wrapper.c

   1 /*
   2  * Various trivial helper wrappers around standard functions
   3  */
   4 #include "cache.h"
   5 #include "config.h"
   6
   7 static intmax_t count_fsync_writeout_only;
   8 static intmax_t count_fsync_hardware_flush;
   9
  10 #ifdef HAVE_RTLGENRANDOM
  11 /* This is required to get access to RtlGenRandom. */
  12 #define SystemFunction036 NTAPI SystemFunction036
  13 #include <NTSecAPI.h>
  14 #undef SystemFunction036
  15 #endif
  16
  17 static int memory_limit_check(size_t size, int gentle)
  18 {
  19         static size_t limit = 0;
  20         if (!limit) {
  21                 limit = git_env_ulong("GIT_ALLOC_LIMIT", 0);
  22                 if (!limit)
  23                         limit = SIZE_MAX;
  24         }
  25         if (size > limit) {
  26                 if (gentle) {
  27                         error("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
  28                               (uintmax_t)size, (uintmax_t)limit);
  29                         return -1;
  30                 } else
  31                         die("attempting to allocate %"PRIuMAX" over limit %"PRIuMAX,
  32                             (uintmax_t)size, (uintmax_t)limit);
  33         }
  34         return 0;
  35 }
  36
  37 char *xstrdup(const char *str)
  38 {
  39         char *ret = strdup(str);
  40         if (!ret)
  41                 die("Out of memory, strdup failed");
  42         return ret;
  43 }
  44
  45 static void *do_xmalloc(size_t size, int gentle)
  46 {
  47         void *ret;
  48
  49         if (memory_limit_check(size, gentle))
  50                 return NULL;
  51         ret = malloc(size);
  52         if (!ret && !size)
  53                 ret = malloc(1);
  54         if (!ret) {
  55                 if (!gentle)
  56                         die("Out of memory, malloc failed (tried to allocate %lu bytes)",
  57                             (unsigned long)size);
  58                 else {
  59                         error("Out of memory, malloc failed (tried to allocate %lu bytes)",
  60                               (unsigned long)size);
  61                         return NULL;
  62                 }
  63         }
  64 #ifdef XMALLOC_POISON
  65         memset(ret, 0xA5, size);
  66 #endif
  67         return ret;
  68 }
  69
  70 void *xmalloc(size_t size)
  71 {
  72         return do_xmalloc(size, 0);
  73 }
  74
  75 static void *do_xmallocz(size_t size, int gentle)
  76 {
  77         void *ret;
  78         if (unsigned_add_overflows(size, 1)) {
  79                 if (gentle) {
  80                         error("Data too large to fit into virtual memory space.");
  81                         return NULL;
  82                 } else
  83                         die("Data too large to fit into virtual memory space.");
  84         }
  85         ret = do_xmalloc(size + 1, gentle);
  86         if (ret)
  87                 ((char*)ret)[size] = 0;
  88         return ret;
  89 }
  90
  91 void *xmallocz(size_t size)
  92 {
  93         return do_xmallocz(size, 0);
  94 }
  95
  96 void *xmallocz_gently(size_t size)
  97 {
  98         return do_xmallocz(size, 1);
  99 }
 100
 101 /*
 102  * xmemdupz() allocates (len + 1) bytes of memory, duplicates "len" bytes of
 103  * "data" to the allocated memory, zero terminates the allocated memory,
 104  * and returns a pointer to the allocated memory. If the allocation fails,
 105  * the program dies.
