src/basic/fileio.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #include <ctype.h>
   4 #include <errno.h>
   5 #include <fcntl.h>
   6 #include <limits.h>
   7 #include <stdarg.h>
   8 #include <stdint.h>
   9 #include <stdio_ext.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <sys/stat.h>
  13 #include <sys/types.h>
  14 #include <unistd.h>
  15
  16 #include "alloc-util.h"
  17 #include "fd-util.h"
  18 #include "fileio.h"
  19 #include "fs-util.h"
  20 #include "log.h"
  21 #include "macro.h"
  22 #include "missing.h"
  23 #include "parse-util.h"
  24 #include "path-util.h"
  25 #include "stdio-util.h"
  26 #include "string-util.h"
  27 #include "tmpfile-util.h"
  28
  29 #define READ_FULL_BYTES_MAX (4U*1024U*1024U)
  30
  31 int write_string_stream_ts(
  32                 FILE *f,
  33                 const char *line,
  34                 WriteStringFileFlags flags,
  35                 struct timespec *ts) {
  36
  37         bool needs_nl;
  38         int r;
  39
  40         assert(f);
  41         assert(line);
  42
  43         if (ferror(f))
  44                 return -EIO;
  45
  46         needs_nl = !(flags & WRITE_STRING_FILE_AVOID_NEWLINE) && !endswith(line, "\n");
  47
  48         if (needs_nl && (flags & WRITE_STRING_FILE_DISABLE_BUFFER)) {
  49                 /* If STDIO buffering was disabled, then let's append the newline character to the string itself, so
  50                  * that the write goes out in one go, instead of two */
  51
  52                 line = strjoina(line, "\n");
  53                 needs_nl = false;
  54         }
  55
  56         if (fputs(line, f) == EOF)
  57                 return -errno;
  58
  59         if (needs_nl)
  60                 if (fputc('\n', f) == EOF)
  61                         return -errno;
  62
  63         if (flags & WRITE_STRING_FILE_SYNC)
  64                 r = fflush_sync_and_check(f);
  65         else
  66                 r = fflush_and_check(f);
  67         if (r < 0)
  68                 return r;
  69
  70         if (ts) {
  71                 struct timespec twice[2] = {*ts, *ts};
  72
  73                 if (futimens(fileno(f), twice) < 0)
  74                         return -errno;
  75         }
  76
  77         return 0;
  78 }
  79
  80 static int write_string_file_atomic(
  81                 const char *fn,
  82                 const char *line,
  83                 WriteStringFileFlags flags,
  84                 struct timespec *ts) {
  85
  86         _cleanup_fclose_ FILE *f = NULL;
  87         _cleanup_free_ char *p = NULL;
  88         int r;
  89
  90         assert(fn);
  91         assert(line);
  92
  93         r = fopen_temporary(fn, &f, &p);
  94         if (r < 0)
  95                 return r;
  96
  97         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  98         (void) fchmod_umask(fileno(f), 0644);
  99
 100         r = write_string_stream_ts(f, line, flags, ts);
 101         if (r < 0)
 102                 goto fail;
 103
 104         if (rename(p, fn) < 0) {
 105                 r = -errno;
 106                 goto fail;
 107         }
 108
 109         return 0;
 110
 111 fail:
 112         (void) unlink(p);
 113         return r;
 114 }
 115
 116 int write_string_file_ts(
 117                 const char *fn,
 118                 const char *line,
 119                 WriteStringFileFlags flags,
 120                 struct timespec *ts) {
 121
 122         _cleanup_fclose_ FILE *f = NULL;
 123         int q, r;
 124
 125         assert(fn);
 126         assert(line);
 127
 128         /* We don't know how to verify whether the file contents was already on-disk. */
 129         assert(!((flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE) && (flags & WRITE_STRING_FILE_SYNC)));
 130
 131         if (flags & WRITE_STRING_FILE_ATOMIC) {
 132                 assert(flags & WRITE_STRING_FILE_CREATE);
 133
 134                 r = write_string_file_atomic(fn, line, flags, ts);
 135                 if (r < 0)
 136                         goto fail;
 137
 138                 return r;
 139         } else
 140                 assert(!ts);
 141
 142         if (flags & WRITE_STRING_FILE_CREATE) {
 143                 f = fopen(fn, "we");
 144                 if (!f) {
 145                         r = -errno;
 146                         goto fail;
 147                 }
 148         } else {
 149                 int fd;
 150
 151                 /* We manually build our own version of fopen(..., "we") that
 152                  * works without O_CREAT */
 153                 fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY | ((flags & WRITE_STRING_FILE_NOFOLLOW) ? O_NOFOLLOW : 0));
 154                 if (fd < 0) {
 155                         r = -errno;
 156                         goto fail;
 157                 }
 158
 159                 f = fdopen(fd, "w");
 160                 if (!f) {
 161                         r = -errno;
 162                         safe_close(fd);
 163                         goto fail;
 164                 }
 165         }
 166
