wrapper.c

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