 106  */
 107 void *xmemdupz(const void *data, size_t len)
 108 {
 109         return memcpy(xmallocz(len), data, len);
 110 }
 111
 112 char *xstrndup(const char *str, size_t len)
 113 {
 114         char *p = memchr(str, '\0', len);
 115         return xmemdupz(str, p ? p - str : len);
 116 }
 117
 118 int xstrncmpz(const char *s, const char *t, size_t len)
 119 {
 120         int res = strncmp(s, t, len);
 121         if (res)
 122                 return res;
 123         return s[len] == '\0' ? 0 : 1;
 124 }
 125
 126 void *xrealloc(void *ptr, size_t size)
 127 {
 128         void *ret;
 129
 130         if (!size) {
 131                 free(ptr);
 132                 return xmalloc(0);
 133         }
 134
 135         memory_limit_check(size, 0);
 136         ret = realloc(ptr, size);
 137         if (!ret)
 138                 die("Out of memory, realloc failed");
 139         return ret;
 140 }
 141
 142 void *xcalloc(size_t nmemb, size_t size)
 143 {
 144         void *ret;
 145
 146         if (unsigned_mult_overflows(nmemb, size))
 147                 die("data too large to fit into virtual memory space");
 148
 149         memory_limit_check(size * nmemb, 0);
 150         ret = calloc(nmemb, size);
 151         if (!ret && (!nmemb || !size))
 152                 ret = calloc(1, 1);
 153         if (!ret)
 154                 die("Out of memory, calloc failed");
 155         return ret;
 156 }
 157
 158 void xsetenv(const char *name, const char *value, int overwrite)
 159 {
 160         if (setenv(name, value, overwrite))
 161                 die_errno(_("could not setenv '%s'"), name ? name : "(null)");
 162 }
 163
 164 /*
 165  * Limit size of IO chunks, because huge chunks only cause pain.  OS X
 166  * 64-bit is buggy, returning EINVAL if len >= INT_MAX; and even in
 167  * the absence of bugs, large chunks can result in bad latencies when
 168  * you decide to kill the process.
 169  *
 170  * We pick 8 MiB as our default, but if the platform defines SSIZE_MAX
 171  * that is smaller than that, clip it to SSIZE_MAX, as a call to
 172  * read(2) or write(2) larger than that is allowed to fail.  As the last
 173  * resort, we allow a port to pass via CFLAGS e.g. "-DMAX_IO_SIZE=value"
 174  * to override this, if the definition of SSIZE_MAX given by the platform
 175  * is broken.
 176  */
 177 #ifndef MAX_IO_SIZE
 178 # define MAX_IO_SIZE_DEFAULT (8*1024*1024)
 179 # if defined(SSIZE_MAX) && (SSIZE_MAX < MAX_IO_SIZE_DEFAULT)
 180 #  define MAX_IO_SIZE SSIZE_MAX
 181 # else
 182 #  define MAX_IO_SIZE MAX_IO_SIZE_DEFAULT
 183 # endif
 184 #endif
 185
 186 /**
 187  * xopen() is the same as open(), but it die()s if the open() fails.
 188  */
 189 int xopen(const char *path, int oflag, ...)
 190 {
 191         mode_t mode = 0;
 192         va_list ap;
 193
 194         /*
 195          * va_arg() will have undefined behavior if the specified type is not
 196          * compatible with the argument type. Since integers are promoted to
 197          * ints, we fetch the next argument as an int, and then cast it to a
 198          * mode_t to avoid undefined behavior.
 199          */
 200         va_start(ap, oflag);
 201         if (oflag & O_CREAT)
 202                 mode = va_arg(ap, int);
 203         va_end(ap);
 204
 205         for (;;) {
 206                 int fd = open(path, oflag, mode);
 207                 if (fd >= 0)
 208                         return fd;
 209                 if (errno == EINTR)
 210                         continue;
 211
 212                 if ((oflag & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL))
 213                         die_errno(_("unable to create '%s'"), path);
 214                 else if ((oflag & O_RDWR) == O_RDWR)
 215                         die_errno(_("could not open '%s' for reading and writing"), path);
 216                 else if ((oflag & O_WRONLY) == O_WRONLY)
 217                         die_errno(_("could not open '%s' for writing"), path);
 218                 else
 219                         die_errno(_("could not open '%s' for reading"), path);
 220         }
 221 }
 222
 223 static int handle_nonblock(int fd, short poll_events, int err)
 224 {
 225         struct pollfd pfd;
 226
 227         if (err != EAGAIN && err != EWOULDBLOCK)
 228                 return 0;
 229
 230         pfd.fd = fd;
 231         pfd.events = poll_events;
 232
 233         /*
 234          * no need to check for errors, here;
 235          * a subsequent read/write will detect unrecoverable errors
 236          */
 237         poll(&pfd, 1, -1);
 238         return 1;
 239 }
 240
 241 /*
 242  * xread() is the same a read(), but it automatically restarts read()
 243  * operations with a recoverable error (EAGAIN and EINTR). xread()
 244  * DOES NOT GUARANTEE that "len" bytes is read even if the data is available.
