add uversionmangle

[debian/dupmerge.git] / dupmerge.c

/* Dupmerge - Reclaim disk space by linking identical files together

This is a utility that scans a UNIX directory tree looking for pairs of
distinct files with identical content. When it finds such files, it
deletes one file to reclaim its disk space and then recreates its path
name as a link to the other copy.
My first version of this program circa 1993 worked by computing MD5
hashes of every file, sorting the hashes and then looking for duplicates.
This worked, but it was unnecessarily slow. The comparison function I use
now stops comparing two files as soon as it determines their lengths are
different, which is a win when you have many large files with unique lengths.

 * This program reads from standard input a list of files (such
 * as that generated by "find . -print") and discovers which files are
 * identical. Dupmerge unlinks one file of each identical pair and
 * recreates its path name as a link to the other.
 *
 * Non-plain files in the input (directories, pipes, devices, etc)
 * are ignored.  Identical files must be on the same file system to be linked.
 *
 * Dupmerge prefers to keep the older of two identical files, as the older
 * timestamp is more likely to be the correct one given that many
 * copy utilities (e.g., 'cp') do not by default preserve modification
 * times.
 *
 * Dupmerge works by quicksorting a list of path names, with the
 * actual unlinking and relinking steps performed as side effects of
 * the comparison function. The results of the sort are discarded.
 *
 * Command line arguments:
 * -n Suppress the actual unlinking and relinking
 * -q Operate in quiet mode (otherwise, relinks are displayed on stdout)
 *
 * 12 February 1998 Phil Karn, karn@ka9q.ampr.org
 * Copyright Phil Karn. May be used under the terms of the GNU Public License.

--------------------------------------------------------------------------------

Added swap macro, invers mode, no linking of zero length files or files with no disk usage (sparse files),
void casts for semantic checkers, version number, sorting of equal size files due to dev and ino and name,
switched from newline terminated file names to zero terminated file names ...
Switched to C99.
Tested under SuSE 9.2 and Debian (both Kernel 2.6), tested with 4 and 7 Gigabyte files, coreutils sources,
md5 collisions, kernel sources, my archive with CD and DVD collections in an encrypted partition (200 GB, 
1/2 Million files, 5 hours run time, about 30 GB reclaimed by 100,000 hard links).
Changed to reading/writing/comparing 8 byte blocks (instead of 1 byte blocks): 2 times faster now.
Changed inverse mode from O(n*ln(n)) to O(n).
Added sparse and desparse mode and combo flag.
Dr. Rolf Freitag a.k.a. Dr. No, 2004.

For files bigger than 2 GiB, > 2^31 Byte, you should use the compiler option
"-D_FILE_OFFSET_BITS=64".

Example for compilation (and striping + prelinking) on i686 ("PC" with Pentium III or higher or Athlon)
with shell function c (in ~/.bashrc):
function c {
  gcc -Wall -I. -O3 -D_GNU_SOURCE -D__SMP__ -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_REENTRANT \
 -pthread -mcpu=i686 -fexpensive-optimizations -DCPU=686 -ffast-math -m486 -lm -lz -o $1 $1.c && strip $1 \
 && prelink -fmRv ./$1 && chmod +t $1
}

Example usage of this shell function (in ~/.bashrc): c dupmerge

But a simple "gcc -D_GNU_SOURCE -O2 -o dupmerge dupmerge.c" also does the job.

The inverse mode expands the hard links to simple files if used without the option -n.
With option -n hard links are only reported.
The reverse mode can be used e. g. for expanding backups, which have been shrinked with
with the default mode.

