HACKING 30.5 KB
Newer Older
1
-*- buffer-read-only: t -*- vi: set ro:
2 3
DO NOT EDIT THIS FILE!  IT IS GENERATED AUTOMATICALLY
from docs/hacking.html.in!
4

5 6 7 8 9


                         Contributor guidelines
                         ======================

10 11


12 13
General tips for contributing patches
=====================================
14 15
(1) Discuss any large changes on the mailing list first. Post patches early and
listen to feedback.
16

E
Eric Blake 已提交
17 18 19 20 21 22
(2) Post patches in unified diff format, with git rename detection enabled. You
need a one-time setup of:

  git config diff.renames true

After that, a command similar to this should work:
23 24 25 26 27

  diff -urp libvirt.orig/ libvirt.modified/ > libvirt-myfeature.patch

or:

28
  git diff > libvirt-myfeature.patch
29

E
Eric Blake 已提交
30 31 32
Also, for code motion patches, you may find that "git diff --patience"
provides an easier-to-read patch. However, the usual workflow of libvirt
developer is:
33 34 35 36 37 38 39 40 41 42

  git checkout master
  git pull
  git checkout -t origin -b workbranch
  Hack, committing any changes along the way

Then, when you want to post your patches:

  git pull --rebase
  (fix any conflicts)
43 44
  git send-email --cover-letter --no-chain-reply-to --annotate \
                 --to=libvir-list@redhat.com master
45

46 47 48 49 50 51
(Note that the "git send-email" subcommand may not be in the main git package
and using it may require installion of a separate package, for example the
"git-email" package in Fedora.) For a single patch you can omit
"--cover-letter", but a series of two or more patches needs a cover letter. If
you get tired of typing "--to=libvir-list@redhat.com" designation you can set
it in git config:
52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67

  git config sendemail.to libvir-list@redhat.com

Please follow this as close as you can, especially the rebase and git
send-email part, as it makes life easier for other developers to review your
patch set. One should avoid sending patches as attachments, but rather send
them in email body along with commit message. If a developer is sending
another version of the patch (e.g. to address review comments), he is advised
to note differences to previous versions after the "---" line in the patch so
that it helps reviewers but doesn't become part of git history. Moreover, such
patch needs to be prefixed correctly with "--subject-prefix=PATCHv2" appended
to "git send-email" (substitute "v2" with the correct version if needed
though).



E
Eric Blake 已提交
68 69 70 71 72 73 74 75 76 77 78 79 80
(3) In your commit message, make the summary line reasonably short (60 characters
is typical), followed by a blank line, followed by any longer description of
why your patch makes sense. If the patch fixes a regression, and you know what
commit introduced the problem, mentioning that is useful. If the patch
resolves a bugzilla report, mentioning the URL of the bug number is useful;
but also summarize the issue rather than making all readers follow the link.
You can use 'git shortlog -30' to get an idea of typical summary lines.
Libvirt does not currently attach any meaning to Signed-off-by: lines, so it
is up to you if you want to include or omit them in the commit message.



(4) Split large changes into a series of smaller patches, self-contained if
81
possible, with an explanation of each patch and an explanation of how the
82
sequence of patches fits together. Moreover, please keep in mind that it's
83 84 85 86 87
required to be able to compile cleanly (*including* "make check" and "make
syntax-check") after each patch. A feature does not have to work until the end
of a series, but intermediate patches must compile and not cause test-suite
failures (this is to preserve the usefulness of "git bisect", among other
things).
88 89


90

E
Eric Blake 已提交
91
(5) Make sure your patches apply against libvirt GIT. Developers only follow GIT
92
and don't care much about released versions.
93

E
Eric Blake 已提交
94
(6) Run the automated tests on your code before submitting any changes. In
95 96
particular, configure with compile warnings set to -Werror. This is done
automatically for a git checkout; from a tarball, use:
97

98
  ./configure --enable-werror
99 100 101 102 103 104 105

and run the tests:

  make check
  make syntax-check
  make -C tests valgrind

106 107 108 109 110


  Valgrind
  http://valgrind.org/is a test that checks for memory management issues, such as leaks or use of
uninitialized variables.
111

112 113 114 115 116 117 118
If you encounter any failing tests, the VIR_TEST_DEBUG environment variable
may provide extra information to debug the failures. Larger values of
VIR_TEST_DEBUG may provide larger amounts of information:

  VIR_TEST_DEBUG=1 make check    (or)
  VIR_TEST_DEBUG=2 make check

119
Also, individual tests can be run from inside the "tests/" directory, like:
120 121 122

  ./qemuxml2xmltest

E
Eric Blake 已提交
123 124
There is also a "./run" script at the top level, to make it easier to run
programs that have not yet been installed, as well as to wrap invocations of
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
various tests under gdb or Valgrind.



