linux 文件复制命令的实现？

#include <config.h>
#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include <assert.h>

#include "system.h"
#include "argmatch.h"
#include "error.h"
#include "fd-reopen.h"
#include "parse-datetime.h"
#include "posixtm.h"
#include "posixver.h"
#include "quote.h"
#include "stat-time.h"
#include "utimens.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "touch"

#define AUTHORS \
  proper_name ("Paul Rubin"), \
  proper_name ("Arnold Robbins"), \
  proper_name ("Jim Kingdon"), \
  proper_name ("David MacKenzie"), \
  proper_name ("Randy Smith")

/* Bitmasks for `change_times'. */
#define CH_ATIME 1
#define CH_MTIME 2

/* Which timestamps to change. */
static int change_times;

/* (-c) If true, don't create if not already there.  */
static bool no_create;

/* (-r) If true, use times from a reference file.  */
static bool use_ref;

/* (-h) If true, change the times of an existing symlink, if possible.  */
static bool no_dereference;

/* If true, the only thing we have to do is change both the
   modification and access time to the current time, so we don't
   have to own the file, just be able to read and write it.
   On some systems, we can do this if we own the file, even though
   we have neither read nor write access to it.  */
static bool amtime_now;

/* New access and modification times to use when setting time.  */
static struct timespec newtime[2];

/* File to use for -r. */
static char *ref_file;

/* For long options that have no equivalent short option, use a
   non-character as a pseudo short option, starting with CHAR_MAX + 1.  */
enum
{
  TIME_OPTION = CHAR_MAX + 1
};

static struct option const longopts[] =
{
  {"time", required_argument, NULL, TIME_OPTION},
  {"no-create", no_argument, NULL, 'c'},
  {"date", required_argument, NULL, 'd'},
  {"reference", required_argument, NULL, 'r'},
  {"no-dereference", no_argument, NULL, 'h'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

/* Valid arguments to the `--time' option. */
static char const* const time_args[] =
{
  "atime", "access", "use", "mtime", "modify", NULL
};

/* The bits in `change_times' that those arguments set. */
static int const time_masks[] =
{
  CH_ATIME, CH_ATIME, CH_ATIME, CH_MTIME, CH_MTIME
};

/* Store into *RESULT the result of interpreting FLEX_DATE as a date,
   relative to NOW.  If NOW is null, use the current time.  */

static void
get_reldate (struct timespec *result,
             char const *flex_date, struct timespec const *now)
{
  if (! parse_datetime (result, flex_date, now))
    error (EXIT_FAILURE, 0, _("invalid date format %s"), quote (flex_date));
}

/* Update the time of file FILE according to the options given.
   Return true if successful.  */

static bool
touch (const char *file)
{
  bool ok;
  int fd = -1;
  int open_errno = 0;
  struct timespec const *t = newtime;

  if (STREQ (file, "-"))
    fd = STDOUT_FILENO;
  else if (! (no_create || no_dereference))
    {
      /* Try to open FILE, creating it if necessary.  */
      int default_permissions =
        S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH;
      fd = fd_reopen (STDIN_FILENO, file,
                      O_WRONLY | O_CREAT | O_NONBLOCK | O_NOCTTY,
                      default_permissions);

      /* Don't save a copy of errno if it's EISDIR, since that would lead
         touch to give a bogus diagnostic for e.g., `touch /' (assuming
         we don't own / or have write access to it).  On Solaris 5.6,
         and probably other systems, it is EINVAL.  On SunOS4, it's EPERM.  */
      if (fd == -1 && errno != EISDIR && errno != EINVAL && errno != EPERM)
        open_errno = errno;
    }

  if (change_times != (CH_ATIME | CH_MTIME))
    {
      /* We're setting only one of the time values.  */
      if (change_times == CH_MTIME)
        newtime[0].tv_nsec = UTIME_OMIT;
      else
        {
          assert (change_times == CH_ATIME);
          newtime[1].tv_nsec = UTIME_OMIT;
        }
    }

  if (amtime_now)
    {
      /* Pass NULL to futimens so it will not fail if we have
         write access to the file, but don't own it.  */
      t = NULL;
    }

  ok = (fdutimensat (fd, AT_FDCWD, (fd == STDOUT_FILENO ? NULL : file), t,
                     (no_dereference && fd == -1) ? AT_SYMLINK_NOFOLLOW : 0)
        == 0);

  if (fd == STDIN_FILENO)
    {
      if (close (STDIN_FILENO) != 0)
        {
          error (0, errno, _("closing %s"), quote (file));
          return false;
        }
    }
  else if (fd == STDOUT_FILENO)
    {
      /* Do not diagnose "touch -c - >&-".  */
      if (!ok && errno == EBADF && no_create)
        return true;
    }

  if (!ok)
    {
      if (open_errno)
        {
          /* The wording of this diagnostic should cover at least two cases:
             - the file does not exist, but the parent directory is unwritable
             - the file exists, but it isn't writable
             I think it's not worth trying to distinguish them.  */
          error (0, open_errno, _("cannot touch %s"), quote (file));
        }
      else
        {
          if (no_create && errno == ENOENT)
            return true;
          error (0, errno, _("setting times of %s"), quote (file));
        }
      return false;
    }