 245  */
 246 ssize_t xread(int fd, void *buf, size_t len)
 247 {
 248         ssize_t nr;
 249         if (len > MAX_IO_SIZE)
 250                 len = MAX_IO_SIZE;
 251         while (1) {
 252                 nr = read(fd, buf, len);
 253                 if (nr < 0) {
 254                         if (errno == EINTR)
 255                                 continue;
 256                         if (handle_nonblock(fd, POLLIN, errno))
 257                                 continue;
 258                 }
 259                 return nr;
 260         }
 261 }
 262
 263 /*
 264  * xwrite() is the same a write(), but it automatically restarts write()
 265  * operations with a recoverable error (EAGAIN and EINTR). xwrite() DOES NOT
 266  * GUARANTEE that "len" bytes is written even if the operation is successful.
 267  */
 268 ssize_t xwrite(int fd, const void *buf, size_t len)
 269 {
 270         ssize_t nr;
 271         if (len > MAX_IO_SIZE)
 272                 len = MAX_IO_SIZE;
 273         while (1) {
 274                 nr = write(fd, buf, len);
 275                 if (nr < 0) {
 276                         if (errno == EINTR)
 277                                 continue;
 278                         if (handle_nonblock(fd, POLLOUT, errno))
 279                                 continue;
 280                 }
 281
 282                 return nr;
 283         }
 284 }
 285
 286 /*
 287  * xpread() is the same as pread(), but it automatically restarts pread()
 288  * operations with a recoverable error (EAGAIN and EINTR). xpread() DOES
 289  * NOT GUARANTEE that "len" bytes is read even if the data is available.
 290  */
 291 ssize_t xpread(int fd, void *buf, size_t len, off_t offset)
 292 {
 293         ssize_t nr;
 294         if (len > MAX_IO_SIZE)
 295                 len = MAX_IO_SIZE;
 296         while (1) {
 297                 nr = pread(fd, buf, len, offset);
 298                 if ((nr < 0) && (errno == EAGAIN || errno == EINTR))
 299                         continue;
 300                 return nr;
 301         }
 302 }
 303
 304 ssize_t read_in_full(int fd, void *buf, size_t count)
 305 {
 306         char *p = buf;
 307         ssize_t total = 0;
 308
 309         while (count > 0) {
 310                 ssize_t loaded = xread(fd, p, count);
 311                 if (loaded < 0)
 312                         return -1;
 313                 if (loaded == 0)
 314                         return total;
 315                 count -= loaded;
 316                 p += loaded;
 317                 total += loaded;
 318         }
 319
 320         return total;
 321 }
 322
 323 ssize_t write_in_full(int fd, const void *buf, size_t count)
 324 {
 325         const char *p = buf;
 326         ssize_t total = 0;
 327
 328         while (count > 0) {
 329                 ssize_t written = xwrite(fd, p, count);
 330                 if (written < 0)
 331                         return -1;
 332                 if (!written) {
 333                         errno = ENOSPC;
 334                         return -1;
 335                 }
 336                 count -= written;
 337                 p += written;
 338                 total += written;
 339         }
 340
 341         return total;
 342 }
 343
 344 ssize_t pread_in_full(int fd, void *buf, size_t count, off_t offset)
 345 {
 346         char *p = buf;
 347         ssize_t total = 0;
 348
 349         while (count > 0) {
 350                 ssize_t loaded = xpread(fd, p, count, offset);
 351                 if (loaded < 0)
 352                         return -1;
 353                 if (loaded == 0)
 354                         return total;
 355                 count -= loaded;
 356                 p += loaded;
 357                 total += loaded;
 358                 offset += loaded;
 359         }
 360
 361         return total;
 362 }
 363
 364 int xdup(int fd)
 365 {
 366         int ret = dup(fd);
 367         if (ret < 0)
 368                 die_errno("dup failed");
 369         return ret;
 370 }
 371
 372 /**
 373  * xfopen() is the same as fopen(), but it die()s if the fopen() fails.