Caution: If there is not enough space for expanding the hard links (in inverse mode) hard links
will be lost! It's also a bad idea to kill dupmerge with signal 9 before it finishes because
files can be lost or damaged or new temporary and maybe big files can remain.

example for usage:
find ./ -type f -print0 | dupmerge 2>&1 | tee /tmp/user0/dupmerge.out

Todo:
      - progress meter with approx. percent
      - change from comparing signed to unsigned numbers for clearer ordering
      - inverse mode optimization: expand with the same file attributes (copy most of struct stat)
      - option m <number> for minimum block size; (not file size because of sparse files).
        smaller files will not be hard linked
      - ANSI-C (C99) comppatible error handling of the comparison functions
      - for option n (nodo): normal mode: show the number of blocks which can be saved,
      - refactorisation: separate help function and bit fiels +macros instead of legacy variables
      - error message +advice when wrong parameters are used
      - option f for using a soft link as second try when a hard link could not be made and the reverse for
        inverse mode (inverse mode: expand hard and soft links)
      - option z for not excluding zero length files from linking/expanding/erasing
      - more user friendly output with e. g. freed block + saved space in kB instead of kiB or blocks (see IEC 60027-2),
        extra explanation in output when -n is used,
      - tests with ntfs partitions for MS-Win-users
      - correkt block counting (sparse files are yet not counted correct)
      - man page, info page
      - autoconf/automake + rpm and deb package
      - An option for scheduling in parallel with 2..N pthreads e. g. for SMP boxes with ramdisk.
      - other features like a gziped cvs file with the file attributes from lstat of the files which were
        linked
      - an extra option for creating the tmpfiles on a specified partition for speedup with a ramdisk
      - an option for calling dupmerge with find to shorten the command line the user has to do
      - check if the user has enough permissions to replace files (in not nodo mode)
      - self-calling, "user-friendly", mode with extra option which does calls dupmerge with find via the system call
      - test with files which can be deleted only via the inode (http://www.cyberciti.biz/tips/delete-remove-files-with-inode-number.html)
      - An additional option for doing deletion irreversible via shred or wipe or ... instead of unlink or rm.
        - Checking for and reporting of filesystems where there are no links possible;  e. g. no hard links with FAT.
      - GUI

    Version 1.73, 2008-03-01

 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>             // strndup,
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>             // Nessisary for unlink, gtopt, link, fcmp.
#include <iso646.h>             // for and, bitand, or, bitor ...
#include <stdbool.h>            // _Bool
#include <signal.h>             // signals
#include <limits.h>             // UCHAR_MAX
#include <sys/mman.h>           // mlockall
#include <sys/types.h>          // vfork
#include <sys/wait.h>           // vfork
#include <time.h>               // localtime


#define mc_MIN(a, b) ((a) < (b) ? (a) : (b))
#define mc_MAX(a, b) ((a) > (b) ? (a) : (b))


// Swap two items a, b of size i_size, use (static) swap variable c for performance.
#define mc_SWAP_ITEMS(a, b, c, i_size) { memcpy (&(c), &(a), (i_size));\
                                            memcpy (&(a), &(b), (i_size));\
                                            memcpy (&(b), &(c), (i_size)); }

// easter egg
#define mc_ADVICE if (argc > 1 && 0 == strncmp (argv[1], "-advice", 8) ) \
{ \
  (void)printf ("Don't Panic!\n"); \
  exit (42); \
}                               /* 42: The meaning of life, the universe, and everything ;-) */


// For registering the signal handler void sig_handler (int sig). This macro saves 32 bytes ;-)
#define mc_register_sig_handler \
{\
    int i;\
    for(i=0; i<=UCHAR_MAX; i++)\
      signal (i, sig_handler);\
}