(7) The Valgrind test should produce similar output to "make check". If the output
has traces within libvirt API's, then investigation is required in order to
determine the cause of the issue. Output such as the following indicates some
sort of leak:

==5414== 4 bytes in 1 blocks are definitely lost in loss record 3 of 89
==5414==    at 0x4A0881C: malloc (vg_replace_malloc.c:270)
==5414==    by 0x34DE0AAB85: xmlStrndup (in /usr/lib64/libxml2.so.2.7.8)
==5414==    by 0x4CC97A6: virDomainVideoDefParseXML (domain_conf.c:7410)
==5414==    by 0x4CD581D: virDomainDefParseXML (domain_conf.c:10188)
==5414==    by 0x4CD8C73: virDomainDefParseNode (domain_conf.c:10640)
==5414==    by 0x4CD8DDB: virDomainDefParse (domain_conf.c:10590)
==5414==    by 0x41CB1D: testCompareXMLToArgvHelper (qemuxml2argvtest.c:100)
==5414==    by 0x41E20F: virtTestRun (testutils.c:161)
==5414==    by 0x41C7CB: mymain (qemuxml2argvtest.c:866)
==5414==    by 0x41E84A: virtTestMain (testutils.c:723)
==5414==    by 0x34D9021734: (below main) (in /usr/lib64/libc-2.15.so)

In this example, the "virDomainDefParseXML()" had an error path where the
"virDomainVideoDefPtr video" pointer was not properly disposed. By simply
adding a "virDomainVideoDefFree(video);" in the error path, the issue was
resolved.

Another common mistake is calling a printing function, such as "VIR_DEBUG()"
without initializing a variable to be printed. The following example involved
a call which could return an error, but not set variables passed by reference
to the call. The solution was to initialize the variables prior to the call.

==4749== Use of uninitialised value of size 8
==4749==    at 0x34D904650B: _itoa_word (in /usr/lib64/libc-2.15.so)
==4749==    by 0x34D9049118: vfprintf (in /usr/lib64/libc-2.15.so)
==4749==    by 0x34D9108F60: __vasprintf_chk (in /usr/lib64/libc-2.15.so)
==4749==    by 0x4CAEEF7: virVasprintf (stdio2.h:199)
==4749==    by 0x4C8A55E: virLogVMessage (virlog.c:814)
==4749==    by 0x4C8AA96: virLogMessage (virlog.c:751)
==4749==    by 0x4DA0056: virNetTLSContextCheckCertKeyUsage (virnettlscontext.c:225)
==4749==    by 0x4DA06DB: virNetTLSContextCheckCert (virnettlscontext.c:439)
==4749==    by 0x4DA1620: virNetTLSContextNew (virnettlscontext.c:562)
==4749==    by 0x4DA26FC: virNetTLSContextNewServer (virnettlscontext.c:927)
==4749==    by 0x409C39: testTLSContextInit (virnettlscontexttest.c:467)
==4749==    by 0x40AB8F: virtTestRun (testutils.c:161)

Valgrind will also find some false positives or code paths which cannot be
resolved by making changes to the libvirt code. For these paths, it is
possible to add a filter to avoid the errors. For example:

==4643== 7 bytes in 1 blocks are possibly lost in loss record 4 of 20
==4643==    at 0x4A0881C: malloc (vg_replace_malloc.c:270)
==4643==    by 0x34D90853F1: strdup (in /usr/lib64/libc-2.15.so)
==4643==    by 0x34EEC2C08A: ??? (in /usr/lib64/libnl.so.1.1)
==4643==    by 0x34EEC15B81: ??? (in /usr/lib64/libnl.so.1.1)
==4643==    by 0x34D8C0EE15: call_init.part.0 (in /usr/lib64/ld-2.15.so)
==4643==    by 0x34D8C0EECF: _dl_init (in /usr/lib64/ld-2.15.so)
==4643==    by 0x34D8C01569: ??? (in /usr/lib64/ld-2.15.so)