 374  */
 375 FILE *xfopen(const char *path, const char *mode)
 376 {
 377         for (;;) {
 378                 FILE *fp = fopen(path, mode);
 379                 if (fp)
 380                         return fp;
 381                 if (errno == EINTR)
 382                         continue;
 383
 384                 if (*mode && mode[1] == '+')
 385                         die_errno(_("could not open '%s' for reading and writing"), path);
 386                 else if (*mode == 'w' || *mode == 'a')
 387                         die_errno(_("could not open '%s' for writing"), path);
 388                 else
 389                         die_errno(_("could not open '%s' for reading"), path);
 390         }
 391 }
 392
 393 FILE *xfdopen(int fd, const char *mode)
 394 {
 395         FILE *stream = fdopen(fd, mode);
 396         if (!stream)
 397                 die_errno("Out of memory? fdopen failed");
 398         return stream;
 399 }
 400
 401 FILE *fopen_for_writing(const char *path)
 402 {
 403         FILE *ret = fopen(path, "w");
 404
 405         if (!ret && errno == EPERM) {
 406                 if (!unlink(path))
 407                         ret = fopen(path, "w");
 408                 else
 409                         errno = EPERM;
 410         }
 411         return ret;
 412 }
 413
 414 static void warn_on_inaccessible(const char *path)
 415 {
 416         warning_errno(_("unable to access '%s'"), path);
 417 }
 418
 419 int warn_on_fopen_errors(const char *path)
 420 {
 421         if (errno != ENOENT && errno != ENOTDIR) {
 422                 warn_on_inaccessible(path);
 423                 return -1;
 424         }
 425
 426         return 0;
 427 }
 428
 429 FILE *fopen_or_warn(const char *path, const char *mode)
 430 {
 431         FILE *fp = fopen(path, mode);
 432
 433         if (fp)
 434                 return fp;
 435
 436         warn_on_fopen_errors(path);
 437         return NULL;
 438 }
 439
 440 int xmkstemp(char *filename_template)
 441 {
 442         int fd;
 443         char origtemplate[PATH_MAX];
 444         strlcpy(origtemplate, filename_template, sizeof(origtemplate));
 445
 446         fd = mkstemp(filename_template);
 447         if (fd < 0) {
 448                 int saved_errno = errno;
 449                 const char *nonrelative_template;
 450
 451                 if (strlen(filename_template) != strlen(origtemplate))
 452                         filename_template = origtemplate;
 453
 454                 nonrelative_template = absolute_path(filename_template);
 455                 errno = saved_errno;
 456                 die_errno("Unable to create temporary file '%s'",
 457                         nonrelative_template);
 458         }
 459         return fd;
 460 }
 461
 462 /* Adapted from libiberty's mkstemp.c. */
 463
 464 #undef TMP_MAX
 465 #define TMP_MAX 16384
 466
 467 int git_mkstemps_mode(char *pattern, int suffix_len, int mode)
 468 {
 469         static const char letters[] =
 470                 "abcdefghijklmnopqrstuvwxyz"
 471                 "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 472                 "0123456789";
 473         static const int num_letters = ARRAY_SIZE(letters) - 1;
 474         static const char x_pattern[] = "XXXXXX";
 475         static const int num_x = ARRAY_SIZE(x_pattern) - 1;
 476         char *filename_template;
 477         size_t len;
 478         int fd, count;
 479
 480         len = strlen(pattern);
 481
 482         if (len < num_x + suffix_len) {
 483                 errno = EINVAL;
 484                 return -1;
 485         }
 486
 487         if (strncmp(&pattern[len - num_x - suffix_len], x_pattern, num_x)) {
 488                 errno = EINVAL;
 489                 return -1;
 490         }
 491
 492         /*
 493          * Replace pattern's XXXXXX characters with randomness.