// union for copy and compare
union u_tag
{
  int64_t i64;
  char c[8];
};


int cmp (const void *, const void *);   // function for qsort
int cmp0 (const void *, const void *);  // function for qsort
int fcmp (const void *, const void *);  // function for qsort
int fcmp0 (const void *, const void *); // function for qsort
int fcmp1 (const void *);
int fcmp2 (const void *, const _Bool);
_Bool different_files (const void *, const void *);

const double d_version = 1.73;  // very simple version number of %1.2f format
struct stat s_swap;             // swap variable
int Nodo = 0;                   // for nodo mode (only report)
int Quiet = 0;                  // for quiet mode
int i_soft = 0;                 // for using always soft links instead of the default hard links
_Bool b_inv = false;            // invers mode indicator
_Bool b_sparse = false;         // flag for sparseing
_Bool b_comb = false;           // combo flag for normal + sparse mode
int i_minlinks = 1;             // minimum of found hard links
int i_maxlinks = 1;             // maximum of found hard links
long int li_minblocks = LONG_MAX;       // minimum of saved blocks by sparse copying
long int li_maxblocks = 0;      // maximum of saved blocks by sparse copying
int Files_deleted = 0;
int Blocks_reclaimed = 0;
int i_files_expanded = 0;
int i_blocks_declaimed = 0;
volatile int i_exit_flag = 0;   // flag for exiting soon (not immediately) and controlled after a signal to terminate
char **a_names = NULL;          // array of file names
char *a_flags = NULL;           // Array with the flags of the files in a_names. 1 = marked for deletion because another file the the same content was found,
int nfiles = 0;                 // number of files


void
sig_handler (const int sig)     // signal handler
{
  if ((SIGINT == sig) or (SIGILL == sig) or (SIGKILL == sig) or (SIGSEGV == sig) or (SIGTERM == sig))
  {
    i_exit_flag = 1;            // set the flag for a graceful exit
//    if ((SIGILL == sig) or (SIGKILL == sig) or (SIGSEGV == sig))
//    {
//      (void) printf ("\a\a\a\a\a\a\a Signal %d, program exiting... \r\n\a\a\a", sig);
//      exit (0);
//    }
  }
  return;
}


// initialisation for main
inline void
main_init1 (void)
{
  Files_deleted = 0;
  Blocks_reclaimed = 0;
  i_files_expanded = 0;
  i_blocks_declaimed = 0;
  i_minlinks = 1;
  i_maxlinks = 1;
  li_minblocks = LONG_MAX;
  li_maxblocks = 0;
}


// delete the files (of name a_name[0 ... i_files] which are marked for deletion
void
delete_marked (const int i_files)
{
  struct stat sa;
  int i;

  for (i = 0; i < i_files; i++)
  {
    if (i_exit_flag)
      exit (0);
    if (a_flags[i] bitand 1)    // delete
    {
      if (-1 == lstat (a_names[i], &sa))        // or ! S_ISREG (sa.st_mode))
      {
        fprintf (stderr, "lstat(%s) failed\n", a_names[i]);
        perror ("lstat");
        return;
      }
      if (0 == Nodo)
      {
        printf ("deleting %s, freeing %lld blocks\n", a_names[i], ((1 == sa.st_nlink) ? sa.st_blocks : 0));
        unlink (a_names[i]);
      }
      Files_deleted++;
      if (1 == sa.st_nlink)     // file a is no (hard) link
      {
        Blocks_reclaimed += sa.st_blocks;
      }
    }
  }
  return;
}


int
main (const int argc, const char *const argv[])
{
  char **names, buf[BUFSIZ];    //, *cp;       // BUFSIZE is the default buffer size in stdio.h, usually 8192
  int i, j, i1, i_mode = 0, i_ferror = 0, i_ret = 0;    // integers, mode: 0: common, 1: deletion, i_ferror: for ferror
  FILE *tmp;                    // file pointer for tmpfile
  const char c_zero = '\0';     // for terminating strings
  time_t now;                   // for actual time
  struct tm *ptr_tm = (time (&now), localtime (&now));  // set actual time, convert to localtime

