wrapper.c

   1 /*
   2  * Various trivial helper wrappers around standard functions
   3  */
   4 #include "git-compat-util.h"
   5 #include "abspath.h"
   6 #include "config.h"
   7 #include "gettext.h"
   8 #include "object.h"
   9 #include "repository.h"
  10 #include "strbuf.h"
  11 #include "trace2.h"
  12
  13 static intmax_t count_fsync_writeout_only;
  14 static intmax_t count_fsync_hardware_flush;
  15
  16 #ifdef HAVE_RTLGENRANDOM
  17 /* This is required to get access to RtlGenRandom. */
  18 #define SystemFunction036 NTAPI SystemFunction036
  19 #include <NTSecAPI.h>
  20 #undef SystemFunction036
  21 #endif
  22
  23 static int memory_limit_check(size_t size, int gentle)
  24 {
  25         static size_t limit = 0;
  26         if (!limit) {
  27                 limit = git_env_ulong("GIT_ALLOC_LIMIT", 0);
  28                 if (!limit)
  29                         limit = SIZE_MAX;
  30         }
  31         if (size > limit) {
  32                 if (gentle) {
  33                         error("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
  34                               (uintmax_t)size, (uintmax_t)limit);
  35                         return -1;
  36                 } else
  37                         die("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
  38                             (uintmax_t)size, (uintmax_t)limit);
  39         }
  40         return 0;
  41 }
  42
  43 char *xstrdup(const char *str)
  44 {
  45         char *ret = strdup(str);
  46         if (!ret)
  47                 die("Out of memory, strdup failed");
  48         return ret;
  49 }
  50
  51 static void *do_xmalloc(size_t size, int gentle)
  52 {
  53         void *ret;
  54
  55         if (memory_limit_check(size, gentle))
  56                 return NULL;
  57         ret = malloc(size);
  58         if (!ret && !size)
  59                 ret = malloc(1);
  60         if (!ret) {
  61                 if (!gentle)
  62                         die("Out of memory, malloc failed (tried to allocate %lu bytes)",
  63                             (unsigned long)size);
  64                 else {
  65                         error("Out of memory, malloc failed (tried to allocate %lu bytes)",
  66                               (unsigned long)size);
  67                         return NULL;
  68                 }
  69         }
  70 #ifdef XMALLOC_POISON
  71         memset(ret, 0xA5, size);
  72 #endif
  73         return ret;
  74 }
  75
  76 void *xmalloc(size_t size)
  77 {
  78         return do_xmalloc(size, 0);
  79 }
  80
  81 static void *do_xmallocz(size_t size, int gentle)
  82 {
  83         void *ret;
  84         if (unsigned_add_overflows(size, 1)) {
  85                 if (gentle) {
  86                         error("Data too large to fit into virtual memory space.");
  87                         return NULL;
  88                 } else
  89                         die("Data too large to fit into virtual memory space.");
  90         }
  91         ret = do_xmalloc(size + 1, gentle);
  92         if (ret)
  93                 ((char*)ret)[size] = 0;
  94         return ret;
  95 }
  96
  97 void *xmallocz(size_t size)
  98 {
  99         return do_xmallocz(size, 0);
 100 }
 101
 102 void *xmallocz_gently(size_t size)
 103 {
 104         return do_xmallocz(size, 1);
 105 }
 106
 107 /*
 108  * xmemdupz() allocates (len + 1) bytes of memory, duplicates "len" bytes of
 109  * "data" to the allocated memory, zero terminates the allocated memory,
 110  * and returns a pointer to the allocated memory. If the allocation fails,
 111  * the program dies.