In this instance, it is acceptible to modify the "tests/.valgrind.supp" file
in order to add a suppression filter. The filter should be unique enough to
not suppress real leaks, but it should be generic enough to cover multiple
code paths. The format of the entry can be found in the documentation found at
the

  Valgrind home page.
  http://valgrind.org/The following trace was added to "tests/.valgrind.supp" in order to suppress
the warning:

{
    dlInitMemoryLeak1
    Memcheck:Leak
    fun:?alloc
    ...
    fun:call_init.part.0
    fun:_dl_init
    ...
    obj:*/lib*/ld-2.*so*
}

206 207


208
(8) Update tests and/or documentation, particularly if you are adding a new
209
feature or changing the output of a program.
210 211


212

213 214
There is more on this subject, including lots of links to background reading
on the subject, on
215

216 217
  Richard Jones' guide to working with open source projects
  http://et.redhat.com/~rjones/how-to-supply-code-to-open-source-projects/
218

219

220 221 222
Code indentation
================
Libvirt's C source code generally adheres to some basic code-formatting
223 224 225 226
conventions. The existing code base is not totally consistent on this front,
but we do prefer that contributed code be formatted similarly. In short, use
spaces-not-TABs for indentation, use 4 spaces for each indentation level, and
other than that, follow the K&R style.
227 228 229 230 231 232 233 234 235 236 237 238 239

If you use Emacs, add the following to one of one of your start-up files
(e.g., ~/.emacs), to help ensure that you get indentation right:

  ;;; When editing C sources in libvirt, use this style.
  (defun libvirt-c-mode ()
    "C mode with adjusted defaults for use with libvirt."
    (interactive)
    (c-set-style "K&R")
    (setq indent-tabs-mode nil) ; indent using spaces, not TABs
    (setq c-indent-level 4)
    (setq c-basic-offset 4))
  (add-hook 'c-mode-hook
240 241 242
            '(lambda () (if (string-match "/libvirt" (buffer-file-name))
                            (libvirt-c-mode))))

243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264
If you use vim, append the following to your ~/.vimrc file:

  set nocompatible
  filetype on
  set autoindent
  set smartindent
  set cindent
  set tabstop=8
  set shiftwidth=4
  set expandtab
  set cinoptions=(0,:0,l1,t0
  filetype plugin indent on
  au FileType make setlocal noexpandtab
  au BufRead,BufNewFile *.am setlocal noexpandtab
  match ErrorMsg /\s\+$\| \+\ze\t/

Or if you don't want to mess your ~/.vimrc up, you can save the above into a
file called .lvimrc (not .vimrc) located at the root of libvirt source, then
install a vim script from
http://www.vim.org/scripts/script.php?script_id=1408, which will load the
.lvimrc only when you edit libvirt code.

265 266 267

Code formatting (especially for new code)
=========================================
268 269 270
With new code, we can be even more strict. Please apply the following function
(using GNU indent) to any new code. Note that this also gives you an idea of
the type of spacing we prefer around operators and keywords:
271 272 273 274 275 276 277 278

  indent-libvirt()
  {
    indent -bad -bap -bbb -bli4 -br -ce -brs -cs -i4 -l75 -lc75 \
      -sbi4 -psl -saf -sai -saw -sbi4 -ss -sc -cdw -cli4 -npcs -nbc \
      --no-tabs "$@"
  }

279 280 281
Note that sometimes you'll have to post-process that output further, by piping
it through "expand -i", since some leading TABs can get through. Usually
they're in macro definitions or strings, and should be converted anyhow.
282

283 284 285 286 287 288
Libvirt requires a C99 compiler for various reasons. However, most of the code
base prefers to stick to C89 syntax unless there is a compelling reason
otherwise. For example, it is preferable to use "/* */" comments rather than
"//". Also, when declaring local variables, the prevailing style has been to
declare them at the beginning of a scope, rather than immediately before use.