  mc_ADVICE;
  // read parameters for quiet mode and suppressing the actual unlinking and relinking. Rolf Freitag
  while ((i = getopt (argc, (char *const *) argv, "cdhinqsSV")) != EOF)
  {
    switch (i)
    {
      case 'c':
        b_comb = 1;
        break;
      case 'd':
        i_mode = 1;             // deletion mode
        break;
      case 'n':
        Nodo = 1;
        break;
      case 'q':
        Quiet = 1;
        break;
      case 'h':
        fprintf (stdout, "This program can reclaim disk space by linking identical files together.\n");
        fprintf (stdout, "It can also expand all hard links and reads the list of files from standard input.\n");
        fprintf (stdout, "Example usage: find ./ -type f -print0 | dupmerge 2>&1 | tee ../dupmerge_log.txt\n");
        fprintf (stdout, "Options:\n-h \t Show this help and exit.\n-V \t Show version number and exit.\n");
        fprintf (stdout, "-d \t delete multiple files and hard links. Default: Preserve the alphabetically first file name.\n");
        //fprintf (stdout, "   \t Switch for ascessing/decessing order in deletion mode.\n");
        fprintf (stdout, "-q \t Quiet mode.\n-n \t Nodo mode / read-only mode.\n");
        fprintf (stdout, "-i \t Inverse switch: Expand all hard links in normal mode, replace files by their desparsed version if it is bigger.\n");
        fprintf (stdout, "-s \t Flag for soft linking (default is hard linking). This option is beta because for linking of all ");
        fprintf (stdout, "equal files more than one run of dupmerge is necessary and the inverse (expanding of soft links) is untested.\n");
        fprintf (stdout, "-S \t Flag for Sparse mode: Replace files by their sparse version if it is smaller.\n");
        fprintf (stdout, "-c \t Combo mode: Default mode +sparse mode. With -i it means inverse mode with unlinking and desparsing.\n");
        fflush (stdout);
        exit (0);
        break;
      case 's':
        i_soft = 1;
        break;
      case 'V':
        fprintf (stdout, "dupmerge version %1.2f\n", d_version);
        fflush (stdout);
        exit (0);
        break;
      case 'i':
        b_inv = true;
        break;
      case 'S':
        b_sparse = true;
        break;
      default:
        break;
    }
  }
  if (not Quiet)
  {
    (void) printf ("%s started at %d-%s%d-%s%d %s%d:%s%d:%s%d\n", argv[0],
                   ptr_tm->tm_year + 1900, ptr_tm->tm_mon + 1 > 9 ? "" : "0", ptr_tm->tm_mon + 1,
                   ptr_tm->tm_mday > 9 ? "" : "0", ptr_tm->tm_mday,
                   ptr_tm->tm_hour > 9 ? "" : "0", ptr_tm->tm_hour,
                   ptr_tm->tm_min > 9 ? "" : "0", ptr_tm->tm_min, ptr_tm->tm_sec > 9 ? "" : "0", ptr_tm->tm_sec);
    fflush (stdout);
  }
#ifndef __CYGWIN__
  mlockall (MCL_CURRENT bitor MCL_FUTURE);      // be cached
#endif
  // Read list of file names into tmp file and count
  tmp = tmpfile ();
  if (NULL == tmp)
  {
    (void) fprintf (stderr, "could not open temporary file, exiting\n");
    exit (-1);
  }
  nfiles = 0;
  if (not Quiet)
  {
    (void) printf ("tmpfile (pointer %p) created, processing ...\n", tmp);
    fflush (stdout);
  }
  while (!feof (stdin))         // while not end of input
  {
    buf[0] = '\0';              // set strnlen to 0 so that strnlen (buf, BUFSIZ) is 0 at EOF
    for (i = 0; i < BUFSIZ; i++)        // read till the sequence operator \0 is found
    {
      fread (&buf[i], 1, 1, stdin);
      i_ferror = ferror (stdin);
      if (i_ferror)
      {
        (void) fprintf (stderr, "stdin: error %d.\n", i_ferror);
        i_ret = -1;
      }
      if ('\0' == buf[i])       // termination found
        break;
    }
    if ('\0' not_eq buf[sizeof (buf) - 1])      // no termination at buffer end
      buf[sizeof (buf) - 1] = '\0';
    if (strnlen (buf, BUFSIZ))
