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 "hexdecoct.h"
  21 #include "log.h"
  22 #include "macro.h"
  23 #include "missing.h"
  24 #include "mkdir.h"
  25 #include "parse-util.h"
  26 #include "path-util.h"
  27 #include "stdio-util.h"
  28 #include "string-util.h"
  29 #include "tmpfile-util.h"
  30
  31 #define READ_FULL_BYTES_MAX (4U*1024U*1024U)
  32
  33 int fopen_unlocked(const char *path, const char *options, FILE **ret) {
  34         assert(ret);
  35
  36         FILE *f = fopen(path, options);
  37         if (!f)
  38                 return -errno;
  39
  40         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  41
  42         *ret = f;
  43         return 0;
  44 }
  45
  46 int fdopen_unlocked(int fd, const char *options, FILE **ret) {
  47         assert(ret);
  48
  49         FILE *f = fdopen(fd, options);
  50         if (!f)
  51                 return -errno;
  52
  53         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  54
  55         *ret = f;
  56         return 0;
  57 }
  58
  59 FILE* open_memstream_unlocked(char **ptr, size_t *sizeloc) {
  60         FILE *f = open_memstream(ptr, sizeloc);
  61         if (!f)
  62                 return NULL;
  63
  64         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  65
  66         return f;
  67 }
  68
  69 FILE* fmemopen_unlocked(void *buf, size_t size, const char *mode) {
  70         FILE *f = fmemopen(buf, size, mode);
  71         if (!f)
  72                 return NULL;
  73
  74         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
  75
  76         return f;
  77 }
  78
  79 int write_string_stream_ts(
  80                 FILE *f,
  81                 const char *line,
  82                 WriteStringFileFlags flags,
  83                 struct timespec *ts) {
  84
  85         bool needs_nl;
  86         int r;
  87
  88         assert(f);
  89         assert(line);
  90
  91         if (ferror(f))
  92                 return -EIO;
  93
  94         needs_nl = !(flags & WRITE_STRING_FILE_AVOID_NEWLINE) && !endswith(line, "\n");
  95
  96         if (needs_nl && (flags & WRITE_STRING_FILE_DISABLE_BUFFER)) {
  97                 /* If STDIO buffering was disabled, then let's append the newline character to the string itself, so
  98                  * that the write goes out in one go, instead of two */
  99
 100                 line = strjoina(line, "\n");
 101                 needs_nl = false;
 102         }
 103
 104         if (fputs(line, f) == EOF)
 105                 return -errno;
 106
 107         if (needs_nl)
 108                 if (fputc('\n', f) == EOF)
 109                         return -errno;
 110
 111         if (flags & WRITE_STRING_FILE_SYNC)
 112                 r = fflush_sync_and_check(f);
 113         else
 114                 r = fflush_and_check(f);
 115         if (r < 0)
 116                 return r;
 117
 118         if (ts) {
 119                 struct timespec twice[2] = {*ts, *ts};
 120
 121                 if (futimens(fileno(f), twice) < 0)
 122                         return -errno;
 123         }
 124
 125         return 0;
 126 }
 127
 128 static int write_string_file_atomic(
 129                 const char *fn,
 130                 const char *line,
 131                 WriteStringFileFlags flags,
 132                 struct timespec *ts) {
 133
 134         _cleanup_fclose_ FILE *f = NULL;
 135         _cleanup_free_ char *p = NULL;
 136         int r;
 137
 138         assert(fn);
 139         assert(line);
 140
 141         r = fopen_temporary(fn, &f, &p);
 142         if (r < 0)
 143                 return r;
 144
 145         (void) fchmod_umask(fileno(f), 0644);
 146
 147         r = write_string_stream_ts(f, line, flags, ts);
 148         if (r < 0)
 149                 goto fail;
 150
 151         if (rename(p, fn) < 0) {
 152                 r = -errno;
 153                 goto fail;
 154         }
 155
 156         return 0;
 157
 158 fail:
 159         (void) unlink(p);