  return true;
}

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
      fputs (_("\
Update the access and modification times of each FILE to the current time.\n\
\n\
A FILE argument that does not exist is created empty, unless -c or -h\n\
is supplied.\n\
\n\
A FILE argument string of - is handled specially and causes touch to\n\
change the times of the file associated with standard output.\n\
\n\
"), stdout);
      fputs (_("\
Mandatory arguments to long options are mandatory for short options too.\n\
"), stdout);
      fputs (_("\
  -a                     change only the access time\n\
  -c, --no-create        do not create any files\n\
  -d, --date=STRING      parse STRING and use it instead of current time\n\
  -f                     (ignored)\n\
"), stdout);
      fputs (_("\
  -h, --no-dereference   affect each symbolic link instead of any referenced\n\
                         file (useful only on systems that can change the\n\
                         timestamps of a symlink)\n\
  -m                     change only the modification time\n\
"), stdout);
      fputs (_("\
  -r, --reference=FILE   use this file's times instead of current time\n\
  -t STAMP               use [[CC]YY]MMDDhhmm[.ss] instead of current time\n\
  --time=WORD            change the specified time:\n\
                           WORD is access, atime, or use: equivalent to -a\n\
                           WORD is modify or mtime: equivalent to -m\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
Note that the -d and -t options accept different time-date formats.\n\
"), stdout);
      emit_ancillary_info ();
    }
  exit (status);
}

int
main (int argc, char **argv)
{
  int c;
  bool date_set = false;
  bool ok = true;
  char const *flex_date = NULL;

  initialize_main (&argc, &argv);
  set_program_name (argv[0]);
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  change_times = 0;
  no_create = use_ref = false;

  while ((c = getopt_long (argc, argv, "acd:fhmr:t:", longopts, NULL)) != -1)
    {
      switch (c)
        {
        case 'a':
          change_times |= CH_ATIME;
          break;

        case 'c':
          no_create = true;
          break;

        case 'd':
          flex_date = optarg;
          break;

        case 'f':
          break;

        case 'h':
          no_dereference = true;
          break;

        case 'm':
          change_times |= CH_MTIME;
          break;

        case 'r':
          use_ref = true;
          ref_file = optarg;
          break;

        case 't':
          if (! posixtime (&newtime[0].tv_sec, optarg,
                           PDS_LEADING_YEAR | PDS_CENTURY | PDS_SECONDS))
            error (EXIT_FAILURE, 0, _("invalid date format %s"),
                   quote (optarg));
          newtime[0].tv_nsec = 0;
          newtime[1] = newtime[0];
          date_set = true;
          break;

        case TIME_OPTION:	/* --time */
          change_times |= XARGMATCH ("--time", optarg,
                                     time_args, time_masks);
          break;

        case_GETOPT_HELP_CHAR;

        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

        default:
          usage (EXIT_FAILURE);
        }
    }

  if (change_times == 0)
    change_times = CH_ATIME | CH_MTIME;

  if (date_set && (use_ref || flex_date))
    {
      error (0, 0, _("cannot specify times from more than one source"));
      usage (EXIT_FAILURE);
    }

  if (use_ref)
    {
      struct stat ref_stats;
      /* Don't use (no_dereference?lstat:stat) (args), since stat
         might be an object-like macro.  */
      if (no_dereference ? lstat (ref_file, &ref_stats)
          : stat (ref_file, &ref_stats))
        error (EXIT_FAILURE, errno,
               _("failed to get attributes of %s"), quote (ref_file));
      newtime[0] = get_stat_atime (&ref_stats);
      newtime[1] = get_stat_mtime (&ref_stats);
      date_set = true;
      if (flex_date)
        {
          if (change_times & CH_ATIME)
            get_reldate (&newtime[0], flex_date, &newtime[0]);
          if (change_times & CH_MTIME)
            get_reldate (&newtime[1], flex_date, &newtime[1]);
        }
    }
  else
    {
      if (flex_date)
        {
          struct timespec now;
          gettime (&now);
          get_reldate (&newtime[0], flex_date, &now);
          newtime[1] = newtime[0];
          date_set = true;

          /* If neither -a nor -m is specified, treat "-d now" as if
             it were absent; this lets "touch" succeed more often in
             the presence of restrictive permissions.  */
          if (change_times == (CH_ATIME | CH_MTIME)
              && newtime[0].tv_sec == now.tv_sec
              && newtime[0].tv_nsec == now.tv_nsec)
            {
              /* Check that it really was "-d now", and not a time
                 stamp that just happens to be the current time.  */
              struct timespec notnow, notnow1;
              notnow.tv_sec = now.tv_sec ^ 1;
              notnow.tv_nsec = now.tv_nsec;
              get_reldate (&notnow1, flex_date, &notnow);
              if (notnow1.tv_sec == notnow.tv_sec
                  && notnow1.tv_nsec == notnow.tv_nsec)
                date_set = false;
            }
        }
    }

  /* The obsolete `MMDDhhmm[YY]' form is valid IFF there are
     two or more non-option arguments.  */
  if (!date_set && 2 <= argc - optind && posix2_version () < 200112
      && posixtime (&newtime[0].tv_sec, argv[optind],
                    PDS_TRAILING_YEAR | PDS_PRE_2000))
    {
      newtime[0].tv_nsec = 0;
      newtime[1] = newtime[0];
      date_set = true;

      if (! getenv ("POSIXLY_CORRECT"))
        {
          struct tm const *tm = localtime (&newtime[0].tv_sec);
          error (0, 0,
                 _("warning: `touch %s' is obsolete; use "
                   "`touch -t %04ld%02d%02d%02d%02d.%02d'"),
                 argv[optind],
                 tm->tm_year + 1900L, tm->tm_mon + 1, tm->tm_mday,
                 tm->tm_hour, tm->tm_min, tm->tm_sec);
        }

      optind++;
    }

  if (!date_set)
    {
      if (change_times == (CH_ATIME | CH_MTIME))
        amtime_now = true;
      else
        newtime[1].tv_nsec = newtime[0].tv_nsec = UTIME_NOW;
    }

  if (optind == argc)
    {
      error (0, 0, _("missing file operand"));
      usage (EXIT_FAILURE);
    }

  for (; optind < argc; ++optind)
    ok &= touch (argv[optind]);

  exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
}