289

290 291 292
Bracket spacing
===============
The keywords "if", "for", "while", and "switch" must have a single space
M
Martin Kletzander 已提交
293
following them before the opening bracket. E.g.
294 295 296 297

      if(foo)   // Bad
      if (foo)  // Good

M
Martin Kletzander 已提交
298
Function implementations mustnothave any whitespace between the function name and the opening bracket. E.g.
299 300 301 302

      int foo (int wizz)  // Bad
      int foo(int wizz)   // Good

M
Martin Kletzander 已提交
303
Function calls mustnothave any whitespace between the function name and the opening bracket. E.g.
304 305 306 307 308

      bar = foo (wizz);  // Bad
      bar = foo(wizz);   // Good

Function typedefs mustnothave any whitespace between the closing bracket of the function name and
M
Martin Kletzander 已提交
309
opening bracket of the arg list. E.g.
310 311 312 313 314

      typedef int (*foo) (int wizz);  // Bad
      typedef int (*foo)(int wizz);   // Good

There must not be any whitespace immediately following any opening bracket, or
M
Martin Kletzander 已提交
315
immediately prior to any closing bracket. E.g.
316 317 318 319 320

      int foo( int wizz );  // Bad
      int foo(int wizz);    // Good


321 322 323 324
Curly braces
============
Omit the curly braces around an "if", "while", "for" etc. body only when that
body occupies a single line. In every other case we require the braces. This
325 326
ensures that it is trivially easy to identify a single-'statement' loop: each
has only one 'line' in its body.
327 328 329

Omitting braces with a single-line body is fine:

330 331
  while (expr) // one-line body -> omitting curly braces is ok
      single_line_stmt();
332

E
Eric Blake 已提交
333
However, the moment your loop/if/else body extends on to a second line, for
334 335
whatever reason (even if it's just an added comment), then you should add
braces. Otherwise, it would be too easy to insert a statement just before that
336
comment (without adding braces), thinking it is already a multi-statement loop:
337

338 339 340
  while (true) // BAD! multi-line body with no braces
      /* comment... */
      single_line_stmt();
341 342 343

Do this instead:

344 345 346 347
  while (true) { // Always put braces around a multi-line body.
      /* comment... */
      single_line_stmt();
  }
348 349 350 351

There is one exception: when the second body line is not at the same
indentation level as the first body line:

352 353 354
  if (expr)
      die("a diagnostic that would make this line"
          " extend past the 80-column limit"));
355 356 357 358 359 360

It is safe to omit the braces in the code above, since the further-indented
second body line makes it obvious that this is still a single-statement body.

To reiterate, don't do this:

361 362 363 364
  if (expr)            // BAD: no braces around...
      while (expr_2) { // ... a multi-line body
          ...
      }
365 366 367

Do this, instead:

368 369 370 371 372
  if (expr) {
      while (expr_2) {
          ...
      }
  }
373 374 375

However, there is one exception in the other direction, when even a one-line
block should have braces. That occurs when that one-line, brace-less block is
376 377 378 379 380
an "if" or "else" block, and the counterpart block *does* use braces. In that
case, put braces around both blocks. Also, if the "else" block is much shorter
than the "if" block, consider negating the "if"-condition and swapping the
bodies, putting the short block first and making the longer, multi-line block
be the "else" block.
381

382 383 384 385 386
  if (expr) {
      ...
      ...
  }
  else
387 388
      x = y;    // BAD: braceless "else" with braced "then",
                // and short block last
389

390 391 392 393 394 395
  if (expr)
      x = y;    // BAD: braceless "if" with braced "else"
  else {
      ...
      ...
  }
396

397 398 399 400 401 402
Keeping braces consistent and putting the short block first is preferred,
especially when the multi-line body is more than a few lines long, because it
is easier to read and grasp the semantics of an if-then-else block when the
simpler block occurs first, rather than after the more involved block:

  if (!expr) {
403
    x = y; // putting the smaller block first is more readable
404
  } else {
405 406 407
      ...
      ...
  }
408

409
But if negating a complex condition is too ugly, then at least add braces:
410

411
  if (complex expr not worth negating) {
412 413 414 415 416
      ...
      ...
  } else {
      x = y;
  }
417 418


419 420
Preprocessor
============
421 422 423 424 425
Macros defined with an ALL_CAPS name should generally be assumed to be unsafe
with regards to arguments with side-effects (that is, MAX(a++, b--) might
increment a or decrement b too many or too few times). Exceptions to this rule
are explicitly documented for macros in viralloc.h.