 160         return r;
 161 }
 162
 163 int write_string_file_ts(
 164                 const char *fn,
 165                 const char *line,
 166                 WriteStringFileFlags flags,
 167                 struct timespec *ts) {
 168
 169         _cleanup_fclose_ FILE *f = NULL;
 170         int q, r;
 171
 172         assert(fn);
 173         assert(line);
 174
 175         /* We don't know how to verify whether the file contents was already on-disk. */
 176         assert(!((flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE) && (flags & WRITE_STRING_FILE_SYNC)));
 177
 178         if (flags & WRITE_STRING_FILE_MKDIR_0755) {
 179                 r = mkdir_parents(fn, 0755);
 180                 if (r < 0)
 181                         return r;
 182         }
 183
 184         if (flags & WRITE_STRING_FILE_ATOMIC) {
 185                 assert(flags & WRITE_STRING_FILE_CREATE);
 186
 187                 r = write_string_file_atomic(fn, line, flags, ts);
 188                 if (r < 0)
 189                         goto fail;
 190
 191                 return r;
 192         } else
 193                 assert(!ts);
 194
 195         if (flags & WRITE_STRING_FILE_CREATE) {
 196                 r = fopen_unlocked(fn, "we", &f);
 197                 if (r < 0)
 198                         goto fail;
 199         } else {
 200                 int fd;
 201
 202                 /* We manually build our own version of fopen(..., "we") that
 203                  * works without O_CREAT */
 204                 fd = open(fn, O_WRONLY|O_CLOEXEC|O_NOCTTY | ((flags & WRITE_STRING_FILE_NOFOLLOW) ? O_NOFOLLOW : 0));
 205                 if (fd < 0) {
 206                         r = -errno;
 207                         goto fail;
 208                 }
 209
 210                 r = fdopen_unlocked(fd, "w", &f);
 211                 if (r < 0) {
 212                         safe_close(fd);
 213                         goto fail;
 214                 }
 215         }
 216
 217         if (flags & WRITE_STRING_FILE_DISABLE_BUFFER)
 218                 setvbuf(f, NULL, _IONBF, 0);
 219
 220         r = write_string_stream_ts(f, line, flags, ts);
 221         if (r < 0)
 222                 goto fail;
 223
 224         return 0;
 225
 226 fail:
 227         if (!(flags & WRITE_STRING_FILE_VERIFY_ON_FAILURE))
 228                 return r;
 229
 230         f = safe_fclose(f);
 231
 232         /* OK, the operation failed, but let's see if the right
 233          * contents in place already. If so, eat up the error. */
 234
 235         q = verify_file(fn, line, !(flags & WRITE_STRING_FILE_AVOID_NEWLINE));
 236         if (q <= 0)
 237                 return r;
 238
 239         return 0;
 240 }
 241
 242 int write_string_filef(
 243                 const char *fn,
 244                 WriteStringFileFlags flags,
 245                 const char *format, ...) {
 246
 247         _cleanup_free_ char *p = NULL;
 248         va_list ap;
 249         int r;
 250
 251         va_start(ap, format);
 252         r = vasprintf(&p, format, ap);
 253         va_end(ap);
 254
 255         if (r < 0)
 256                 return -ENOMEM;
 257
 258         return write_string_file(fn, p, flags);
 259 }
 260
 261 int read_one_line_file(const char *fn, char **line) {
 262         _cleanup_fclose_ FILE *f = NULL;
 263         int r;
 264
 265         assert(fn);
 266         assert(line);
 267
 268         r = fopen_unlocked(fn, "re", &f);
 269         if (r < 0)
 270                 return r;
 271
 272         return read_line(f, LONG_LINE_MAX, line);
 273 }
 274
 275 int verify_file(const char *fn, const char *blob, bool accept_extra_nl) {
 276         _cleanup_fclose_ FILE *f = NULL;
 277         _cleanup_free_ char *buf = NULL;
 278         size_t l, k;
 279         int r;
 280
 281         assert(fn);
 282         assert(blob);
 283
 284         l = strlen(blob);
 285
 286         if (accept_extra_nl && endswith(blob, "\n"))
 287                 accept_extra_nl = false;
