement.  NOTE: Functions are different and the beginning left
brace should be located in the first column on the next line.

If the beginning statement has to be broken across lines due to length,
the beginning brace should be on a line of its own.

The exception to the ending rule is when the closing brace is followed by
another language keyword such as else or the closing while in a do..while
loop.

Good examples:

	if (x == 1) {
		printf("good\n");
	}

	for (x=1; x<10; x++) {
		print("%d\n", x);
	}

	for (really_really_really_really_long_var_name=0;
	     really_really_really_really_long_var_name<10;
	     really_really_really_really_long_var_name++)
	{
		print("%d\n", really_really_really_really_long_var_name);
	}

	do {
		printf("also good\n");
	} while (1);

Bad examples:

	while (1)
	{
		print("I'm in a loop!\n"); }

	for (x=1;
	     x<10;
	     x++)
	{
		print("no good\n");
	}

	if (i < 10)
		print("I should be in braces.\n");


Goto
----

While many people have been academically taught that "goto"s are
fundamentally evil, they can greatly enhance readability and reduce memory
leaks when used as the single exit point from a function. But in no Samba
world what so ever is a goto outside of a function or block of code a good
idea.

Good Examples:

	int function foo(int y)
	{
		int *z = NULL;
		int ret = 0;

		if (y < 10) {
			z = malloc(sizeof(int) * y);
			if (z == NULL) {
				ret = 1;
				goto done;
			}
		}

		print("Allocated %d elements.\n", y);

	 done:
		if (z != NULL) {
			free(z);
		}

		return ret;
	}


Primitive Data Types
--------------------

Samba has large amounts of historical code which makes use of data types
commonly supported by the C99 standard. However, at the time such types
as boolean and exact width integers did not exist and Samba developers
were forced to provide their own.  Now that these types are guaranteed to
be available either as part of the compiler C99 support or from
lib/replace/, new code should adhere to the following conventions:

  * Booleans are of type "bool" (not BOOL)
  * Boolean values are "true" and "false" (not True or False)
  * Exact width integers are of type [u]int[8|16|32|64]_t

Most of the time a good name for a boolean variable is 'ok'. Here is an
example we often use:

	bool ok;

	ok = foo();
	if (!ok) {
		/* do something */
	}

It makes the code more readable and is easy to debug.

Typedefs
--------

Samba tries to avoid "typedef struct { .. } x_t;" so we do always try to use
"struct x { .. };". We know there are still such typedefs in the code,
but for new code, please don't do that anymore.

Initialize pointers
-------------------

All pointer variables MUST be initialized to NULL. History has
demonstrated that uninitialized pointer variables have lead to various
bugs and security issues.

Pointers MUST be initialized even if the assignment directly follows
the declaration, like pointer2 in the example below, because the
instructions sequence may change over time.

Good Example:

	char *pointer1 = NULL;
	char *pointer2 = NULL;

	pointer2 = some_func2();

	...

	pointer1 = some_func1();

Bad Example:

	char *pointer1;
	char *pointer2;

	pointer2 = some_func2();

	...

	pointer1 = some_func1();

Make use of helper variables
----------------------------

Please try to avoid passing function calls as function parameters
in new code. This makes the code much easier to read and
it's also easier to use the "step" command within gdb.

Good Example:

	char *name = NULL;
	int ret;

	name = get_some_name();
	if (name == NULL) {
		...
	}

	ret = some_function_my_name(name);
	...


Bad Example:

	ret = some_function_my_name(get_some_name());
	...

Please try to avoid passing function return values to if- or
while-conditions. The reason for this is better handling of code under a
debugger.

Good example:

	x = malloc(sizeof(short)*10);
	if (x == NULL) {
		fprintf(stderr, "Unable to alloc memory!\n");
	}

Bad example:

	if ((x = malloc(sizeof(short)*10)) == NULL ) {
		fprintf(stderr, "Unable to alloc memory!\n");
	}

There are exceptions to this rule. One example is walking a data structure in
an iterator style:

	while ((opt = poptGetNextOpt(pc)) != -1) {
		   ... do something with opt ...
	}

But in general, please try to avoid this pattern.


Control-Flow changing macros
----------------------------

Macros like NT_STATUS_NOT_OK_RETURN that change control flow
(return/goto/etc) from within the macro are considered bad, because
they look like function calls that never change control flow. Please
do not use them in new code.

The only exception is the test code that depends repeated use of calls
like CHECK_STATUS, CHECK_VAL and others.


Error and out logic
-------------------

Don't do this:

	frame = talloc_stackframe();

	if (ret == LDB_SUCCESS) {
		if (result->count == 0) {
			ret = LDB_ERR_NO_SUCH_OBJECT;
		} else {
			struct ldb_message *match =
				get_best_match(dn, result);
			if (match == NULL) {
				TALLOC_FREE(frame);
				return LDB_ERR_OPERATIONS_ERROR;
			}
			*msg = talloc_move(mem_ctx, &match);
		}
	}

	TALLOC_FREE(frame);
	return ret;

It should be:

	frame = talloc_stackframe();

	if (ret != LDB_SUCCESS) {
		TALLOC_FREE(frame);
		return ret;
	}

	if (result->count == 0) {
		TALLOC_FREE(frame);
		return LDB_ERR_NO_SUCH_OBJECT;
	}

	match = get_best_match(dn, result);
	if (match == NULL) {
		TALLOC_FREE(frame);
		return LDB_ERR_OPERATIONS_ERROR;
	}

	*msg = talloc_move(mem_ctx, &match);
	TALLOC_FREE(frame);
	return LDB_SUCCESS;


DEBUG statements
----------------

Use these following macros instead of DEBUG:

DBG_ERR	log level 0		error conditions
DBG_WARNING	log level 1		warning conditions
DBG_NOTICE	log level 3		normal, but significant, condition
DBG_INFO	log level 5		informational message
DBG_DEBUG	log level 10		debug-level message

Example usage:

DBG_ERR("Memory allocation failed\n");
DBG_DEBUG("Received %d bytes\n", count);

The messages from these macros are automatically prefixed with the
function name.