aboutsummaryrefslogtreecommitdiff
path: root/lib/xwrap.c
blob: 611bdb52037261857e67832c2cc62fac1d148330 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
/* xwrap.c - wrappers around existing library functions.
 *
 * Functions with the x prefix are wrappers that either succeed or kill the
 * program with an error message, but never return failure. They usually have
 * the same arguments and return value as the function they wrap.
 *
 * Copyright 2006 Rob Landley <rob@landley.net>
 */

#include "toys.h"

// strcpy and strncat with size checking. Size is the total space in "dest",
// including null terminator. Exit if there's not enough space for the string
// (including space for the null terminator), because silently truncating is
// still broken behavior. (And leaving the string unterminated is INSANE.)
void xstrncpy(char *dest, char *src, size_t size)
{
  if (strlen(src)+1 > size) error_exit("'%s' > %ld bytes", src, (long)size);
  strcpy(dest, src);
}

void xstrncat(char *dest, char *src, size_t size)
{
  long len = strlen(dest);

  if (len+strlen(src)+1 > size)
    error_exit("'%s%s' > %ld bytes", dest, src, (long)size);
  strcpy(dest+len, src);
}

// We replaced exit(), _exit(), and atexit() with xexit(), _xexit(), and
// sigatexit(). This gives _xexit() the option to siglongjmp(toys.rebound, 1)
// instead of exiting, lets xexit() report stdout flush failures to stderr
// and change the exit code to indicate error, lets our toys.exit function
// change happen for signal exit paths and lets us remove the functions
// after we've called them.

void _xexit(void)
{
  if (toys.rebound) siglongjmp(*toys.rebound, 1);

  _exit(toys.exitval);
}

void xexit(void)
{
  // Call toys.xexit functions in reverse order added.
  while (toys.xexit) {
    // This is typecasting xexit->arg to a function pointer,then calling it.
    // Using the invalid signal number 0 lets the signal handlers distinguish
    // an actual signal from a regular exit.
    ((void (*)(int))(toys.xexit->arg))(0);

    free(llist_pop(&toys.xexit));
  }
  if (fflush(NULL) || ferror(stdout))
    if (!toys.exitval) perror_msg("write");
  _xexit();
}

// Die unless we can allocate memory.
void *xmalloc(size_t size)
{
  void *ret = malloc(size);
  if (!ret) error_exit("xmalloc(%ld)", (long)size);

  return ret;
}

// Die unless we can allocate prezeroed memory.
void *xzalloc(size_t size)
{
  void *ret = xmalloc(size);
  memset(ret, 0, size);
  return ret;
}

// Die unless we can change the size of an existing allocation, possibly
// moving it.  (Notice different arguments from libc function.)
void *xrealloc(void *ptr, size_t size)
{
  ptr = realloc(ptr, size);
  if (!ptr) error_exit("xrealloc");

  return ptr;
}

// Die unless we can allocate a copy of this many bytes of string.
char *xstrndup(char *s, size_t n)
{
  char *ret = strndup(s, ++n);

  if (!ret) error_exit("xstrndup");
  ret[--n] = 0;

  return ret;
}

// Die unless we can allocate a copy of this string.
char *xstrdup(char *s)
{
  return xstrndup(s, strlen(s));
}

void *xmemdup(void *s, long len)
{
  void *ret = xmalloc(len);
  memcpy(ret, s, len);

  return ret;
}

// Die unless we can allocate enough space to sprintf() into.
char *xmprintf(char *format, ...)
{
  va_list va, va2;
  int len;
  char *ret;

  va_start(va, format);
  va_copy(va2, va);

  // How long is it?
  len = vsnprintf(0, 0, format, va);
  len++;
  va_end(va);

  // Allocate and do the sprintf()
  ret = xmalloc(len);
  vsnprintf(ret, len, format, va2);
  va_end(va2);

  return ret;
}

void xprintf(char *format, ...)
{
  va_list va;
  va_start(va, format);

  vprintf(format, va);
  va_end(va);
  if (fflush(stdout) || ferror(stdout)) perror_exit("write");
}

void xputs(char *s)
{
  if (EOF == puts(s) || fflush(stdout) || ferror(stdout)) perror_exit("write");
}

void xputc(char c)
{
  if (EOF == fputc(c, stdout) || fflush(stdout) || ferror(stdout))
    perror_exit("write");
}

void xflush(void)
{
  if (fflush(stdout) || ferror(stdout)) perror_exit("write");;
}