 167         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 168
 169         if (flags & WRITE_STRING_FILE_DISABLE_BUFFER)
 170                 setvbuf(f, NULL, _IONBF, 0);
 171
 172         r = write_string_stream_ts(f, line, flags, ts);
 173         if (r < 0)
 174                 goto fail;
 175
 176         return 0;
 177
 178 fail:
 179         if (!(flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE))
 180                 return r;
 181
 182         f = safe_fclose(f);
 183
 184         /* OK, the operation failed, but let's see if the right
 185          * contents in place already. If so, eat up the error. */
 186
 187         q = verify_file(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
 188         if (q <= 0)
 189                 return r;
 190
 191         return 0;
 192 }
 193
 194 int write_string_filef(
 195                 const char *fn,
 196                 WriteStringFileFlags flags,
 197                 const char *format, ...) {
 198
 199         _cleanup_free_ char *p = NULL;
 200         va_list ap;
 201         int r;
 202
 203         va_start(ap, format);
 204         r = vasprintf(&p, format, ap);
 205         va_end(ap);
 206
 207         if (r < 0)
 208                 return -ENOMEM;
 209
 210         return write_string_file(fn, p, flags);
 211 }
 212
 213 int read_one_line_file(const char *fn, char **line) {
 214         _cleanup_fclose_ FILE *f = NULL;
 215
 216         assert(fn);
 217         assert(line);
 218
 219         f = fopen(fn, "re");
 220         if (!f)
 221                 return -errno;
 222
 223         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 224
 225         return read_line(f, LONG_LINE_MAX, line);
 226 }
 227
 228 int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
 229         _cleanup_fclose_ FILE *f = NULL;
 230         _cleanup_free_ char *buf = NULL;
 231         size_t l, k;
 232
 233         assert(fn);
 234         assert(blob);
 235
 236         l = strlen(blob);
 237
 238         if (accept_extra_nl && endswith(blob, "\n"))
 239                 accept_extra_nl = false;
 240
 241         buf = malloc(l + accept_extra_nl + 1);
 242         if (!buf)
 243                 return -ENOMEM;
 244
 245         f = fopen(fn, "re");
 246         if (!f)
 247                 return -errno;
 248
 249         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 250
 251         /* We try to read one byte more than we need, so that we know whether we hit eof */
 252         errno = 0;
 253         k = fread(buf, 1, l + accept_extra_nl + 1, f);
 254         if (ferror(f))
 255                 return errno > 0 ? -errno : -EIO;
 256
 257         if (k != l && k != l + accept_extra_nl)
 258                 return 0;
 259         if (memcmp(buf, blob, l) != 0)
 260                 return 0;
 261         if (k > l && buf[l] != '\n')
 262                 return 0;
 263
 264         return 1;
 265 }
 266
 267 int read_full_stream(
 268                 FILE *f,
 269                 char **ret_contents,
 270                 size_t *ret_size) {
 271
 272         _cleanup_free_ char *buf = NULL;
 273         struct stat st;
 274         size_t n, l;
 275         int fd;
 276
 277         assert(f);
 278         assert(ret_contents);
 279
 280         n = LINE_MAX; /* Start size */
 281
 282         fd = fileno(f);
 283         if (fd >= 0) { /* If the FILE* object is backed by an fd (as opposed to memory or such, see fmemopen(), let's
 284                         * optimize our buffering) */
 285
 286                 if (fstat(fileno(f), &st) < 0)
 287                         return -errno;
 288
 289                 if (S_ISREG(st.st_mode)) {
 290
 291                         /* Safety check */
 292                         if (st.st_size > READ_FULL_BYTES_MAX)
 293                                 return -E2BIG;
 294
 295                         /* Start with the right file size, but be prepared for files from /proc which generally report a file
 296                          * size of 0. Note that we increase the size to read here by one, so that the first read attempt
 297                          * already makes us notice the EOF. */
 298                         if (st.st_size > 0)
 299                                 n = st.st_size + 1;
 300                 }
 301         }
 302
 303         l = 0;
 304         for (;;) {
 305                 char *t;
 306                 size_t k;
 307
 308                 t = realloc(buf, n + 1);
 309                 if (!t)
 310                         return -ENOMEM;
 311
 312                 buf = t;
 313                 errno = 0;
 314                 k = fread(buf + l, 1, n - l, f);
 315                 if (k > 0)
 316                         l += k;
 317
 318                 if (ferror(f))
 319                         return errno > 0 ? -errno : -EIO;
 320
 321                 if (feof(f))
 322                         break;
 323
 324                 /* We aren't expecting fread() to return a short read outside
 325                  * of (error && eof), assert buffer is full and enlarge buffer.