 288
 289         buf = malloc(l + accept_extra_nl + 1);
 290         if (!buf)
 291                 return -ENOMEM;
 292
 293         r = fopen_unlocked(fn, "re", &f);
 294         if (r < 0)
 295                 return r;
 296
 297         /* We try to read one byte more than we need, so that we know whether we hit eof */
 298         errno = 0;
 299         k = fread(buf, 1, l + accept_extra_nl + 1, f);
 300         if (ferror(f))
 301                 return errno_or_else(EIO);
 302
 303         if (k != l && k != l + accept_extra_nl)
 304                 return 0;
 305         if (memcmp(buf, blob, l) != 0)
 306                 return 0;
 307         if (k > l && buf[l] != '\n')
 308                 return 0;
 309
 310         return 1;
 311 }
 312
 313 int read_full_stream_full(
 314                 FILE *f,
 315                 const char *filename,
 316                 ReadFullFileFlags flags,
 317                 char **ret_contents,
 318                 size_t *ret_size) {
 319
 320         _cleanup_free_ char *buf = NULL;
 321         struct stat st;
 322         size_t n, n_next, l;
 323         int fd, r;
 324
 325         assert(f);
 326         assert(ret_contents);
 327         assert(!FLAGS_SET(flags, READ_FULL_FILE_UNBASE64 | READ_FULL_FILE_UNHEX));
 328         assert(!(flags & (READ_FULL_FILE_UNBASE64 | READ_FULL_FILE_UNHEX)) || ret_size);
 329
 330         n_next = LINE_MAX; /* Start size */
 331
 332         fd = fileno(f);
 333         if (fd >= 0) { /* If the FILE* object is backed by an fd (as opposed to memory or such, see fmemopen(), let's
 334                         * optimize our buffering) */
 335
 336                 if (fstat(fd, &st) < 0)
 337                         return -errno;
 338
 339                 if (S_ISREG(st.st_mode)) {
 340
 341                         /* Safety check */
 342                         if (st.st_size > READ_FULL_BYTES_MAX)
 343                                 return -E2BIG;
 344
 345                         /* Start with the right file size, but be prepared for files from /proc which generally report a file
 346                          * size of 0. Note that we increase the size to read here by one, so that the first read attempt
 347                          * already makes us notice the EOF. */
 348                         if (st.st_size > 0)
 349                                 n_next = st.st_size + 1;
 350
 351                         if (flags & READ_FULL_FILE_SECURE)
 352                                 (void) warn_file_is_world_accessible(filename, &st, NULL, 0);
 353                 }
 354         }
 355
 356         n = l = 0;
 357         for (;;) {
 358                 char *t;
 359                 size_t k;
 360
 361                 if (flags & READ_FULL_FILE_SECURE) {
 362                         t = malloc(n_next + 1);
 363                         if (!t) {
 364                                 r = -ENOMEM;
 365                                 goto finalize;
 366                         }
 367                         memcpy_safe(t, buf, n);
 368                         explicit_bzero_safe(buf, n);
 369                         buf = mfree(buf);
 370                 } else {
 371                         t = realloc(buf, n_next + 1);
 372                         if (!t)
 373                                 return -ENOMEM;
 374                 }
 375
 376                 buf = t;
 377                 n = n_next;
 378
 379                 errno = 0;
 380                 k = fread(buf + l, 1, n - l, f);
 381                 if (k > 0)
 382                         l += k;
 383
 384                 if (ferror(f)) {
 385                         r = errno_or_else(EIO);
 386                         goto finalize;
 387                 }
 388
 389                 if (feof(f))
 390                         break;
 391
 392                 /* We aren't expecting fread() to return a short read outside
 393                  * of (error && eof), assert buffer is full and enlarge buffer.