      nfiles++;                 // new file: increment file counter
    if ((EOF == fputs (buf, tmp)) or (not fwrite (&c_zero, 1, 1, tmp))) // store new file name in tmp file
    {
      (void) fprintf (stderr, "could not write to temporary file, exiting\n");
      exit (-1);
    }
  }
  // Now that we know how many there are, printf, allocate space and re-read.
  if (not Quiet)
  {
    (void) printf ("Input: %d files, processing ...\n", nfiles);
    fflush (stdout);
  }
  if (0 == nfiles)              // no input, nothing to do
    exit (0);
  rewind (tmp);
  names = (char **) calloc (nfiles, sizeof (char *));
  a_names = (char **) calloc (nfiles, sizeof (char *));
  a_flags = (char *) calloc (nfiles, sizeof (char));
  if ((NULL == names) or (NULL == a_flags) or (NULL == a_names))
  {
    (void) fprintf (stderr, "%s: Out of memory\n", argv[0]);
    exit (-1);
  }
  for (i = 0; i < nfiles; i++)  // get the file names from the tmp file
  {
    for (j = 0; j < BUFSIZ; j++)        // read till the sequence operator \0 is found
    {
      fread (&buf[j], 1, 1, tmp);
      i_ferror = ferror (stdin);
      if (i_ferror)
      {
        (void) fprintf (stderr, "tmpfile: error %d.\n", i_ferror);
        i_ret = -1;
      }
      if ('\0' == buf[j])       // termination found
        break;
    }
    if ((NULL == (names[i] = strndup (buf, BUFSIZ))) or (NULL == (a_names[i] = strndup (buf, BUFSIZ))))
    {                           // The command "gcc -o dupmerge dupmerge.c" prduces the Warning "dupmerge.c:191: warning: assignment
      // makes pointer from integer without a cast" but this is a warning bug; in the if statement above there is no int!
      // To get rid of that warning you can cast strndup to (char *) or equivalent (typeof(names[i])) or use -O3. [gcc version 3.3.4]
      // For later versions of gcc you should use the command line option -D_GNU_SOURCE, but that's not necessary under cygwin.
      (void) fprintf (stderr, "%s: Out of memory\n", argv[0]);
      exit (1);
    }
  }
  (void) fclose (tmp);
  mc_register_sig_handler;      // register signal handler before critical sections
  qsort (a_names, nfiles, sizeof (char *), cmp0);       // sort only the (pointers to the) file names in a_names
  switch (i_mode)
  {
    case 0:                    // no deletion
      switch (b_comb and b_inv) // For desparse mode after nomal inverted mode. Otherwise a second run would be nessisary.
      {
        case 0:                // not combo mode and inverse switch
          if (b_sparse)         // sparse/desparse files first because sparsing/desparsing expands hard links (changes inode)
          {
            // no sorted list of files at this point
            i1 = Quiet;
            if (b_comb and Nodo)        // combo mode and read-only (Nodo): do nodo sparsing/desparsing during sorting with output here
              Quiet = 0;
            else
              Quiet = 1;
            i = Nodo;
            Nodo = 1;           // for only sorting the names
            qsort (names, nfiles, sizeof (char *), fcmp);       // sort only the (pointers to the) file names
            Nodo = i;           // restore Nodo
            Quiet = i1;         // restore Quiet
          foo:
            main_init1 ();      // start with new init
            // sparse or desparse
            for (i = 0; i < nfiles; i++)
            {
              // only different files, call fcmp2/3 only for the last file in a block of equal hard links
              if ((nfiles - 1 == i) or different_files (names + i, names + i + 1))
                (void) fcmp2 (names + i, not b_inv);
            }
            if (not Quiet)
            {
              (void)
                printf
                ("Files%s %ssparsed: %d of %d, Disk blocks%s %sclaimed: %d\n",
                 (Nodo ? " which can be" : ""), (b_inv ? "de" : ""),