 112  */
 113 void *xmemdupz(const void *data, size_t len)
 114 {
 115         return memcpy(xmallocz(len), data, len);
 116 }
 117
 118 char *xstrndup(const char *str, size_t len)
 119 {
 120         char *p = memchr(str, '\0', len);
 121         return xmemdupz(str, p ? p - str : len);
 122 }
 123
 124 int xstrncmpz(const char *s, const char *t, size_t len)
 125 {
 126         int res = strncmp(s, t, len);
 127         if (res)
 128                 return res;
 129         return s[len] == '\0' ? 0 : 1;
 130 }
 131
 132 void *xrealloc(void *ptr, size_t size)
 133 {
 134         void *ret;
 135
 136         if (!size) {
 137                 free(ptr);
 138                 return xmalloc(0);
 139         }
 140
 141         memory_limit_check(size, 0);
 142         ret = realloc(ptr, size);
 143         if (!ret)
 144                 die("Out of memory, realloc failed");
 145         return ret;
 146 }
 147
 148 void *xcalloc(size_t nmemb, size_t size)
 149 {
 150         void *ret;
 151
 152         if (unsigned_mult_overflows(nmemb, size))
 153                 die("data too large to fit into virtual memory space");
 154
 155         memory_limit_check(size * nmemb, 0);
 156         ret = calloc(nmemb, size);
 157         if (!ret && (!nmemb || !size))
 158                 ret = calloc(1, 1);
 159         if (!ret)
 160                 die("Out of memory, calloc failed");
 161         return ret;
 162 }
 163
 164 void xsetenv(const char *name, const char *value, int overwrite)
 165 {
 166         if (setenv(name, value, overwrite))
 167                 die_errno(_("could not setenv '%s'"), name ? name : "(null)");
 168 }
 169
 170 /**
 171  * xopen() is the same as open(), but it die()s if the open() fails.
 172  */
 173 int xopen(const char *path, int oflag, ...)
 174 {
 175         mode_t mode = 0;
 176         va_list ap;
 177
 178         /*
 179          * va_arg() will have undefined behavior if the specified type is not
 180          * compatible with the argument type. Since integers are promoted to
 181          * ints, we fetch the next argument as an int, and then cast it to a
 182          * mode_t to avoid undefined behavior.
 183          */
 184         va_start(ap, oflag);
 185         if (oflag & O_CREAT)
 186                 mode = va_arg(ap, int);
 187         va_end(ap);
 188
 189         for (;;) {
 190                 int fd = open(path, oflag, mode);
 191                 if (fd >= 0)
 192                         return fd;
 193                 if (errno == EINTR)
 194                         continue;
 195
 196                 if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
 197                         die_errno(_("unable to create '%s'"), path);
 198                 else if ((oflag & O_RDWR) == O_RDWR)
 199                         die_errno(_("could not open '%s' for reading and writing"), path);
 200                 else if ((oflag & O_WRONLY) == O_WRONLY)
 201                         die_errno(_("could not open '%s' for writing"), path);
 202                 else
 203                         die_errno(_("could not open '%s' for reading"), path);
 204         }
 205 }
 206
 207 static int handle_nonblock(int fd, short poll_events, int err)
 208 {
 209         struct pollfd pfd;
 210
 211         if (err != EAGAIN && err != EWOULDBLOCK)
 212                 return 0;
 213
 214         pfd.fd = fd;
 215         pfd.events = poll_events;
 216
 217         /*
 218          * no need to check for errors, here;
 219          * a subsequent read/write will detect unrecoverable errors
 220          */
 221         poll(&pfd, 1, -1);
 222         return 1;
 223 }
 224
 225 /*
 226  * xread() is the same a read(), but it automatically restarts read()
 227  * operations with a recoverable error (EAGAIN and EINTR). xread()
 228  * DOES NOT GUARANTEE that "len" bytes is read even if the data is available.
 229  */
 230 ssize_t xread(int fd, void *buf, size_t len)
 231 {
 232         ssize_t nr;
 233         if (len > MAX_IO_SIZE)
 234                 len = MAX_IO_SIZE;
 235         while (1) {
 236                 nr = read(fd, buf, len);
 237                 if (nr < 0) {
 238                         if (errno == EINTR)
 239                                 continue;
 240                         if (handle_nonblock(fd, POLLIN, errno))
 241                                 continue;
 242                 }
 243                 return nr;
 244         }
 245 }
 246
 247 /*
 248  * xwrite() is the same a write(), but it automatically restarts write()
 249  * operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
 250  * GUARANTEE that "len" bytes is written even if the operation is successful.
 251  */
 252 ssize_t xwrite(int fd, const void *buf, size_t len)
 253 {
 254         ssize_t nr;
 255         if (len > MAX_IO_SIZE)
 256                 len = MAX_IO_SIZE;
 257         while (1) {
 258                 nr = write(fd, buf, len);
 259                 if (nr < 0) {
 260                         if (errno == EINTR)
 261                                 continue;
 262                         if (handle_nonblock(fd, POLLOUT, errno))
 263                                 continue;
 264                 }
 265
 266                 return nr;
 267         }
 268 }
 269
 270 /*
 271  * xpread() is the same as pread(), but it automatically restarts pread()
 272  * operations with a recoverable error (EAGAIN and EINTR). xpread() DOES
 273  * NOT GUARANTEE that "len" bytes is read even if the data is available.
