wrapper.c

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