// This is called through the XVFORK macro because parent/child of vfork
// share a stack, so child returning from a function would stomp the return
// address parent would need. Solution: make vfork() an argument so processes
// diverge before function gets called.
pid_t __attribute__((noinline)) xvforkwrap(pid_t pid)
{
  if (pid == -1) perror_exit("vfork");

  // Signal to xexec() and friends that we vforked so can't recurse
  toys.stacktop = 0;

  return pid;
}

// Die unless we can exec argv[] (or run builtin command).  Note that anything
// with a path isn't a builtin, so /bin/sh won't match the builtin sh.
void xexec(char **argv)
{
  // Only recurse to builtin when we have multiplexer and !vfork context.
  if (CFG_TOYBOX && !CFG_TOYBOX_NORECURSE && toys.stacktop) toy_exec(argv);
  execvp(argv[0], argv);

  perror_msg("exec %s", argv[0]);
  toys.exitval = 127;
  if (!CFG_TOYBOX_FORK) _exit(toys.exitval);
  xexit();
}

// Spawn child process, capturing stdin/stdout.
// argv[]: command to exec. If null, child re-runs original program with
//         toys.stacktop zeroed.
// pipes[2]: stdin, stdout of new process, only allocated if zero on way in,
//           pass NULL to skip pipe allocation entirely.
// return: pid of child process
pid_t xpopen_both(char **argv, int *pipes)
{
  int cestnepasun[4], pid;

  // Make the pipes? Note this won't set either pipe to 0 because if fds are
  // allocated in order and if fd0 was free it would go to cestnepasun[0]
  if (pipes) {
    for (pid = 0; pid < 2; pid++) {
      if (pipes[pid] != 0) continue;
      if (pipe(cestnepasun+(2*pid))) perror_exit("pipe");
      pipes[pid] = cestnepasun[pid+1];
    }
  }

  // Child process.
  if (!(pid = CFG_TOYBOX_FORK ? xfork() : XVFORK())) {
    // Dance of the stdin/stdout redirection.
    if (pipes) {
      // if we had no stdin/out, pipe handles could overlap, so test for it
      // and free up potentially overlapping pipe handles before reuse
      if (pipes[1] != -1) close(cestnepasun[2]);
      if (pipes[0] != -1) {
        close(cestnepasun[1]);
        if (cestnepasun[0]) {
          dup2(cestnepasun[0], 0);
          close(cestnepasun[0]);
        }
      }
      if (pipes[1] != -1) {
        dup2(cestnepasun[3], 1);
        dup2(cestnepasun[3], 2);
        if (cestnepasun[3] > 2 || !cestnepasun[3]) close(cestnepasun[3]);
      }
    }
    if (argv) xexec(argv);

    // In fork() case, force recursion because we know it's us.
    if (CFG_TOYBOX_FORK) {
      toy_init(toys.which, toys.argv);
      toys.stacktop = 0;
      toys.which->toy_main();
      xexit();
    // In vfork() case, exec /proc/self/exe with high bit of first letter set
    // to tell main() we reentered.
    } else {
      char *s = "/proc/self/exe";

      // We did a nommu-friendly vfork but must exec to continue.
      // setting high bit of argv[0][0] to let new process know
      **toys.argv |= 0x80;
      execv(s, toys.argv);
      perror_msg_raw(s);

      _exit(127);
    }
  }

  // Parent process
  if (!CFG_TOYBOX_FORK) **toys.argv &= 0x7f;
  if (pipes) {
    if (pipes[0] != -1) close(cestnepasun[0]);
    if (pipes[1] != -1) close(cestnepasun[3]);
  }

  return pid;
}

// Wait for child process to exit, then return adjusted exit code.
int xwaitpid(pid_t pid)
{
  int status;

  while (-1 == waitpid(pid, &status, 0) && errno == EINTR);

  return WIFEXITED(status) ? WEXITSTATUS(status) : WTERMSIG(status)+127;
}

int xpclose_both(pid_t pid, int *pipes)
{
  if (pipes) {
    close(pipes[0]);
    close(pipes[1]);
  }

  return xwaitpid(pid);
}

// Wrapper to xpopen with a pipe for just one of stdin/stdout
pid_t xpopen(char **argv, int *pipe, int stdout)
{
  int pipes[2], pid;

  pipes[!stdout] = -1;
  pipes[!!stdout] = 0;
  pid = xpopen_both(argv, pipes);
  *pipe = pid ? pipes[!!stdout] : -1;

  return pid;
}

int xpclose(pid_t pid, int pipe)
{
  close(pipe);

  return xpclose_both(pid, 0);
}

// Call xpopen and wait for it to finish, keeping existing stdin/stdout.
int xrun(char **argv)
{
  return xpclose_both(xpopen_both(argv, 0), 0);
}

void xaccess(char *path, int flags)
{
  if (access(path, flags)) perror_exit("Can't access '%s'", path);
}