 326                  */
 327                 assert(l == n);
 328
 329                 /* Safety check */
 330                 if (n >= READ_FULL_BYTES_MAX)
 331                         return -E2BIG;
 332
 333                 n = MIN(n * 2, READ_FULL_BYTES_MAX);
 334         }
 335
 336         if (!ret_size) {
 337                 /* Safety check: if the caller doesn't want to know the size of what we just read it will rely on the
 338                  * trailing NUL byte. But if there's an embedded NUL byte, then we should refuse operation as otherwise
 339                  * there'd be ambiguity about what we just read. */
 340
 341                 if (memchr(buf, 0, l))
 342                         return -EBADMSG;
 343         }
 344
 345         buf[l] = 0;
 346         *ret_contents = TAKE_PTR(buf);
 347
 348         if (ret_size)
 349                 *ret_size = l;
 350
 351         return 0;
 352 }
 353
 354 int read_full_file(const char *fn, char **contents, size_t *size) {
 355         _cleanup_fclose_ FILE *f = NULL;
 356
 357         assert(fn);
 358         assert(contents);
 359
 360         f = fopen(fn, "re");
 361         if (!f)
 362                 return -errno;
 363
 364         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 365
 366         return read_full_stream(f, contents, size);
 367 }
 368
 369 int executable_is_script(const char *path, char **interpreter) {
 370         _cleanup_free_ char *line = NULL;
 371         size_t len;
 372         char *ans;
 373         int r;
 374
 375         assert(path);
 376
 377         r = read_one_line_file(path, &line);
 378         if (r == -ENOBUFS) /* First line overly long? if so, then it's not a script */
 379                 return 0;
 380         if (r < 0)
 381                 return r;
 382
 383         if (!startswith(line, "#!"))
 384                 return 0;
 385
 386         ans = strstrip(line + 2);
 387         len = strcspn(ans, " \t");
 388
 389         if (len == 0)
 390                 return 0;
 391
 392         ans = strndup(ans, len);
 393         if (!ans)
 394                 return -ENOMEM;
 395
 396         *interpreter = ans;
 397         return 1;
 398 }
 399
 400 /**
 401  * Retrieve one field from a file like /proc/self/status.  pattern
 402  * should not include whitespace or the delimiter (':'). pattern matches only
 403  * the beginning of a line. Whitespace before ':' is skipped. Whitespace and
 404  * zeros after the ':' will be skipped. field must be freed afterwards.
 405  * terminator specifies the terminating characters of the field value (not
 406  * included in the value).