 494          * Try TMP_MAX different filenames.
 495          */
 496         filename_template = &pattern[len - num_x - suffix_len];
 497         for (count = 0; count < TMP_MAX; ++count) {
 498                 int i;
 499                 uint64_t v;
 500                 if (csprng_bytes(&v, sizeof(v)) < 0)
 501                         return error_errno("unable to get random bytes for temporary file");
 502
 503                 /* Fill in the random bits. */
 504                 for (i = 0; i < num_x; i++) {
 505                         filename_template[i] = letters[v % num_letters];
 506                         v /= num_letters;
 507                 }
 508
 509                 fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
 510                 if (fd >= 0)
 511                         return fd;
 512                 /*
 513                  * Fatal error (EPERM, ENOSPC etc).
 514                  * It doesn't make sense to loop.
 515                  */
 516                 if (errno != EEXIST)
 517                         break;
 518         }
 519         /* We return the null string if we can't find a unique file name.  */
 520         pattern[0] = '\0';
 521         return -1;
 522 }
 523
 524 int git_mkstemp_mode(char *pattern, int mode)
 525 {
 526         /* mkstemp is just mkstemps with no suffix */
 527         return git_mkstemps_mode(pattern, 0, mode);
 528 }
 529
 530 int xmkstemp_mode(char *filename_template, int mode)
 531 {
 532         int fd;
 533         char origtemplate[PATH_MAX];
 534         strlcpy(origtemplate, filename_template, sizeof(origtemplate));
 535
 536         fd = git_mkstemp_mode(filename_template, mode);
 537         if (fd < 0) {
 538                 int saved_errno = errno;
 539                 const char *nonrelative_template;
 540
 541                 if (!filename_template[0])
 542                         filename_template = origtemplate;
 543
 544                 nonrelative_template = absolute_path(filename_template);
 545                 errno = saved_errno;
 546                 die_errno("Unable to create temporary file '%s'",
 547                         nonrelative_template);
 548         }
 549         return fd;
 550 }
 551
 552 /*
 553  * Some platforms return EINTR from fsync. Since fsync is invoked in some
 554  * cases by a wrapper that dies on failure, do not expose EINTR to callers.
 555  */
 556 static int fsync_loop(int fd)
 557 {
 558         int err;
 559
 560         do {
 561                 err = fsync(fd);
 562         } while (err < 0 && errno == EINTR);
 563         return err;
 564 }
 565
 566 int git_fsync(int fd, enum fsync_action action)
 567 {
 568         switch (action) {
 569         case FSYNC_WRITEOUT_ONLY:
 570                 count_fsync_writeout_only += 1;
 571
 572 #ifdef __APPLE__
 573                 /*
 574                  * On macOS, fsync just causes filesystem cache writeback but
 575                  * does not flush hardware caches.
 576                  */
 577                 return fsync_loop(fd);
 578 #endif
 579
 580 #ifdef HAVE_SYNC_FILE_RANGE
 581                 /*
 582                  * On linux 2.6.17 and above, sync_file_range is the way to
 583                  * issue a writeback without a hardware flush. An offset of
 584                  * 0 and size of 0 indicates writeout of the entire file and the
 585                  * wait flags ensure that all dirty data is written to the disk
 586                  * (potentially in a disk-side cache) before we continue.
 587                  */
 588
 589                 return sync_file_range(fd, 0, 0, SYNC_FILE_RANGE_WAIT_BEFORE |
 590                                                  SYNC_FILE_RANGE_WRITE |
 591                                                  SYNC_FILE_RANGE_WAIT_AFTER);
 592 #endif
 593
 594 #ifdef fsync_no_flush
 595                 return fsync_no_flush(fd);
 596 #endif
 597
 598                 errno = ENOSYS;
 599                 return -1;
 600
 601         case FSYNC_HARDWARE_FLUSH:
 602                 count_fsync_hardware_flush += 1;
 603
 604                 /*
 605                  * On macOS, a special fcntl is required to really flush the
 606                  * caches within the storage controller. As of this writing,
 607                  * this is a very expensive operation on Apple SSDs.