// Die unless we can delete a file.  (File must exist to be deleted.)
void xunlink(char *path)
{
  if (unlink(path)) perror_exit("unlink '%s'", path);
}

// Die unless we can open/create a file, returning file descriptor.
// The meaning of O_CLOEXEC is reversed (it defaults on, pass it to disable)
// and WARN_ONLY tells us not to exit.
int xcreate_stdio(char *path, int flags, int mode)
{
  int fd = open(path, (flags^O_CLOEXEC)&~WARN_ONLY, mode);

  if (fd == -1) ((mode&WARN_ONLY) ? perror_msg_raw : perror_exit_raw)(path);
  return fd;
}

// Die unless we can open a file, returning file descriptor.
int xopen_stdio(char *path, int flags)
{
  return xcreate_stdio(path, flags, 0);
}

void xpipe(int *pp)
{
  if (pipe(pp)) perror_exit("xpipe");
}

void xclose(int fd)
{
  if (close(fd)) perror_exit("xclose");
}

int xdup(int fd)
{
  if (fd != -1) {
    fd = dup(fd);
    if (fd == -1) perror_exit("xdup");
  }
  return fd;
}

// Move file descriptor above stdin/stdout/stderr, using /dev/null to consume
// old one. (We should never be called with stdin/stdout/stderr closed, but...)
int notstdio(int fd)
{
  if (fd<0) return fd;

  while (fd<3) {
    int fd2 = xdup(fd);

    close(fd);
    xopen_stdio("/dev/null", O_RDWR);
    fd = fd2;
  }

  return fd;
}

// Create a file but don't return stdin/stdout/stderr
int xcreate(char *path, int flags, int mode)
{
  return notstdio(xcreate_stdio(path, flags, mode));
}

// Open a file descriptor NOT in stdin/stdout/stderr
int xopen(char *path, int flags)
{
  return notstdio(xopen_stdio(path, flags));
}

// Open read only, treating "-" as a synonym for stdin, defaulting to warn only
int openro(char *path, int flags)
{
  if (!strcmp(path, "-")) return 0;

  return xopen(path, flags^WARN_ONLY);
}

// Open read only, treating "-" as a synonym for stdin.
int xopenro(char *path)
{
  return openro(path, O_RDONLY|WARN_ONLY);
}

FILE *xfdopen(int fd, char *mode)
{
  FILE *f = fdopen(fd, mode);

  if (!f) perror_exit("xfdopen");

  return f;
}

// Die unless we can open/create a file, returning FILE *.
FILE *xfopen(char *path, char *mode)
{
  FILE *f = fopen(path, mode);
  if (!f) perror_exit("No file %s", path);
  return f;
}

// Die if there's an error other than EOF.
size_t xread(int fd, void *buf, size_t len)
{
  ssize_t ret = read(fd, buf, len);
  if (ret < 0) perror_exit("xread");

  return ret;
}

void xreadall(int fd, void *buf, size_t len)
{
  if (len != readall(fd, buf, len)) perror_exit("xreadall");
}

// There's no xwriteall(), just xwrite().  When we read, there may or may not
// be more data waiting.  When we write, there is data and it had better go
// somewhere.

void xwrite(int fd, void *buf, size_t len)
{
  if (len != writeall(fd, buf, len)) perror_exit("xwrite");
}

// Die if lseek fails, probably due to being called on a pipe.

off_t xlseek(int fd, off_t offset, int whence)
{
  offset = lseek(fd, offset, whence);
  if (offset<0) perror_exit("lseek");

  return offset;
}

char *xgetcwd(void)
{
  char *buf = getcwd(NULL, 0);
  if (!buf) perror_exit("xgetcwd");

  return buf;
}

void xstat(char *path, struct stat *st)
{
  if(stat(path, st)) perror_exit("Can't stat %s", path);
}

// Cannonicalize path, even to file with one or more missing components at end.
// if exact, require last path component to exist
char *xabspath(char *path, int exact)
{
  struct string_list *todo, *done = 0;
  int try = 9999, dirfd = open("/", 0);;
  char *ret;