426 427
For variadic macros, stick with C99 syntax:

428
  #define vshPrint(_ctl, ...) fprintf(stdout, __VA_ARGS__)
429

430 431
Use parenthesis when checking if a macro is defined, and use indentation to
track nesting:
432

433 434 435
  #if defined(HAVE_POSIX_FALLOCATE) && !defined(HAVE_FALLOCATE)
  # define fallocate(a,ignored,b,c) posix_fallocate(a,b,c)
  #endif
436 437


438 439 440 441 442 443
C types
=======
Use the right type.

Scalars
-------
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
- If you're using "int" or "long", odds are good that there's a better type.

- If a variable is counting something, be sure to declare it with an unsigned
type.

- If it's memory-size-related, use "size_t" (use "ssize_t" only if required).

- If it's file-size related, use uintmax_t, or maybe "off_t".

- If it's file-offset related (i.e., signed), use "off_t".

- If it's just counting small numbers use "unsigned int"; (on all but oddball
embedded systems, you can assume that that type is at least four bytes wide).

- If a variable has boolean semantics, give it the "bool" type and use the
corresponding "true" and "false" macros. It's ok to include <stdbool.h>, since
libvirt's use of gnulib ensures that it exists and is usable.

- In the unusual event that you require a specific width, use a standard type
like "int32_t", "uint32_t", "uint64_t", etc.

- While using "bool" is good for readability, it comes with minor caveats:

-- Don't use "bool" in places where the type size must be constant across all
systems, like public interfaces and on-the-wire protocols. Note that it would
be possible (albeit wasteful) to use "bool" in libvirt's logical wire
protocol, since XDR maps that to its lower-level "bool_t" type, which *is*
fixed-size.

-- Don't compare a bool variable against the literal, "true", since a value with
a logical non-false value need not be "1". I.e., don't write "if (seen ==
true) ...". Rather, write "if (seen)...".





Of course, take all of the above with a grain of salt. If you're about to use
some system interface that requires a type like "size_t", "pid_t" or "off_t",
use matching types for any corresponding variables.

Also, if you try to use e.g., "unsigned int" as a type, and that conflicts
with the signedness of a related variable, sometimes it's best just to use the
*wrong* type, if 'pulling the thread' and fixing all related variables would
be too invasive.

Finally, while using descriptive types is important, be careful not to go
overboard. If whatever you're doing causes warnings, or requires casts, then
reconsider or ask for help.
493 494 495

Pointers
--------
496 497 498 499 500 501
Ensure that all of your pointers are 'const-correct'. Unless a pointer is used
to modify the pointed-to storage, give it the "const" attribute. That way, the
reader knows up-front that this is a read-only pointer. Perhaps more
importantly, if we're diligent about this, when you see a non-const pointer,
you're guaranteed that it is used to modify the storage it points to, or it is
aliased to another pointer that is.
502 503


504 505 506
Low level memory management
===========================
Use of the malloc/free/realloc/calloc APIs is deprecated in the libvirt
507 508
codebase, because they encourage a number of serious coding bugs and do not
enable compile time verification of checks for NULL. Instead of these
509
routines, use the macros from viralloc.h.
510

511
- To allocate a single object:
512

513 514 515 516 517 518
  virDomainPtr domain;

  if (VIR_ALLOC(domain) < 0) {
      virReportOOMError();
      return NULL;
  }
519 520 521



522
- To allocate an array of objects:
523

524
  virDomainPtr domains;
525
  size_t ndomains = 10;
526 527 528 529 530

  if (VIR_ALLOC_N(domains, ndomains) < 0) {
      virReportOOMError();
      return NULL;
  }
531 532 533



534
- To allocate an array of object pointers:
535

536
  virDomainPtr *domains;
537
  size_t ndomains = 10;
538

539 540 541 542 543 544 545
  if (VIR_ALLOC_N(domains, ndomains) < 0) {
      virReportOOMError();
      return NULL;
  }



546 547 548 549 550 551
- To re-allocate the array of domains to be 1 element longer (however, note that
repeatedly expanding an array by 1 scales quadratically, so this is
recommended only for smaller arrays):

  virDomainPtr domains;
  size_t ndomains = 0;
552

553
  if (VIR_EXPAND_N(domains, ndomains, 1) < 0) {
554 555 556
      virReportOOMError();
      return NULL;
  }
557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572
  domains[ndomains - 1] = domain;