 608                  */
 609 #ifdef __APPLE__
 610                 return fcntl(fd, F_FULLFSYNC);
 611 #else
 612                 return fsync_loop(fd);
 613 #endif
 614         default:
 615                 BUG("unexpected git_fsync(%d) call", action);
 616         }
 617 }
 618
 619 static void log_trace_fsync_if(const char *key, intmax_t value)
 620 {
 621         if (value)
 622                 trace2_data_intmax("fsync", the_repository, key, value);
 623 }
 624
 625 void trace_git_fsync_stats(void)
 626 {
 627         log_trace_fsync_if("fsync/writeout-only", count_fsync_writeout_only);
 628         log_trace_fsync_if("fsync/hardware-flush", count_fsync_hardware_flush);
 629 }
 630
 631 static int warn_if_unremovable(const char *op, const char *file, int rc)
 632 {
 633         int err;
 634         if (!rc || errno == ENOENT)
 635                 return 0;
 636         err = errno;
 637         warning_errno("unable to %s '%s'", op, file);
 638         errno = err;
 639         return rc;
 640 }
 641
 642 int unlink_or_msg(const char *file, struct strbuf *err)
 643 {
 644         int rc = unlink(file);
 645
 646         assert(err);
 647
 648         if (!rc || errno == ENOENT)
 649                 return 0;
 650
 651         strbuf_addf(err, "unable to unlink '%s': %s",
 652                     file, strerror(errno));
 653         return -1;
 654 }
 655
 656 int unlink_or_warn(const char *file)
 657 {
 658         return warn_if_unremovable("unlink", file, unlink(file));
 659 }
 660
 661 int rmdir_or_warn(const char *file)
 662 {
 663         return warn_if_unremovable("rmdir", file, rmdir(file));
 664 }
 665
 666 int remove_or_warn(unsigned int mode, const char *file)
 667 {
 668         return S_ISGITLINK(mode) ? rmdir_or_warn(file) : unlink_or_warn(file);
 669 }
 670
 671 static int access_error_is_ok(int err, unsigned flag)
 672 {
 673         return (is_missing_file_error(err) ||
 674                 ((flag & ACCESS_EACCES_OK) && err == EACCES));
 675 }
 676
 677 int access_or_warn(const char *path, int mode, unsigned flag)
 678 {
 679         int ret = access(path, mode);
 680         if (ret && !access_error_is_ok(errno, flag))
 681                 warn_on_inaccessible(path);
 682         return ret;
 683 }
 684
 685 int access_or_die(const char *path, int mode, unsigned flag)
 686 {
 687         int ret = access(path, mode);
 688         if (ret && !access_error_is_ok(errno, flag))
 689                 die_errno(_("unable to access '%s'"), path);
 690         return ret;
 691 }
 692
 693 char *xgetcwd(void)
 694 {
 695         struct strbuf sb = STRBUF_INIT;
 696         if (strbuf_getcwd(&sb))
 697                 die_errno(_("unable to get current working directory"));
 698         return strbuf_detach(&sb, NULL);
 699 }
 700
 701 int xsnprintf(char *dst, size_t max, const char *fmt, ...)
 702 {
 703         va_list ap;
 704         int len;
 705
 706         va_start(ap, fmt);
 707         len = vsnprintf(dst, max, fmt, ap);
 708         va_end(ap);
 709
 710         if (len < 0)
 711                 BUG("your snprintf is broken");
 712         if (len >= max)
 713                 BUG("attempt to snprintf into too-small buffer");
 714         return len;
 715 }
 716
 717 void write_file_buf(const char *path, const char *buf, size_t len)
 718 {
 719         int fd = xopen(path, O_WRONLY | O_CREAT | O_TRUNC, 0666);
 720         if (write_in_full(fd, buf, len) < 0)
 721                 die_errno(_("could not write to '%s'"), path);
 722         if (close(fd))
 723                 die_errno(_("could not close '%s'"), path);
 724 }
 725
 726 void write_file(const char *path, const char *fmt, ...)