 407  */
 408 int get_proc_field(const char *filename, const char *pattern, const char *terminator, char **field) {
 409         _cleanup_free_ char *status = NULL;
 410         char *t, *f;
 411         size_t len;
 412         int r;
 413
 414         assert(terminator);
 415         assert(filename);
 416         assert(pattern);
 417         assert(field);
 418
 419         r = read_full_file(filename, &status, NULL);
 420         if (r < 0)
 421                 return r;
 422
 423         t = status;
 424
 425         do {
 426                 bool pattern_ok;
 427
 428                 do {
 429                         t = strstr(t, pattern);
 430                         if (!t)
 431                                 return -ENOENT;
 432
 433                         /* Check that pattern occurs in beginning of line. */
 434                         pattern_ok = (t == status || t[-1] == '\n');
 435
 436                         t += strlen(pattern);
 437
 438                 } while (!pattern_ok);
 439
 440                 t += strspn(t, " \t");
 441                 if (!*t)
 442                         return -ENOENT;
 443
 444         } while (*t != ':');
 445
 446         t++;
 447
 448         if (*t) {
 449                 t += strspn(t, " \t");
 450
 451                 /* Also skip zeros, because when this is used for
 452                  * capabilities, we don't want the zeros. This way the
 453                  * same capability set always maps to the same string,
 454                  * irrespective of the total capability set size. For
 455                  * other numbers it shouldn't matter. */
 456                 t += strspn(t, "0");
 457                 /* Back off one char if there's nothing but whitespace
 458                    and zeros */
 459                 if (!*t || isspace(*t))
 460                         t--;
 461         }
 462
 463         len = strcspn(t, terminator);
 464
 465         f = strndup(t, len);
 466         if (!f)
 467                 return -ENOMEM;
 468
 469         *field = f;
 470         return 0;
 471 }
 472
 473 DIR *xopendirat(int fd, const char *name, int flags) {
 474         int nfd;
 475         DIR *d;
 476
 477         assert(!(flags & O_CREAT));
 478
 479         nfd = openat(fd, name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|flags, 0);
 480         if (nfd < 0)
 481                 return NULL;
 482
 483         d = fdopendir(nfd);
 484         if (!d) {
 485                 safe_close(nfd);
 486                 return NULL;
 487         }
 488
 489         return d;
 490 }
 491
 492 static int search_and_fopen_internal(const char *path, const char *mode, const char *root, char **search, FILE **_f) {
 493         char **i;
 494
 495         assert(path);
 496         assert(mode);
 497         assert(_f);
 498
 499         if (!path_strv_resolve_uniq(search, root))
 500                 return -ENOMEM;
 501
 502         STRV_FOREACH(i, search) {
 503                 _cleanup_free_ char *p = NULL;
 504                 FILE *f;
 505
 506                 if (root)
 507                         p = strjoin(root, *i, "/", path);
 508                 else
 509                         p = strjoin(*i, "/", path);
 510                 if (!p)
 511                         return -ENOMEM;
 512
 513                 f = fopen(p, mode);
 514                 if (f) {
 515                         *_f = f;
 516                         return 0;
 517                 }
 518
 519                 if (errno != ENOENT)
 520                         return -errno;
 521         }
 522
 523         return -ENOENT;
 524 }
 525
 526 int search_and_fopen(const char *path, const char *mode, const char *root, const char **search, FILE **_f) {
 527         _cleanup_strv_free_ char **copy = NULL;
 528
 529         assert(path);
 530         assert(mode);
 531         assert(_f);
 532
 533         if (path_is_absolute(path)) {
 534                 FILE *f;
 535
 536                 f = fopen(path, mode);
 537                 if (f) {
 538                         *_f = f;
 539                         return 0;
 540                 }
 541
 542                 return -errno;
 543         }
 544
 545         copy = strv_copy((char**) search);
 546         if (!copy)
 547                 return -ENOMEM;
 548
 549         return search_and_fopen_internal(path, mode, root, copy, _f);
 550 }
 551
 552 int search_and_fopen_nulstr(const char *path, const char *mode, const char *root, const char *search, FILE **_f) {