- To ensure an array has room to hold at least one more element (this approach
scales better, but requires tracking allocation separately from usage)

  virDomainPtr domains;
  size_t ndomains = 0;
  size_t ndomains_max = 0;

  if (VIR_RESIZE_N(domains, ndomains_max, ndomains, 1) < 0) {
      virReportOOMError();
      return NULL;
  }
  domains[ndomains++] = domain;
573 574 575



576 577
- To trim an array of domains from its allocated size down to the actual used
size:
578

579 580 581 582
  virDomainPtr domains;
  size_t ndomains = x;
  size_t ndomains_max = y;

583
  VIR_SHRINK_N(domains, ndomains_max, ndomains_max - ndomains);
584 585 586



587
- To free an array of domains:
588

589 590 591 592 593 594 595 596 597
  virDomainPtr domains;
  size_t ndomains = x;
  size_t ndomains_max = y;
  size_t i;

  for (i = 0; i < ndomains; i++)
      VIR_FREE(domains[i]);
  VIR_FREE(domains);
  ndomains_max = ndomains = 0;
598 599 600 601 602 603






604 605
File handling
=============
606 607
Usage of the "fdopen()", "close()", "fclose()" APIs is deprecated in libvirt
code base to help avoiding double-closing of files or file descriptors, which
J
Ján Tomko 已提交
608
is particularly dangerous in a multi-threaded application. Instead of these
E
Eric Blake 已提交
609
APIs, use the macros from virfile.h
610

611
- Open a file from a file descriptor:
612 613 614 615 616 617 618 619 620

  if ((file = VIR_FDOPEN(fd, "r")) == NULL) {
      virReportSystemError(errno, "%s",
                           _("failed to open file from file descriptor"));
      return -1;
  }
  /* fd is now invalid; only access the file using file variable */


621

622
- Close a file descriptor:
623 624

  if (VIR_CLOSE(fd) < 0) {
625 626 627 628 629
      virReportSystemError(errno, "%s", _("failed to close file"));
  }



630
- Close a file:
631 632 633

  if (VIR_FCLOSE(file) < 0) {
      virReportSystemError(errno, "%s", _("failed to close file"));
634 635 636 637
  }



638 639
- Close a file or file descriptor in an error path, without losing the previous
"errno" value:
640 641

  VIR_FORCE_CLOSE(fd);
642
  VIR_FORCE_FCLOSE(file);
643 644


645 646 647



648 649 650

String comparisons
==================
651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666
Do not use the strcmp, strncmp, etc functions directly. Instead use one of the
following semantically named macros

- For strict equality:

  STREQ(a,b)
  STRNEQ(a,b)



- For case insensitive equality:

  STRCASEEQ(a,b)
  STRCASENEQ(a,b)


667

668
- For strict equality of a substring:
669

670 671
  STREQLEN(a,b,n)
  STRNEQLEN(a,b,n)
672 673 674



675
- For case insensitive equality of a substring:
676

677 678
  STRCASEEQLEN(a,b,n)
  STRCASENEQLEN(a,b,n)
679 680 681



682 683 684 685 686
- For strict equality of a prefix:

  STRPREFIX(a,b)


687

688 689 690 691 692 693 694
- To avoid having to check if a or b are NULL:

  STREQ_NULLABLE(a, b)
  STRNEQ_NULLABLE(a, b)



695 696 697



C
Chris Lalancette 已提交
698 699
String copying
==============
700 701 702
Do not use the strncpy function. According to the man page, it does *not*
guarantee a NULL-terminated buffer, which makes it extremely dangerous to use.
Instead, use one of the functionally equivalent functions:
C
Chris Lalancette 已提交
703

704
  virStrncpy(char *dest, const char *src, size_t n, size_t destbytes)
C
Chris Lalancette 已提交
705

706 707 708 709 710 711
The first three arguments have the same meaning as for strncpy; namely the
destination, source, and number of bytes to copy, respectively. The last
argument is the number of bytes available in the destination string; if a copy
of the source string (including a \0) will not fit into the destination, no
bytes are copied and the routine returns NULL. Otherwise, n bytes from the
source are copied into the destination and a trailing \0 is appended.
C
Chris Lalancette 已提交
712