 274  */
 275 ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
 276 {
 277         ssize_t nr;
 278         if (len > MAX_IO_SIZE)
 279                 len = MAX_IO_SIZE;
 280         while (1) {
 281                 nr = pread(fd, buf, len, offset);
 282                 if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
 283                         continue;
 284                 return nr;
 285         }
 286 }
 287
 288 ssize_t read_in_full(int fd, void *buf, size_t count)
 289 {
 290         char *p = buf;
 291         ssize_t total = 0;
 292
 293         while (count > 0) {
 294                 ssize_t loaded = xread(fd, p, count);
 295                 if (loaded < 0)
 296                         return -1;
 297                 if (loaded == 0)
 298                         return total;
 299                 count -= loaded;
 300                 p += loaded;
 301                 total += loaded;
 302         }
 303
 304         return total;
 305 }
 306
 307 ssize_t write_in_full(int fd, const void *buf, size_t count)
 308 {
 309         const char *p = buf;
 310         ssize_t total = 0;
 311
 312         while (count > 0) {
 313                 ssize_t written = xwrite(fd, p, count);
 314                 if (written < 0)
 315                         return -1;
 316                 if (!written) {
 317                         errno = ENOSPC;
 318                         return -1;
 319                 }
 320                 count -= written;
 321                 p += written;
 322                 total += written;
 323         }
 324
 325         return total;
 326 }
 327
 328 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset)
 329 {
 330         char *p = buf;
 331         ssize_t total = 0;
 332
 333         while (count > 0) {
 334                 ssize_t loaded = xpread(fd, p, count, offset);
 335                 if (loaded < 0)
 336                         return -1;
 337                 if (loaded == 0)
 338                         return total;
 339                 count -= loaded;
 340                 p += loaded;
 341                 total += loaded;
 342                 offset += loaded;
 343         }
 344
 345         return total;
 346 }
 347
 348 int xdup(int fd)
 349 {
 350         int ret = dup(fd);
 351         if (ret < 0)
 352                 die_errno("dup failed");
 353         return ret;
 354 }
 355
 356 /**
 357  * xfopen() is the same as fopen(), but it die()s if the fopen() fails.
 358  */
 359 FILE *xfopen(const char *path, const char *mode)
 360 {
 361         for (;;) {
 362                 FILE *fp = fopen(path, mode);
 363                 if (fp)
 364                         return fp;
 365                 if (errno == EINTR)
 366                         continue;
 367
 368                 if (*mode && mode[1] == '+')
 369                         die_errno(_("could not open '%s' for reading and writing"), path);
 370                 else if (*mode == 'w' || *mode == 'a')
 371                         die_errno(_("could not open '%s' for writing"), path);
 372                 else
 373                         die_errno(_("could not open '%s' for reading"), path);
 374         }
 375 }
 376
 377 FILE *xfdopen(int fd, const char *mode)
 378 {
 379         FILE *stream = fdopen(fd, mode);
 380         if (!stream)
 381                 die_errno("Out of memory? fdopen failed");
 382         return stream;
 383 }
 384
 385 FILE *fopen_for_writing(const char *path)
 386 {
 387         FILE *ret = fopen(path, "w");
 388
 389         if (!ret && errno == EPERM) {
 390                 if (!unlink(path))
 391                         ret = fopen(path, "w");
 392                 else
 393                         errno = EPERM;
 394         }
 395         return ret;
 396 }
 397
 398 static void warn_on_inaccessible(const char *path)
 399 {
 400         warning_errno(_("unable to access '%s'"), path);
 401 }
 402
 403 int warn_on_fopen_errors(const char *path)
 404 {
 405         if (errno != ENOENT && errno != ENOTDIR) {
 406                 warn_on_inaccessible(path);
 407                 return -1;
 408         }
 409
 410         return 0;
 411 }
 412
 413 FILE *fopen_or_warn(const char *path, const char *mode)
 414 {
 415         FILE *fp = fopen(path, mode);
 416
 417         if (fp)
 418                 return fp;
 419
 420         warn_on_fopen_errors(path);
 421         return NULL;
 422 }
 423
 424 int xmkstemp(char *filename_template)
 425 {
 426         int fd;
 427         char origtemplate[PATH_MAX];
 428         strlcpy(origtemplate, filename_template, sizeof(origtemplate));
 429
 430         fd = mkstemp(filename_template);