 394                  */
 395                 assert(l == n);
 396
 397                 /* Safety check */
 398                 if (n >= READ_FULL_BYTES_MAX) {
 399                         r = -E2BIG;
 400                         goto finalize;
 401                 }
 402
 403                 n_next = MIN(n * 2, READ_FULL_BYTES_MAX);
 404         }
 405
 406         if (flags & (READ_FULL_FILE_UNBASE64 | READ_FULL_FILE_UNHEX)) {
 407                 buf[l++] = 0;
 408                 if (flags & READ_FULL_FILE_UNBASE64)
 409                         r = unbase64mem_full(buf, l, flags & READ_FULL_FILE_SECURE, (void **) ret_contents, ret_size);
 410                 else
 411                         r = unhexmem_full(buf, l, flags & READ_FULL_FILE_SECURE, (void **) ret_contents, ret_size);
 412                 goto finalize;
 413         }
 414
 415         if (!ret_size) {
 416                 /* Safety check: if the caller doesn't want to know the size of what we just read it will rely on the
 417                  * trailing NUL byte. But if there's an embedded NUL byte, then we should refuse operation as otherwise
 418                  * there'd be ambiguity about what we just read. */
 419
 420                 if (memchr(buf, 0, l)) {
 421                         r = -EBADMSG;
 422                         goto finalize;
 423                 }
 424         }
 425
 426         buf[l] = 0;
 427         *ret_contents = TAKE_PTR(buf);
 428
 429         if (ret_size)
 430                 *ret_size = l;
 431
 432         return 0;
 433
 434 finalize:
 435         if (flags & READ_FULL_FILE_SECURE)
 436                 explicit_bzero_safe(buf, n);
 437
 438         return r;
 439 }
 440
 441 int read_full_file_full(const char *filename, ReadFullFileFlags flags, char **contents, size_t *size) {
 442         _cleanup_fclose_ FILE *f = NULL;
 443         int r;
 444
 445         assert(filename);
 446         assert(contents);
 447
 448         r = fopen_unlocked(filename, "re", &f);
 449         if (r < 0)
 450                 return r;
 451
 452         return read_full_stream_full(f, filename, flags, contents, size);
 453 }
 454
 455 int executable_is_script(const char *path, char **interpreter) {
 456         _cleanup_free_ char *line = NULL;
 457         size_t len;
 458         char *ans;
 459         int r;
 460
 461         assert(path);
 462
 463         r = read_one_line_file(path, &line);
 464         if (r == -ENOBUFS) /* First line overly long? if so, then it's not a script */
 465                 return 0;
 466         if (r < 0)
 467                 return r;
 468
 469         if (!startswith(line, "#!"))
 470                 return 0;
 471
 472         ans = strstrip(line + 2);
 473         len = strcspn(ans, " \t");
 474
 475         if (len == 0)
 476                 return 0;
 477
 478         ans = strndup(ans, len);
 479         if (!ans)
 480                 return -ENOMEM;
 481
 482         *interpreter = ans;
 483         return 1;
 484 }
 485
 486 /**
 487  * Retrieve one field from a file like /proc/self/status.  pattern
 488  * should not include whitespace or the delimiter (':'). pattern matches only
 489  * the beginning of a line. Whitespace before ':' is skipped. Whitespace and
 490  * zeros after the ':' will be skipped. field must be freed afterwards.
 491  * terminator specifies the terminating characters of the field value (not
 492  * included in the value).
 493  */
 494 int get_proc_field(const char *filename, const char *pattern, const char *terminator, char **field) {
 495         _cleanup_free_ char *status = NULL;
 496         char *t, *f;
 497         size_t len;
 498         int r;
 499
 500         assert(terminator);
 501         assert(filename);
 502         assert(pattern);
 503         assert(field);
 504
 505         r = read_full_file(filename, &status, NULL);
 506         if (r < 0)
 507                 return r;
 508
 509         t = status;
 510
 511         do {
 512                 bool pattern_ok;
 513
 514                 do {
 515                         t = strstr(t, pattern);
 516                         if (!t)
 517                                 return -ENOENT;
 518
 519                         /* Check that pattern occurs in beginning of line. */
 520                         pattern_ok = (t == status || t[-1] == '\n');
 521
 522                         t += strlen(pattern);
 523
 524                 } while (!pattern_ok);