713
  virStrcpy(char *dest, const char *src, size_t destbytes)
C
Chris Lalancette 已提交
714

715 716 717
Use this variant if you know you want to copy the entire src string into dest.
Note that this is a macro, so arguments could be evaluated more than once.
This is equivalent to virStrncpy(dest, src, strlen(src), destbytes)
C
Chris Lalancette 已提交
718

719 720 721 722 723 724 725
  virStrcpyStatic(char *dest, const char *src)

Use this variant if you know you want to copy the entire src string into dest
*and* you know that your destination string is a static string (i.e. that
sizeof(dest) returns something meaningful). Note that this is a macro, so
arguments could be evaluated more than once. This is equivalent to
virStrncpy(dest, src, strlen(src), sizeof(dest)).
C
Chris Lalancette 已提交
726

727 728 729 730 731 732 733 734 735 736 737
  VIR_STRDUP(char *dst, const char *src);
  VIR_STRNDUP(char *dst, const char *src, size_t n);

You should avoid using strdup or strndup directly as they do not report
out-of-memory error. Use VIR_STRDUP or VIR_STRNDUP macros instead. Note, that
these two behave similar to VIR_ALLOC: on success zero is returned, otherwise
the result is -1 and dst is guaranteed to be NULL. In very specific cases,
when you don't want to report the out-of-memory error, you can use
VIR_STRDUP_QUIET or VIR_STRNDUP_QUIET, but such usage is very rare and usually
considered a flaw.

C
Chris Lalancette 已提交
738

739 740
Variable length string buffer
=============================
741 742 743
If there is a need for complex string concatenations, avoid using the usual
sequence of malloc/strcpy/strcat/snprintf functions and make use of the
virBuffer API described in buf.h
744

745
Typical usage is as follows:
746 747

  char *
748 749
  somefunction(...)
  {
750 751 752 753 754
     virBuffer buf = VIR_BUFFER_INITIALIZER;

     ...

     virBufferAddLit(&buf, "<domain>\n");
755
     virBufferAsprintf(&buf, "  <memory>%d</memory>\n", memory);
756 757 758
     ...
     virBufferAddLit(&buf, "</domain>\n");

759
     ...
760 761

     if (virBufferError(&buf)) {
762
         virBufferFreeAndReset(&buf);
763
         virReportOOMError();
764 765 766 767 768
         return NULL;
     }

     return virBufferContentAndReset(&buf);
  }
769 770 771 772


Include files
=============
773 774 775
There are now quite a large number of include files, both libvirt internal and
external, and system includes. To manage all this complexity it's best to
stick to the following general plan for all *.c source files:
776 777 778 779 780 781 782 783 784 785 786 787 788 789 790

  /*
   * Copyright notice
   * ....
   * ....
   * ....
   *
   */

  #include <config.h>             Must come first in every file.

  #include <stdio.h>              Any system includes you need.
  #include <string.h>
  #include <limits.h>

791
  #if WITH_NUMACTL                Some system includes aren't supported
J
Jim Meyering 已提交
792
  # include <numa.h>              everywhere so need these #if guards.
793 794 795 796 797 798 799
  #endif

  #include "internal.h"           Include this first, after system includes.

  #include "util.h"               Any libvirt internal header files.
  #include "buf.h"

800 801
  static int
  myInternalFunc()                The actual code.
802
  {
803
      ...
804

O
Osier Yang 已提交
805 806 807 808 809 810
Of particular note: *Do not* include libvirt/libvirt.h, libvirt/virterror.h,
libvirt/libvirt-qemu.h, or libvirt/libvirt-lxc.h. They are included by
"internal.h" already and there are some special reasons why you cannot include
these files explicitly. One of the special cases, "libvirt/libvirt.h" is
included prior to "internal.h" in "remote_protocol.x", to avoid exposing
*_LAST enum elements.
811 812


813 814
Printf-style functions
======================
815 816 817 818 819 820 821 822 823 824 825
Whenever you add a new printf-style function, i.e., one with a format string
argument and following "..." in its prototype, be sure to use gcc's printf
attribute directive in the prototype. For example, here's the one for
virAsprintf, in util.h:

  int virAsprintf(char **strp, const char *fmt, ...)
      ATTRIBUTE_FORMAT(printf, 2, 3);

This makes it so gcc's -Wformat and -Wformat-security options can do their
jobs and cross-check format strings with the number and types of arguments.