 553         _cleanup_strv_free_ char **s = NULL;
 554
 555         if (path_is_absolute(path)) {
 556                 FILE *f;
 557
 558                 f = fopen(path, mode);
 559                 if (f) {
 560                         *_f = f;
 561                         return 0;
 562                 }
 563
 564                 return -errno;
 565         }
 566
 567         s = strv_split_nulstr(search);
 568         if (!s)
 569                 return -ENOMEM;
 570
 571         return search_and_fopen_internal(path, mode, root, s, _f);
 572 }
 573
 574 int fflush_and_check(FILE *f) {
 575         assert(f);
 576
 577         errno = 0;
 578         fflush(f);
 579
 580         if (ferror(f))
 581                 return errno > 0 ? -errno : -EIO;
 582
 583         return 0;
 584 }
 585
 586 int fflush_sync_and_check(FILE *f) {
 587         int r;
 588
 589         assert(f);
 590
 591         r = fflush_and_check(f);
 592         if (r < 0)
 593                 return r;
 594
 595         if (fsync(fileno(f)) < 0)
 596                 return -errno;
 597
 598         r = fsync_directory_of_file(fileno(f));
 599         if (r < 0)
 600                 return r;
 601
 602         return 0;
 603 }
 604
 605 int write_timestamp_file_atomic(const char *fn, usec_t n) {
 606         char ln[DECIMAL_STR_MAX(n)+2];
 607
 608         /* Creates a "timestamp" file, that contains nothing but a
 609          * usec_t timestamp, formatted in ASCII. */
 610
 611         if (n <= 0 || n >= USEC_INFINITY)
 612                 return -ERANGE;
 613
 614         xsprintf(ln, USEC_FMT "\n", n);
 615
 616         return write_string_file(fn, ln, WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
 617 }
 618
 619 int read_timestamp_file(const char *fn, usec_t *ret) {
 620         _cleanup_free_ char *ln = NULL;
 621         uint64_t t;
 622         int r;
 623
 624         r = read_one_line_file(fn, &ln);
 625         if (r < 0)
 626                 return r;
 627
 628         r = safe_atou64(ln, &t);
 629         if (r < 0)
 630                 return r;
 631
 632         if (t <= 0 || t >= (uint64_t) USEC_INFINITY)
 633                 return -ERANGE;
 634
 635         *ret = (usec_t) t;
 636         return 0;
 637 }
 638
 639 int fputs_with_space(FILE *f, const char *s, const char *separator, bool *space) {
 640         int r;
 641
 642         assert(s);
 643
 644         /* Outputs the specified string with fputs(), but optionally prefixes it with a separator. The *space parameter
 645          * when specified shall initially point to a boolean variable initialized to false. It is set to true after the
 646          * first invocation. This call is supposed to be use in loops, where a separator shall be inserted between each
 647          * element, but not before the first one. */
 648
 649         if (!f)
 650                 f = stdout;
 651
 652         if (space) {
 653                 if (!separator)
 654                         separator = " ";
 655
 656                 if (*space) {
 657                         r = fputs(separator, f);
 658                         if (r < 0)
 659                                 return r;
 660                 }
 661
 662                 *space = true;
 663         }
 664
 665         return fputs(s, f);
 666 }
 667
 668 /* A bitmask of the EOL markers we know */
 669 typedef enum EndOfLineMarker {
 670         EOL_NONE     = 0,
 671         EOL_ZERO     = 1 << 0,  /* \0 (aka NUL) */
 672         EOL_TEN      = 1 << 1,  /* \n (aka NL, aka LF)  */
 673         EOL_THIRTEEN = 1 << 2,  /* \r (aka CR)  */
 674 } EndOfLineMarker;
 675
 676 static EndOfLineMarker categorize_eol(char c, ReadLineFlags flags) {
 677
 678         if (!IN_SET(flags, READ_LINE_ONLY_NUL)) {
 679                 if (c == '\n')
 680                         return EOL_TEN;
 681                 if (c == '\r')
 682                         return EOL_THIRTEEN;
 683         }
 684
 685         if (c == '\0')
 686                 return EOL_ZERO;
 687
 688         return EOL_NONE;
 689 }
 690
 691 DEFINE_TRIVIAL_CLEANUP_FUNC(FILE*, funlockfile);
 692
 693 int read_line_full(FILE *f, size_t limit, ReadLineFlags flags, char **ret) {
 694         size_t n = 0, allocated = 0, count = 0;
 695         _cleanup_free_ char *buffer = NULL;
 696         int r;
 697
 698         assert(f);
 699
 700         /* Something like a bounded version of getline().