 727 {
 728         va_list params;
 729         struct strbuf sb = STRBUF_INIT;
 730
 731         va_start(params, fmt);
 732         strbuf_vaddf(&sb, fmt, params);
 733         va_end(params);
 734
 735         strbuf_complete_line(&sb);
 736
 737         write_file_buf(path, sb.buf, sb.len);
 738         strbuf_release(&sb);
 739 }
 740
 741 void sleep_millisec(int millisec)
 742 {
 743         poll(NULL, 0, millisec);
 744 }
 745
 746 int xgethostname(char *buf, size_t len)
 747 {
 748         /*
 749          * If the full hostname doesn't fit in buf, POSIX does not
 750          * specify whether the buffer will be null-terminated, so to
 751          * be safe, do it ourselves.
 752          */
 753         int ret = gethostname(buf, len);
 754         if (!ret)
 755                 buf[len - 1] = 0;
 756         return ret;
 757 }
 758
 759 int is_empty_or_missing_file(const char *filename)
 760 {
 761         struct stat st;
 762
 763         if (stat(filename, &st) < 0) {
 764                 if (errno == ENOENT)
 765                         return 1;
 766                 die_errno(_("could not stat %s"), filename);
 767         }
 768
 769         return !st.st_size;
 770 }
 771
 772 int open_nofollow(const char *path, int flags)
 773 {
 774 #ifdef O_NOFOLLOW
 775         return open(path, flags | O_NOFOLLOW);
 776 #else
 777         struct stat st;
 778         if (lstat(path, &st) < 0)
 779                 return -1;
 780         if (S_ISLNK(st.st_mode)) {
 781                 errno = ELOOP;
 782                 return -1;
 783         }
 784         return open(path, flags);
 785 #endif
 786 }
 787
 788 int csprng_bytes(void *buf, size_t len)
 789 {
 790 #if defined(HAVE_ARC4RANDOM) || defined(HAVE_ARC4RANDOM_LIBBSD)
 791         /* This function never returns an error. */
 792         arc4random_buf(buf, len);
 793         return 0;
 794 #elif defined(HAVE_GETRANDOM)
 795         ssize_t res;
 796         char *p = buf;
 797         while (len) {
 798                 res = getrandom(p, len, 0);
 799                 if (res < 0)
 800                         return -1;
 801                 len -= res;
 802                 p += res;
 803         }
 804         return 0;
 805 #elif defined(HAVE_GETENTROPY)
 806         int res;
 807         char *p = buf;
 808         while (len) {
 809                 /* getentropy has a maximum size of 256 bytes. */
 810                 size_t chunk = len < 256 ? len : 256;
 811                 res = getentropy(p, chunk);
 812                 if (res < 0)
 813                         return -1;
 814                 len -= chunk;
 815                 p += chunk;
 816         }
 817         return 0;
 818 #elif defined(HAVE_RTLGENRANDOM)
 819         if (!RtlGenRandom(buf, len))
 820                 return -1;
 821         return 0;
 822 #elif defined(HAVE_OPENSSL_CSPRNG)
 823         int res = RAND_bytes(buf, len);
 824         if (res == 1)
 825                 return 0;
 826         if (res == -1)
 827                 errno = ENOTSUP;
 828         else
 829                 errno = EIO;
 830         return -1;
 831 #else
 832         ssize_t res;
 833         char *p = buf;
 834         int fd, err;
 835         fd = open("/dev/urandom", O_RDONLY);
 836         if (fd < 0)
 837                 return -1;
 838         while (len) {
 839                 res = xread(fd, p, len);
 840                 if (res < 0) {
 841                         err = errno;
 842                         close(fd);
 843                         errno = err;
 844                         return -1;
 845                 }
 846                 len -= res;
 847                 p += res;
 848         }
 849         close(fd);
 850         return 0;
 851 #endif
 852 }