 431         if (fd < 0) {
 432                 int saved_errno = errno;
 433                 const char *nonrelative_template;
 434
 435                 if (strlen(filename_template) != strlen(origtemplate))
 436                         filename_template = origtemplate;
 437
 438                 nonrelative_template = absolute_path(filename_template);
 439                 errno = saved_errno;
 440                 die_errno("Unable to create temporary file '%s'",
 441                         nonrelative_template);
 442         }
 443         return fd;
 444 }
 445
 446 /* Adapted from libiberty's mkstemp.c. */
 447
 448 #undef TMP_MAX
 449 #define TMP_MAX 16384
 450
 451 int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 452 {
 453         static const char letters[] =
 454                 "abcdefghijklmnopqrstuvwxyz"
 455                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 456                 "0123456789";
 457         static const int num_letters = ARRAY_SIZE(letters) - 1;
 458         static const char x_pattern[] = "XXXXXX";
 459         static const int num_x = ARRAY_SIZE(x_pattern) - 1;
 460         char *filename_template;
 461         size_t len;
 462         int fd, count;
 463
 464         len = strlen(pattern);
 465
 466         if (len < num_x + suffix_len) {
 467                 errno = EINVAL;
 468                 return -1;
 469         }
 470
 471         if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) {
 472                 errno = EINVAL;
 473                 return -1;
 474         }
 475
 476         /*
 477          * Replace pattern's XXXXXX characters with randomness.
 478          * Try TMP_MAX different filenames.
 479          */
 480         filename_template = &pattern[len - num_x - suffix_len];
 481         for (count = 0; count < TMP_MAX; ++count) {
 482                 int i;
 483                 uint64_t v;
 484                 if (csprng_bytes(&v, sizeof(v)) < 0)
 485                         return error_errno("unable to get random bytes for temporary file");
 486
 487                 /* Fill in the random bits. */
 488                 for (i = 0; i < num_x; i++) {
 489                         filename_template[i] = letters[v % num_letters];
 490                         v /= num_letters;
 491                 }
 492
 493                 fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
 494                 if (fd >= 0)
 495                         return fd;
 496                 /*
 497                  * Fatal error (EPERM, ENOSPC etc).
 498                  * It doesn't make sense to loop.
 499                  */
 500                 if (errno != EEXIST)
 501                         break;
 502         }
 503         /* We return the null string if we can't find a unique file name.  */
 504         pattern[0] = '\0';
 505         return -1;
 506 }
 507
 508 int git_mkstemp_mode(char *pattern, int mode)
 509 {
 510         /* mkstemp is just mkstemps with no suffix */
 511         return git_mkstemps_mode(pattern, 0, mode);
 512 }
 513
 514 int xmkstemp_mode(char *filename_template, int mode)
 515 {
 516         int fd;
 517         char origtemplate[PATH_MAX];
 518         strlcpy(origtemplate, filename_template, sizeof(origtemplate));
 519
 520         fd = git_mkstemp_mode(filename_template, mode);
 521         if (fd < 0) {
 522                 int saved_errno = errno;
 523                 const char *nonrelative_template;
 524
 525                 if (!filename_template[0])
 526                         filename_template = origtemplate;
 527
 528                 nonrelative_template = absolute_path(filename_template);
 529                 errno = saved_errno;
 530                 die_errno("Unable to create temporary file '%s'",
 531                         nonrelative_template);
 532         }
 533         return fd;
 534 }
 535
 536 /*
 537  * Some platforms return EINTR from fsync. Since fsync is invoked in some
 538  * cases by a wrapper that dies on failure, do not expose EINTR to callers.
 539  */
 540 static int fsync_loop(int fd)
 541 {
 542         int err;
 543
 544         do {
 545                 err = fsync(fd);
 546         } while (err < 0 && errno == EINTR);
 547         return err;
 548 }
 549
 550 int git_fsync(int fd, enum fsync_action action)
 551 {
 552         switch (action) {
 553         case FSYNC_WRITEOUT_ONLY:
 554                 count_fsync_writeout_only += 1;
 555
 556 #ifdef __APPLE__
 557                 /*
 558                  * On macOS, fsync just causes filesystem cache writeback but
 559                  * does not flush hardware caches.