  // If this isn't an absolute path, start with cwd.
  if (*path != '/') {
    char *temp = xgetcwd();

    splitpath(path, splitpath(temp, &todo));
    free(temp);
  } else splitpath(path, &todo);

  // Iterate through path components
  while (todo) {
    struct string_list *new = llist_pop(&todo), **tail;
    ssize_t len;

    if (!try--) {
      errno = ELOOP;
      goto error;
    }

    // Removable path componenents.
    if (!strcmp(new->str, ".") || !strcmp(new->str, "..")) {
      int x = new->str[1];

      free(new);
      if (x) {
        if (done) free(llist_pop(&done));
        len = 0;
      } else continue;

    // Is this a symlink?
    } else len = readlinkat(dirfd, new->str, libbuf, sizeof(libbuf));

    if (len>4095) goto error;
    if (len<1) {
      int fd;
      char *s = "..";

      // For .. just move dirfd
      if (len) {
        // Not a symlink: add to linked list, move dirfd, fail if error
        if ((exact || todo) && errno != EINVAL) goto error;
        new->next = done;
        done = new;
        if (errno == EINVAL && !todo) break;
        s = new->str;
      }
      fd = openat(dirfd, s, 0);
      if (fd == -1 && (exact || todo || errno != ENOENT)) goto error;
      close(dirfd);
      dirfd = fd;
      continue;
    }

    // If this symlink is to an absolute path, discard existing resolved path
    libbuf[len] = 0;
    if (*libbuf == '/') {
      llist_traverse(done, free);
      done=0;
      close(dirfd);
      dirfd = open("/", 0);
    }
    free(new);

    // prepend components of new path. Note symlink to "/" will leave new NULL
    tail = splitpath(libbuf, &new);

    // symlink to "/" will return null and leave tail alone
    if (new) {
      *tail = todo;
      todo = new;
    }
  }
  close(dirfd);

  // At this point done has the path, in reverse order. Reverse list while
  // calculating buffer length.

  try = 2;
  while (done) {
    struct string_list *temp = llist_pop(&done);;

    if (todo) try++;
    try += strlen(temp->str);
    temp->next = todo;
    todo = temp;
  }

  // Assemble return buffer

  ret = xmalloc(try);
  *ret = '/';
  ret [try = 1] = 0;
  while (todo) {
    if (try>1) ret[try++] = '/';
    try = stpcpy(ret+try, todo->str) - ret;
    free(llist_pop(&todo));
  }

  return ret;

error:
  close(dirfd);
  llist_traverse(todo, free);
  llist_traverse(done, free);

  return NULL;
}

void xchdir(char *path)
{
  if (chdir(path)) error_exit("chdir '%s'", path);
}

void xchroot(char *path)
{
  if (chroot(path)) error_exit("chroot '%s'", path);
  xchdir("/");
}

struct passwd *xgetpwuid(uid_t uid)
{
  struct passwd *pwd = getpwuid(uid);
  if (!pwd) error_exit("bad uid %ld", (long)uid);
  return pwd;
}

struct group *xgetgrgid(gid_t gid)
{
  struct group *group = getgrgid(gid);

  if (!group) perror_exit("gid %ld", (long)gid);
  return group;
}

unsigned xgetuid(char *name)
{
  struct passwd *up = getpwnam(name);
  char *s = 0;
  long uid;

  if (up) return up->pw_uid;

  uid = estrtol(name, &s, 10);
  if (!errno && s && !*s && uid>=0 && uid<=UINT_MAX) return uid;

  error_exit("bad user '%s'", name);
}

unsigned xgetgid(char *name)
{
  struct group *gr = getgrnam(name);
  char *s = 0;
  long gid;

  if (gr) return gr->gr_gid;

  gid = estrtol(name, &s, 10);
  if (!errno && s && !*s && gid>=0 && gid<=UINT_MAX) return gid;

  error_exit("bad group '%s'", name);
}

struct passwd *xgetpwnam(char *name)
{
  struct passwd *up = getpwnam(name);

  if (!up) perror_exit("user '%s'", name);
  return up;
}

struct group *xgetgrnam(char *name)
{
  struct group *gr = getgrnam(name);

  if (!gr) perror_exit("group '%s'", name);
  return gr;
}

// setuid() can fail (for example, too many processes belonging to that user),
// which opens a security hole if the process continues as the original user.