 525
 526                 t += strspn(t, " \t");
 527                 if (!*t)
 528                         return -ENOENT;
 529
 530         } while (*t != ':');
 531
 532         t++;
 533
 534         if (*t) {
 535                 t += strspn(t, " \t");
 536
 537                 /* Also skip zeros, because when this is used for
 538                  * capabilities, we don't want the zeros. This way the
 539                  * same capability set always maps to the same string,
 540                  * irrespective of the total capability set size. For
 541                  * other numbers it shouldn't matter. */
 542                 t += strspn(t, "0");
 543                 /* Back off one char if there's nothing but whitespace
 544                    and zeros */
 545                 if (!*t || isspace(*t))
 546                         t--;
 547         }
 548
 549         len = strcspn(t, terminator);
 550
 551         f = strndup(t, len);
 552         if (!f)
 553                 return -ENOMEM;
 554
 555         *field = f;
 556         return 0;
 557 }
 558
 559 DIR *xopendirat(int fd, const char *name, int flags) {
 560         int nfd;
 561         DIR *d;
 562
 563         assert(!(flags & O_CREAT));
 564
 565         nfd = openat(fd, name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|flags, 0);
 566         if (nfd < 0)
 567                 return NULL;
 568
 569         d = fdopendir(nfd);
 570         if (!d) {
 571                 safe_close(nfd);
 572                 return NULL;
 573         }
 574
 575         return d;
 576 }
 577
 578 static int search_and_fopen_internal(const char *path, const char *mode, const char *root, char **search, FILE **_f) {
 579         char **i;
 580
 581         assert(path);
 582         assert(mode);
 583         assert(_f);
 584
 585         if (!path_strv_resolve_uniq(search, root))
 586                 return -ENOMEM;
 587
 588         STRV_FOREACH(i, search) {
 589                 _cleanup_free_ char *p = NULL;
 590                 FILE *f;
 591
 592                 p = path_join(root, *i, path);
 593                 if (!p)
 594                         return -ENOMEM;
 595
 596                 f = fopen(p, mode);
 597                 if (f) {
 598                         *_f = f;
 599                         return 0;
 600                 }
 601
 602                 if (errno != ENOENT)
 603                         return -errno;
 604         }
 605
 606         return -ENOENT;
 607 }
 608
 609 int search_and_fopen(const char *path, const char *mode, const char *root, const char **search, FILE **_f) {
 610         _cleanup_strv_free_ char **copy = NULL;
 611
 612         assert(path);
 613         assert(mode);
 614         assert(_f);
 615
 616         if (path_is_absolute(path)) {
 617                 FILE *f;
 618
 619                 f = fopen(path, mode);
 620                 if (f) {
 621                         *_f = f;
 622                         return 0;
 623                 }
 624
 625                 return -errno;
 626         }
 627
 628         copy = strv_copy((char**) search);
 629         if (!copy)
 630                 return -ENOMEM;
 631
 632         return search_and_fopen_internal(path, mode, root, copy, _f);
 633 }
 634
 635 int search_and_fopen_nulstr(const char *path, const char *mode, const char *root, const char *search, FILE **_f) {
 636         _cleanup_strv_free_ char **s = NULL;
 637
 638         if (path_is_absolute(path)) {
 639                 FILE *f;
 640
 641                 f = fopen(path, mode);
 642                 if (f) {
 643                         *_f = f;
 644                         return 0;
 645                 }
 646
 647                 return -errno;
 648         }
 649
 650         s = strv_split_nulstr(search);
 651         if (!s)
 652                 return -ENOMEM;
 653
 654         return search_and_fopen_internal(path, mode, root, s, _f);
 655 }
 656
 657 int fflush_and_check(FILE *f) {
 658         assert(f);
 659
 660         errno = 0;
 661         fflush(f);
 662
 663         if (ferror(f))
 664                 return errno_or_else(EIO);
 665
 666         return 0;
 667 }
 668
 669 int fflush_sync_and_check(FILE *f) {
 670         int r;
 671
 672         assert(f);
 673
 674         r = fflush_and_check(f);
 675         if (r < 0)
 676                 return r;
 677
 678         if (fsync(fileno(f)) < 0)