 560                  */
 561                 return fsync_loop(fd);
 562 #endif
 563
 564 #ifdef HAVE_SYNC_FILE_RANGE
 565                 /*
 566                  * On linux 2.6.17 and above, sync_file_range is the way to
 567                  * issue a writeback without a hardware flush. An offset of
 568                  * 0 and size of 0 indicates writeout of the entire file and the
 569                  * wait flags ensure that all dirty data is written to the disk
 570                  * (potentially in a disk-side cache) before we continue.
 571                  */
 572
 573                 return sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WAIT_BEFORE |
 574                                                  SYNC_FILE_RANGE_WRITE |
 575                                                  SYNC_FILE_RANGE_WAIT_AFTER);
 576 #endif
 577
 578 #ifdef fsync_no_flush
 579                 return fsync_no_flush(fd);
 580 #endif
 581
 582                 errno = ENOSYS;
 583                 return -1;
 584
 585         case FSYNC_HARDWARE_FLUSH:
 586                 count_fsync_hardware_flush += 1;
 587
 588                 /*
 589                  * On macOS, a special fcntl is required to really flush the
 590                  * caches within the storage controller. As of this writing,
 591                  * this is a very expensive operation on Apple SSDs.
 592                  */
 593 #ifdef __APPLE__
 594                 return fcntl(fd, F_FULLFSYNC);
 595 #else
 596                 return fsync_loop(fd);
 597 #endif
 598         default:
 599                 BUG("unexpected git_fsync(%d) call", action);
 600         }
 601 }
 602
 603 static void log_trace_fsync_if(const char *key, intmax_t value)
 604 {
 605         if (value)
 606                 trace2_data_intmax("fsync", the_repository, key, value);
 607 }
 608
 609 void trace_git_fsync_stats(void)
 610 {
 611         log_trace_fsync_if("fsync/writeout-only", count_fsync_writeout_only);
 612         log_trace_fsync_if("fsync/hardware-flush", count_fsync_hardware_flush);
 613 }
 614
 615 static int warn_if_unremovable(const char *op, const char *file, int rc)
 616 {
 617         int err;
 618         if (!rc || errno == ENOENT)
 619                 return 0;
 620         err = errno;
 621         warning_errno("unable to %s '%s'", op, file);
 622         errno = err;
 623         return rc;
 624 }
 625
 626 int unlink_or_msg(const char *file, struct strbuf *err)
 627 {
 628         int rc = unlink(file);
 629
 630         assert(err);
 631
 632         if (!rc || errno == ENOENT)
 633                 return 0;
 634
 635         strbuf_addf(err, "unable to unlink '%s': %s",
 636                     file, strerror(errno));
 637         return -1;
 638 }
 639
 640 int unlink_or_warn(const char *file)
 641 {
 642         return warn_if_unremovable("unlink", file, unlink(file));
 643 }
 644
 645 int rmdir_or_warn(const char *file)
 646 {
 647         return warn_if_unremovable("rmdir", file, rmdir(file));
 648 }
 649
 650 int remove_or_warn(unsigned int mode, const char *file)
 651 {
 652         return S_ISGITLINK(mode) ? rmdir_or_warn(file) : unlink_or_warn(file);
 653 }
 654
 655 static int access_error_is_ok(int err, unsigned flag)
 656 {
 657         return (is_missing_file_error(err) ||
 658                 ((flag & ACCESS_EACCES_OK) && err == EACCES));
 659 }
 660
 661 int access_or_warn(const char *path, int mode, unsigned flag)
 662 {
 663         int ret = access(path, mode);
 664         if (ret && !access_error_is_ok(errno, flag))
 665                 warn_on_inaccessible(path);
 666         return ret;
 667 }
 668
 669 int access_or_die(const char *path, int mode, unsigned flag)
 670 {
 671         int ret = access(path, mode);
 672         if (ret && !access_error_is_ok(errno, flag))
 673                 die_errno(_("unable to access '%s'"), path);
 674         return ret;
 675 }
 676
 677 char *xgetcwd(void)
 678 {
 679         struct strbuf sb = STRBUF_INIT;
 680         if (strbuf_getcwd(&sb))
 681                 die_errno(_("unable to get current working directory"));
 682         return strbuf_detach(&sb, NULL);
 683 }
 684
 685 int xsnprintf(char *dst, size_t max, const char *fmt, ...)