                 (b_inv ? i_files_expanded : Files_deleted), nfiles,
                 (Nodo ? " can be" : ""), (b_inv ? "de" : "re"), (b_inv ? i_blocks_declaimed : Blocks_reclaimed));
              (void)
                printf
                ("Minimum of disk blocks which could be %s by %s copying: %ld, Maximum: %ld.\n",
                 (b_inv ? "declaimed" : "reclaimed"), (b_inv ? "desparse" : "sparse"), li_minblocks, li_maxblocks);
              fflush (stdout);
            }
            if ((b_comb and Nodo) or (b_inv))   // all work done
              exit (0);
          }                     // if (b_sparse), no break
        case 1:
          main_init1 ();        // start with new init
          if ((b_sparse and b_comb) or (not b_sparse))  // sparse mode +combo flag or no sparse mode: normal mode, maybe with inversion
          {                     // Without the combo flag and with sparse mode there is no normal (maybe inverted) mode!
            if (not b_inv)
            {
              qsort (names, nfiles, sizeof (char *), fcmp);
              if (not Quiet)
              {
                (void) printf ("Scanning for more dups ...\n");
                fflush (stdout);
              }
              for (i = 0; i <= nfiles - 2; i++) // Second run: nessisary for qsort versions which do use cached values, where fcmp is not always called,
                (void) fcmp (names + i, names + i + 1); // e. g. with gcc qsort at coreutil sources.
            }
            else
            {
              if (not Quiet)
              {
                (void) printf ("Scanning for hard links ...\n");
                fflush (stdout);
              }
              for (i = 0; i < nfiles; i++)
                (void) fcmp1 (names + i);
            }
            if (not Quiet)
            {
              (void)
                printf
                ("Files%s %s: %d of %d, Disk blocks%s %sclaimed: %d\n",
                 (Nodo ? " which can be" : ""),
                 (b_inv ? "expanded" : "linked"),
                 (b_inv ? i_files_expanded : Files_deleted), nfiles,
                 (Nodo ? " which can be" : ""), (b_inv ? "de" : "re"), (b_inv ? i_blocks_declaimed : Blocks_reclaimed));
              (void) printf ("Minimum of found hard links: %d, Maximum: %d.\n", i_minlinks, i_maxlinks);
              fflush (stdout);
            }
          }                     // if ((b_sparse and b_comb) or (not b_sparse))
          if (b_comb and b_inv) // do desparsing in inverse mode
            goto foo;
          break;
        default:
          (void) printf ("Unexpected switch error ...\n");
          exit (-1);
          break;
      }                         // switch
      break;
    case 1:                    // deletion
      // no sorted list of files at this point
      qsort (names, nfiles, sizeof (char *), fcmp0);    // sort only the file names
      // second run
      for (i = 0; i <= nfiles - 2; i++) // Second run: nessisary for qsort versions which do use cached values, where fcmp is not always called,
        (void) fcmp0 (names + i, names + i + 1);        // e. g. with gcc qsort at coreutil sources.
      delete_marked (nfiles);
      if (not Quiet)
      {
        (void)
          printf
          ("Duplicate files (%s deleted): %d of %d, Disk blocks%s reclaimed: %d\n",
           (Nodo ? "which can be" : "which have been"), (b_inv ? i_files_expanded : Files_deleted), nfiles, (Nodo ? " which can be" : ""), Blocks_reclaimed);
        (void) printf ("Minimum of found hard links: %d, Maximum: %d.\n", i_minlinks, i_maxlinks);
        fflush (stdout);
      }
      break;
    default:
      (void) printf ("Unexpected switch error ...\n");
      exit (-1);
      break;
  }                             // switch
  exit (i_ret);
}                               // main