 679                 return -errno;
 680
 681         r = fsync_directory_of_file(fileno(f));
 682         if (r < 0)
 683                 return r;
 684
 685         return 0;
 686 }
 687
 688 int write_timestamp_file_atomic(const char *fn, usec_t n) {
 689         char ln[DECIMAL_STR_MAX(n)+2];
 690
 691         /* Creates a "timestamp" file, that contains nothing but a
 692          * usec_t timestamp, formatted in ASCII. */
 693
 694         if (n <= 0 || n >= USEC_INFINITY)
 695                 return -ERANGE;
 696
 697         xsprintf(ln, USEC_FMT "\n", n);
 698
 699         return write_string_file(fn, ln, WRITE_STRING_FILE_CREATE|WRITE_STRING_FILE_ATOMIC);
 700 }
 701
 702 int read_timestamp_file(const char *fn, usec_t *ret) {
 703         _cleanup_free_ char *ln = NULL;
 704         uint64_t t;
 705         int r;
 706
 707         r = read_one_line_file(fn, &ln);
 708         if (r < 0)
 709                 return r;
 710
 711         r = safe_atou64(ln, &t);
 712         if (r < 0)
 713                 return r;
 714
 715         if (t <= 0 || t >= (uint64_t) USEC_INFINITY)
 716                 return -ERANGE;
 717
 718         *ret = (usec_t) t;
 719         return 0;
 720 }
 721
 722 int fputs_with_space(FILE *f, const char *s, const char *separator, bool *space) {
 723         int r;
 724
 725         assert(s);
 726
 727         /* Outputs the specified string with fputs(), but optionally prefixes it with a separator. The *space parameter
 728          * when specified shall initially point to a boolean variable initialized to false. It is set to true after the
 729          * first invocation. This call is supposed to be use in loops, where a separator shall be inserted between each
 730          * element, but not before the first one. */
 731
 732         if (!f)
 733                 f = stdout;
 734
 735         if (space) {
 736                 if (!separator)
 737                         separator = " ";
 738
 739                 if (*space) {
 740                         r = fputs(separator, f);
 741                         if (r < 0)
 742                                 return r;
 743                 }
 744
 745                 *space = true;
 746         }
 747
 748         return fputs(s, f);
 749 }
 750
 751 /* A bitmask of the EOL markers we know */
 752 typedef enum EndOfLineMarker {
 753         EOL_NONE     = 0,
 754         EOL_ZERO     = 1 << 0,  /* \0 (aka NUL) */
 755         EOL_TEN      = 1 << 1,  /* \n (aka NL, aka LF)  */
 756         EOL_THIRTEEN = 1 << 2,  /* \r (aka CR)  */
 757 } EndOfLineMarker;
 758
 759 static EndOfLineMarker categorize_eol(char c, ReadLineFlags flags) {
 760
 761         if (!IN_SET(flags, READ_LINE_ONLY_NUL)) {
 762                 if (c == '\n')
 763                         return EOL_TEN;
 764                 if (c == '\r')
 765                         return EOL_THIRTEEN;
 766         }
 767
 768         if (c == '\0')
 769                 return EOL_ZERO;
 770
 771         return EOL_NONE;
 772 }
 773
 774 DEFINE_TRIVIAL_CLEANUP_FUNC(FILE*, funlockfile);
 775
 776 int read_line_full(FILE *f, size_t limit, ReadLineFlags flags, char **ret) {
 777         size_t n = 0, allocated = 0, count = 0;
 778         _cleanup_free_ char *buffer = NULL;
 779         int r, tty = -1;
 780
 781         assert(f);
 782
 783         /* Something like a bounded version of getline().
 784          *
 785          * Considers EOF, \n, \r and \0 end of line delimiters (or combinations of these), and does not include these
 786          * delimiters in the string returned. Specifically, recognizes the following combinations of markers as line
 787          * endings:
 788          *
 789          *     • \n        (UNIX)
 790          *     • \r        (old MacOS)
 791          *     • \0        (C strings)
 792          *     • \n\0
 793          *     • \r\0
 794          *     • \r\n      (Windows)
 795          *     • \n\r
 796          *     • \r\n\0
 797          *     • \n\r\0
 798          *
 799          * Returns the number of bytes read from the files (i.e. including delimiters — this hence usually differs from
 800          * the number of characters in the returned string). When EOF is hit, 0 is returned.
 801          *
 802          * The input parameter limit is the maximum numbers of characters in the returned string, i.e. excluding
 803          * delimiters. If the limit is hit we fail and return -ENOBUFS.