 686 {
 687         va_list ap;
 688         int len;
 689
 690         va_start(ap, fmt);
 691         len = vsnprintf(dst, max, fmt, ap);
 692         va_end(ap);
 693
 694         if (len < 0)
 695                 BUG("your snprintf is broken");
 696         if (len >= max)
 697                 BUG("attempt to snprintf into too-small buffer");
 698         return len;
 699 }
 700
 701 void write_file_buf(const char *path, const char *buf, size_t len)
 702 {
 703         int fd = xopen(path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
 704         if (write_in_full(fd, buf, len) < 0)
 705                 die_errno(_("could not write to '%s'"), path);
 706         if (close(fd))
 707                 die_errno(_("could not close '%s'"), path);
 708 }
 709
 710 void write_file(const char *path, const char *fmt, ...)
 711 {
 712         va_list params;
 713         struct strbuf sb = STRBUF_INIT;
 714
 715         va_start(params, fmt);
 716         strbuf_vaddf(&sb, fmt, params);
 717         va_end(params);
 718
 719         strbuf_complete_line(&sb);
 720
 721         write_file_buf(path, sb.buf, sb.len);
 722         strbuf_release(&sb);
 723 }
 724
 725 void sleep_millisec(int millisec)
 726 {
 727         poll(NULL, 0, millisec);
 728 }
 729
 730 int xgethostname(char *buf, size_t len)
 731 {
 732         /*
 733          * If the full hostname doesn't fit in buf, POSIX does not
 734          * specify whether the buffer will be null-terminated, so to
 735          * be safe, do it ourselves.
 736          */
 737         int ret = gethostname(buf, len);
 738         if (!ret)
 739                 buf[len - 1] = 0;
 740         return ret;
 741 }
 742
 743 int is_empty_or_missing_file(const char *filename)
 744 {
 745         struct stat st;
 746
 747         if (stat(filename, &st) < 0) {
 748                 if (errno == ENOENT)
 749                         return 1;
 750                 die_errno(_("could not stat %s"), filename);
 751         }
 752
 753         return !st.st_size;
 754 }
 755
 756 int open_nofollow(const char *path, int flags)
 757 {
 758 #ifdef O_NOFOLLOW
 759         return open(path, flags | O_NOFOLLOW);
 760 #else
 761         struct stat st;
 762         if (lstat(path, &st) < 0)
 763                 return -1;
 764         if (S_ISLNK(st.st_mode)) {
 765                 errno = ELOOP;
 766                 return -1;
 767         }
 768         return open(path, flags);
 769 #endif
 770 }
 771
 772 int csprng_bytes(void *buf, size_t len)
 773 {
 774 #if defined(HAVE_ARC4RANDOM) || defined(HAVE_ARC4RANDOM_LIBBSD)
 775         /* This function never returns an error. */
 776         arc4random_buf(buf, len);
 777         return 0;
 778 #elif defined(HAVE_GETRANDOM)
 779         ssize_t res;
 780         char *p = buf;
 781         while (len) {
 782                 res = getrandom(p, len, 0);
 783                 if (res < 0)
 784                         return -1;
 785                 len -= res;
 786                 p += res;
 787         }
 788         return 0;
 789 #elif defined(HAVE_GETENTROPY)
 790         int res;
 791         char *p = buf;
 792         while (len) {
 793                 /* getentropy has a maximum size of 256 bytes. */
 794                 size_t chunk = len < 256 ? len : 256;
 795                 res = getentropy(p, chunk);
 796                 if (res < 0)
 797                         return -1;
 798                 len -= chunk;
 799                 p += chunk;
 800         }
 801         return 0;
 802 #elif defined(HAVE_RTLGENRANDOM)
 803         if (!RtlGenRandom(buf, len))
 804                 return -1;
 805         return 0;
 806 #elif defined(HAVE_OPENSSL_CSPRNG)
 807         int res = RAND_bytes(buf, len);
 808         if (res == 1)
 809                 return 0;
 810         if (res == -1)
 811                 errno = ENOTSUP;
 812         else
 813                 errno = EIO;
 814         return -1;
 815 #else
 816         ssize_t res;
 817         char *p = buf;
 818         int fd, err;
 819         fd = open("/dev/urandom", O_RDONLY);
 820         if (fd < 0)
 821                 return -1;
 822         while (len) {
 823                 res = xread(fd, p, len);
 824                 if (res < 0) {
 825                         err = errno;
 826                         close(fd);
 827                         errno = err;
 828                         return -1;
 829                 }
 830                 len -= res;
 831                 p += res;
 832         }
 833         close(fd);
 834         return 0;
 835 #endif
 836 }