E
Eric Blake 已提交
826 827 828 829 830 831
When printing to a string, consider using virBuffer for incremental
allocations, virAsprintf for a one-shot allocation, and snprintf for
fixed-width buffers. Do not use sprintf, even if you can prove the buffer
won't overflow, since gnulib does not provide the same portability guarantees
for sprintf as it does for snprintf.

832 833 834 835 836 837 838 839 840

Use of goto
===========
The use of goto is not forbidden, and goto is widely used throughout libvirt.
While the uncontrolled use of goto will quickly lead to unmaintainable code,
there is a place for it in well structured code where its use increases
readability and maintainability. In general, if goto is used for error
recovery, it's likely to be ok, otherwise, be cautious or avoid it all
together.
841

842 843 844 845 846 847 848 849 850
The typical use of goto is to jump to cleanup code in the case of a long list
of actions, any of which may fail and cause the entire operation to fail. In
this case, a function will have a single label at the end of the function.
It's almost always ok to use this style. In particular, if the cleanup code
only involves free'ing memory, then having multiple labels is overkill.
VIR_FREE() and every function named XXXFree() in libvirt is required to handle
NULL as its arg. Thus you can safely call free on all the variables even if
they were not yet allocated (yes they have to have been initialized to NULL).
This is much simpler and clearer than having multiple labels.
851

852
There are a couple of signs that a particular use of goto is not ok:
853

854 855 856
- You're using multiple labels. If you find yourself using multiple labels,
you're strongly encouraged to rework your code to eliminate all but one of
them.
857

858 859 860 861 862
- The goto jumps back up to a point above the current line of code being
executed. Please use some combination of looping constructs to re-execute code
instead; it's almost certainly going to be more understandable by others. One
well-known exception to this rule is restarting an i/o operation following
EINTR.
863

864 865 866 867
- The goto jumps down to an arbitrary place in the middle of a function followed
by further potentially failing calls. You should almost certainly be using a
conditional and a block instead of a goto. Perhaps some of your function's
logic would be better pulled out into a helper function.
868 869


870 871 872 873 874 875 876 877 878 879 880 881

Although libvirt does not encourage the Linux kernel wind/unwind style of
multiple labels, there's a good general discussion of the issue archived at

  KernelTrap
  http://kerneltrap.org/node/553/2131

When using goto, please use one of these standard labels if it makes sense:

      error: A path only taken upon return with an error code
    cleanup: A path taken upon return with success code + optional error
  no_memory: A path only taken upon return with an OOM error code
882
      retry: If needing to jump upwards (e.g., retry on EINTR)
883 884 885 886 887 888


Libvirt committer guidelines
============================
The AUTHORS files indicates the list of people with commit access right who
can actually merge the patches.
889

J
Jim Meyering 已提交
890
The general rule for committing a patch is to make sure it has been reviewed
891 892 893 894 895 896 897 898 899 900 901
properly in the mailing-list first, usually if a couple of people gave an ACK
or +1 to a patch and nobody raised an objection on the list it should be good
to go. If the patch touches a part of the code where you're not the main
maintainer, or where you do not have a very clear idea of how things work,
it's better to wait for a more authoritative feedback though. Before
committing, please also rebuild locally, run 'make check syntax-check', and
make sure you don't raise errors. Try to look for warnings too; for example,
configure with

  --enable-compile-warnings=error

902 903
which adds -Werror to compile flags, so no warnings get missed

904 905 906 907 908 909 910 911 912 913 914 915 916 917
An exception to 'review and approval on the list first' is fixing failures to
build:

- if a recently committed patch breaks compilation on a platform or for a given
driver, then it's fine to commit a minimal fix directly without getting the
review feedback first

- if make check or make syntax-check breaks, if there is an obvious fix, it's
fine to commit immediately. The patch should still be sent to the list (or
tell what the fix was if trivial), and 'make check syntax-check' should pass
too, before committing anything

- fixes for documentation and code comments can be managed in the same way, but
still make sure they get reviewed if non-trivial.