busybox源码剖析(2)---pwd.c

 1 extern int pwd_main(int argc, char **argv)
 2 {
 3     static char *buf; 
 4     
 5     buf = xgetcwd(buf);
 6     
 7     if (buf != NULL) {
 8         puts(buf);
 9         return EXIT_SUCCESS;
10     }
11     return EXIT_FAILURE;
12 }

char *
xgetcwd (char *cwd)
{
  char *ret;
  unsigned path_max;
  errno = 0;
  path_max = (unsigned) PATH_MAX;
  path_max += 2;                /* The getcwd docs say to do this. */
  if(cwd==0)
    cwd = xmalloc (path_max);
  errno = 0;
  while ((ret = getcwd (cwd, path_max)) == NULL && errno == ERANGE) {
      path_max += PATH_INCR;
      cwd = xrealloc (cwd, path_max);
      errno = 0;
  }
  if (ret == NULL) {
      int save_errno = errno;
      free (cwd);
      errno = save_errno;
      perror_msg("getcwd()");
      return NULL;
  }
  return cwd;
}