// For alphabetic ordering/searching.
int
cmp (const void *p0, const void *p1)
{
  int i = 0;
  char **p2 = (char **) p0;
  char **p3 = (char **) p1;
  i = strncmp (*p2, *p3, BUFSIZ);       // compare the two strings
  return (i);
}


// For alphabetic ordering/searching. With global inversion flag for inverse mode.
int
cmp0 (const void *p0, const void *p1)
{
  int i = 0;
  char **p2 = (char **) p0;
  char **p3 = (char **) p1;
  i = strncmp (*p2, *p3, BUFSIZ);       // compare the two strings
  if (b_inv)
    return (-i);
  return (i);
}


// This is the comparison function called by qsort, where the real work
// is done as a side effect. Due to ANSI-C the current version is not
// completely correct because if the same objects are passed more than once to the
// comparison function the results must be consistent with another; see 7.20.5  in C99.
// If errors like lstat failed do occur, this is not fullfilled yet. With fcmp1 it's the same.
// sort levels: 0: size (and accessability), 1: device, 2: content, 3.: name
int
fcmp (const void *a, const void *b)
{
  struct stat sa, sb;
  FILE *fa, *fb;
  int i1, i2, i_nlinka, i_nlinkb, i_fa, i_fb;
  int rval = 0;
  const char *filea, *fileb;
  union u_tag u_buffer1 = {
    0
  }, u_buffer2 =
  {
  0};
  void *buffer1 = (void *) &u_buffer1;
  void *buffer2 = (void *) &u_buffer2;
  _Bool b_swap = false;

  if (i_exit_flag)
    exit (0);
  // Nonexistent or non-plain files are less than any other file
  if (NULL == a)
    return (-1);
  filea = *(const char **) a;
  if (-1 == lstat (filea, &sa)) // or ! S_ISREG (sa.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", filea);
    perror ("lstat");
    return (-1);
  }
  if (NULL == b)
    return 1;
  fileb = *(const char **) b;
  if (-1 == lstat (fileb, &sb)) // or ! S_ISREG (sb.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", fileb);
    perror ("lstat");
    return (1);
  }
  i_minlinks = mc_MIN (i_minlinks, mc_MIN (sa.st_nlink, sb.st_nlink));
  i_maxlinks = mc_MAX (i_maxlinks, mc_MAX (sa.st_nlink, sb.st_nlink));
  // Smaller files are "less"
  if (sa.st_size < sb.st_size)
    return (-1);
  if (sa.st_size > sb.st_size)
    return (1);
  // We now know both files exist, are plain files, are the same size
  // if both files are hard linked or zero length: sort by name
  if (((sa.st_dev == sb.st_dev) and (sa.st_ino == sb.st_ino)) or (0 == sa.st_size))
    return (strncmp (filea, fileb, BUFSIZ));
  // We now know both files exist, are plain files, are the same size > 0,
  // and are not already linked, so compare them alphabetical, if they are on the same device
  if (sa.st_dev != sb.st_dev)
    return ((sa.st_dev < sb.st_dev) ? -1 : 1);
  if (NULL == (fa = fopen (filea, "r")))
    return (-1);                // Unreadable files are "less than"
  if (NULL == (fb = fopen (fileb, "r")))
  {
    fclose (fa);
    return (1);
  }
  // Loop for comparing the files in 64 bit (instead of 8 bit) blocks.
  // On big endian machines it's alphabetic ordering, on little andian machines it's
  // alphabetic ordering with 64 bit 'characters'.
  // Du to C99, 7.19.8.1 read must be done with chars.
  while (((i1 = fread (buffer1, 1, 8, fa)) != 0) and ((i2 = fread (buffer2, 1, 8, fb)) != 0))
  {
    // Mask the unsused 1..7 bytes, because the standard says nothing about them.
    memset (&(u_buffer1.c[i1]), 0, 8 - i1);     // start at the first unused byte buffer1.c[i1], end at Byte7 buffer1.c[7]
    memset (&(u_buffer2.c[i2]), 0, 8 - i2);
    // check for file errors
    i_fa = ferror (fa);
    i_fb = ferror (fb);
    if (i_fa or i_fb)           // check for file errors
    {
      if (i_fa)
      {
        (void) fprintf (stderr, "file %s: error %d.\n", filea, i_fa);
        rval = -1;              // error file: smaller
        break;
      }
      if (i_fb)
      {
        (void) fprintf (stderr, "file %s: error %d.\n", fileb, i_fb);
        rval = 1;
        break;
      }
    }
    if (u_buffer1.i64 != u_buffer2.i64) // compare
    {
      rval = (u_buffer1.i64 < u_buffer2.i64) ? -1 : 1;
      break;
    }
  }
  (void) fclose (fa);
  (void) fclose (fb);
  if (rval)                     // unequal files of same size
    return rval;