void xsetuser(struct passwd *pwd)
{
  if (initgroups(pwd->pw_name, pwd->pw_gid) || setgid(pwd->pw_uid)
      || setuid(pwd->pw_uid)) perror_exit("xsetuser '%s'", pwd->pw_name);
}

// This can return null (meaning file not found).  It just won't return null
// for memory allocation reasons.
char *xreadlink(char *name)
{
  int len, size = 0;
  char *buf = 0;

  // Grow by 64 byte chunks until it's big enough.
  for(;;) {
    size +=64;
    buf = xrealloc(buf, size);
    len = readlink(name, buf, size);

    if (len<0) {
      free(buf);
      return 0;
    }
    if (len<size) {
      buf[len]=0;
      return buf;
    }
  }
}

char *xreadfile(char *name, char *buf, off_t len)
{
  if (!(buf = readfile(name, buf, len))) perror_exit("Bad '%s'", name);

  return buf;
}

// The data argument to ioctl() is actually long, but it's usually used as
// a pointer. If you need to feed in a number, do (void *)(long) typecast.
int xioctl(int fd, int request, void *data)
{
  int rc;

  errno = 0;
  rc = ioctl(fd, request, data);
  if (rc == -1 && errno) perror_exit("ioctl %x", request);

  return rc;
}

// Open a /var/run/NAME.pid file, dying if we can't write it or if it currently
// exists and is this executable.
void xpidfile(char *name)
{
  char pidfile[256], spid[32];
  int i, fd;
  pid_t pid;

  sprintf(pidfile, "/var/run/%s.pid", name);
  // Try three times to open the sucker.
  for (i=0; i<3; i++) {
    fd = open(pidfile, O_CREAT|O_EXCL|O_WRONLY, 0644);
    if (fd != -1) break;

    // If it already existed, read it.  Loop for race condition.
    fd = open(pidfile, O_RDONLY);
    if (fd == -1) continue;

    // Is the old program still there?
    spid[xread(fd, spid, sizeof(spid)-1)] = 0;
    close(fd);
    pid = atoi(spid);
    if (pid < 1 || (kill(pid, 0) && errno == ESRCH)) unlink(pidfile);

    // An else with more sanity checking might be nice here.
  }

  if (i == 3) error_exit("xpidfile %s", name);

  xwrite(fd, spid, sprintf(spid, "%ld\n", (long)getpid()));
  close(fd);
}

// Copy the rest of in to out and close both files.

long long xsendfile(int in, int out)
{
  long long total = 0;
  long len;

  if (in<0) return 0;
  for (;;) {
    len = xread(in, libbuf, sizeof(libbuf));
    if (len<1) break;
    xwrite(out, libbuf, len);
    total += len;
  }

  return total;
}

// parse fractional seconds with optional s/m/h/d suffix
long xparsetime(char *arg, long units, long *fraction)
{
  double d;
  long l;

  if (CFG_TOYBOX_FLOAT) d = strtod(arg, &arg);
  else l = strtoul(arg, &arg, 10);

  // Parse suffix
  if (*arg) {
    int ismhd[]={1,60,3600,86400}, i = stridx("smhd", *arg);

    if (i == -1) error_exit("Unknown suffix '%c'", *arg);
    if (CFG_TOYBOX_FLOAT) d *= ismhd[i];
    else l *= ismhd[i];
  }

  if (CFG_TOYBOX_FLOAT) {
    l = (long)d;
    if (fraction) *fraction = units*(d-l);
  } else if (fraction) *fraction = 0;

  return l;
}

// Compile a regular expression into a regex_t
void xregcomp(regex_t *preg, char *regex, int cflags)
{
  int rc = regcomp(preg, regex, cflags);

  if (rc) {
    regerror(rc, preg, libbuf, sizeof(libbuf));
    error_exit("xregcomp: %s", libbuf);
  }
}

char *xtzset(char *new)
{
  char *old = getenv("TZ");

  if (old) old = xstrdup(old);
  if (new ? setenv("TZ", new, 1) : unsetenv("TZ")) perror_exit("setenv");
  tzset();

  return old;
}

// Set a signal handler
void xsignal(int signal, void *handler)
{
  struct sigaction *sa = (void *)libbuf;

  memset(sa, 0, sizeof(struct sigaction));
  sa->sa_handler = handler;

  if (sigaction(signal, sa, 0)) perror_exit("xsignal %d", signal);
}