 701          *
 702          * Considers EOF, \n, \r and \0 end of line delimiters (or combinations of these), and does not include these
 703          * delimiters in the string returned. Specifically, recognizes the following combinations of markers as line
 704          * endings:
 705          *
 706          *     • \n        (UNIX)
 707          *     • \r        (old MacOS)
 708          *     • \0        (C strings)
 709          *     • \n\0
 710          *     • \r\0
 711          *     • \r\n      (Windows)
 712          *     • \n\r
 713          *     • \r\n\0
 714          *     • \n\r\0
 715          *
 716          * Returns the number of bytes read from the files (i.e. including delimiters — this hence usually differs from
 717          * the number of characters in the returned string). When EOF is hit, 0 is returned.
 718          *
 719          * The input parameter limit is the maximum numbers of characters in the returned string, i.e. excluding
 720          * delimiters. If the limit is hit we fail and return -ENOBUFS.
 721          *
 722          * If a line shall be skipped ret may be initialized as NULL. */
 723
 724         if (ret) {
 725                 if (!GREEDY_REALLOC(buffer, allocated, 1))
 726                         return -ENOMEM;
 727         }
 728
 729         {
 730                 _unused_ _cleanup_(funlockfilep) FILE *flocked = f;
 731                 EndOfLineMarker previous_eol = EOL_NONE;
 732                 flockfile(f);
 733
 734                 for (;;) {
 735                         EndOfLineMarker eol;
 736                         char c;
 737
 738                         if (n >= limit)
 739                                 return -ENOBUFS;
 740
 741                         if (count >= INT_MAX) /* We couldn't return the counter anymore as "int", hence refuse this */
 742                                 return -ENOBUFS;
 743
 744                         r = safe_fgetc(f, &c);
 745                         if (r < 0)
 746                                 return r;
 747                         if (r == 0) /* EOF is definitely EOL */
 748                                 break;
 749
 750                         eol = categorize_eol(c, flags);
 751
 752                         if (FLAGS_SET(previous_eol, EOL_ZERO) ||
 753                             (eol == EOL_NONE && previous_eol != EOL_NONE) ||
 754                             (eol != EOL_NONE && (previous_eol & eol) != 0)) {
 755                                 /* Previous char was a NUL? This is not an EOL, but the previous char was? This type of
 756                                  * EOL marker has been seen right before?  In either of these three cases we are
 757                                  * done. But first, let's put this character back in the queue. (Note that we have to
 758                                  * cast this to (unsigned char) here as ungetc() expects a positive 'int', and if we
 759                                  * are on an architecture where 'char' equals 'signed char' we need to ensure we don't
 760                                  * pass a negative value here. That said, to complicate things further ungetc() is
 761                                  * actually happy with most negative characters and implicitly casts them back to
 762                                  * positive ones as needed, except for \xff (aka -1, aka EOF), which it refuses. What a
 763                                  * godawful API!) */
 764                                 assert_se(ungetc((unsigned char) c, f) != EOF);
 765                                 break;
 766                         }
 767
 768                         count++;
 769
 770                         if (eol != EOL_NONE) {
 771                                 previous_eol |= eol;
 772                                 continue;
 773                         }
 774
 775                         if (ret) {
 776                                 if (!GREEDY_REALLOC(buffer, allocated, n + 2))
 777                                         return -ENOMEM;
 778
 779                                 buffer[n] = c;
 780                         }
 781
 782                         n++;
 783                 }
 784         }
 785
 786         if (ret) {
 787                 buffer[n] = 0;
 788
 789                 *ret = TAKE_PTR(buffer);
 790         }
 791
 792         return (int) count;
 793 }
 794
 795 int safe_fgetc(FILE *f, char *ret) {
 796         int k;
 797
 798         assert(f);
 799
 800         /* A safer version of plain fgetc(): let's propagate the error that happened while reading as such, and
 801          * separate the EOF condition from the byte read, to avoid those confusion signed/unsigned issues fgetc()
 802          * has. */
 803
 804         errno = 0;
 805         k = fgetc(f);
 806         if (k == EOF) {
 807                 if (ferror(f))
 808                         return errno > 0 ? -errno : -EIO;
 809
 810                 if (ret)
 811                         *ret = 0;
 812
 813                 return 0;
 814         }
 815
 816         if (ret)
 817                 *ret = k;
 818
 819         return 1;
 820 }