 804          *
 805          * If a line shall be skipped ret may be initialized as NULL. */
 806
 807         if (ret) {
 808                 if (!GREEDY_REALLOC(buffer, allocated, 1))
 809                         return -ENOMEM;
 810         }
 811
 812         {
 813                 _unused_ _cleanup_(funlockfilep) FILE *flocked = f;
 814                 EndOfLineMarker previous_eol = EOL_NONE;
 815                 flockfile(f);
 816
 817                 for (;;) {
 818                         EndOfLineMarker eol;
 819                         char c;
 820
 821                         if (n >= limit)
 822                                 return -ENOBUFS;
 823
 824                         if (count >= INT_MAX) /* We couldn't return the counter anymore as "int", hence refuse this */
 825                                 return -ENOBUFS;
 826
 827                         r = safe_fgetc(f, &c);
 828                         if (r < 0)
 829                                 return r;
 830                         if (r == 0) /* EOF is definitely EOL */
 831                                 break;
 832
 833                         eol = categorize_eol(c, flags);
 834
 835                         if (FLAGS_SET(previous_eol, EOL_ZERO) ||
 836                             (eol == EOL_NONE && previous_eol != EOL_NONE) ||
 837                             (eol != EOL_NONE && (previous_eol & eol) != 0)) {
 838                                 /* Previous char was a NUL? This is not an EOL, but the previous char was? This type of
 839                                  * EOL marker has been seen right before?  In either of these three cases we are
 840                                  * done. But first, let's put this character back in the queue. (Note that we have to
 841                                  * cast this to (unsigned char) here as ungetc() expects a positive 'int', and if we
 842                                  * are on an architecture where 'char' equals 'signed char' we need to ensure we don't
 843                                  * pass a negative value here. That said, to complicate things further ungetc() is
 844                                  * actually happy with most negative characters and implicitly casts them back to
 845                                  * positive ones as needed, except for \xff (aka -1, aka EOF), which it refuses. What a
 846                                  * godawful API!) */
 847                                 assert_se(ungetc((unsigned char) c, f) != EOF);
 848                                 break;
 849                         }
 850
 851                         count++;
 852
 853                         if (eol != EOL_NONE) {
 854                                 /* If we are on a tty, we can't wait for more input. But we expect only
 855                                  * \n as the single EOL marker, so there is no need to wait. We check
 856                                  * this condition last to avoid isatty() check if not necessary. */
 857
 858                                 if (tty < 0)
 859                                         tty = isatty(fileno(f));
 860                                 if (tty > 0)
 861                                         break;
 862                         }
 863
 864                         if (eol != EOL_NONE) {
 865                                 previous_eol |= eol;
 866                                 continue;
 867                         }
 868
 869                         if (ret) {
 870                                 if (!GREEDY_REALLOC(buffer, allocated, n + 2))
 871                                         return -ENOMEM;
 872
 873                                 buffer[n] = c;
 874                         }
 875
 876                         n++;
 877                 }
 878         }
 879
 880         if (ret) {
 881                 buffer[n] = 0;
 882
 883                 *ret = TAKE_PTR(buffer);
 884         }
 885
 886         return (int) count;
 887 }
 888
 889 int safe_fgetc(FILE *f, char *ret) {
 890         int k;
 891
 892         assert(f);
 893
 894         /* A safer version of plain fgetc(): let's propagate the error that happened while reading as such, and
 895          * separate the EOF condition from the byte read, to avoid those confusion signed/unsigned issues fgetc()
 896          * has. */
 897
 898         errno = 0;
 899         k = fgetc(f);
 900         if (k == EOF) {
 901                 if (ferror(f))
 902                         return errno_or_else(EIO);
 903
 904                 if (ret)
 905                         *ret = 0;
 906
 907                 return 0;
 908         }
 909
 910         if (ret)
 911                 *ret = k;
 912
 913         return 1;
 914 }
 915
 916 int warn_file_is_world_accessible(const char *filename, struct stat *st, const char *unit, unsigned line) {
 917         struct stat _st;
 918
 919         if (!filename)
 920                 return 0;
 921
 922         if (!st) {
 923                 if (stat(filename, &_st) < 0)
 924                         return -errno;
 925                 st = &_st;
 926         }
 927
 928         if ((st->st_mode & S_IRWXO) == 0)
 929                 return 0;
 930
 931         if (unit)
 932                 log_syntax(unit, LOG_WARNING, filename, line, 0,
 933                            "%s has %04o mode that is too permissive, please adjust the ownership and access mode.",
 934                            filename, st->st_mode & 07777);
 935         else
 936                 log_warning("%s has %04o mode that is too permissive, please adjust the ownership and access mode.",
 937                             filename, st->st_mode & 07777);
 938         return 0;
 939 }