  if ((sa.st_blocks) or (sb.st_blocks)) // avoid linking sparse files with no blocks allocated
  {
    // The two files have same content, size > 0, blocks allocated > 0 and are on the same device, so link them.
    // We prefer to keep the one with less blocks, or if they're the
    // same the older one, or if they're the same, the one with more (hard) links.
    if ((sb.st_blocks < sa.st_blocks) or (sb.st_mtime > sa.st_mtime) or (sb.st_nlink < sa.st_nlink))
    {
      mc_SWAP_ITEMS (sa, sb, s_swap, sizeof (struct stat));     // swap items to keep original sb
      mc_SWAP_ITEMS (filea, fileb, s_swap, sizeof (char *));    // swap file name pointers
      b_swap = true;
    }
    // before linking: store number of hard links of each file
    i_nlinka = sa.st_nlink;
    i_nlinkb = sb.st_nlink;
    if (1 == sa.st_nlink)       // file a is no (hard) link
    {
      Files_deleted++;
      Blocks_reclaimed += sa.st_blocks;
    }
    if (!Nodo and (unlink (filea)))
    {
      (void) fprintf (stderr, "unlink(%s) failed\n", filea);
      perror ("unlink");
      return (-1);
    }
    if (!i_soft)
    {
      if (!Nodo and (-1 == link (fileb, filea)))
      {
        (void) fprintf (stderr, "link(%s,%s) failed\n", fileb, filea);
        perror ("link");
        return (-1);
      }
    }
    else
    {
      if (!Nodo and (-1 == symlink (fileb, filea)))
      {
        (void) fprintf (stderr, "symlink(%s,%s) failed\n", filea, fileb);
        perror ("symlink");
        return (-1);
      }
    }
    if (!Quiet)
    {
      (void) printf ("ln %s %s %s: %d, %d -> %d, freed +%llu blocks\n", i_soft ? "-s" : "", fileb, filea, i_nlinkb, i_nlinka, i_nlinka + i_nlinkb,
                     sb.st_blocks);
      fflush (stdout);
    }
  }
  return ((b_swap) ? strncmp (fileb, filea, BUFSIZ) : strncmp (filea, fileb, BUFSIZ));  //
}                               // fcmp


// return the index of file with name a_name
int
nindex (const char *a_name)
{
  void *p_v = bsearch (&a_name, a_names, nfiles, sizeof (char *), cmp0);
  int i_ret = (int) (((((void *) p_v) - ((void *) a_names))) / (sizeof (char *)));
  if (NULL == p_v)
  {
    printf ("Error: bsearch(%s, %p, %d, %d, %p) returned NULL.\n", a_name, a_names, nfiles, sizeof (char *), cmp);
    return (-1);                // error
  }
  return (i_ret);
}


// This is the comparison function called by qsort, for marking all duplicate files with that flag
// Due to ANSI-C the current version is not
// completely correct because if the same objects are passed more than one to the
// comparison function the results must be consistent with another, 7.20.5 C99.
// If errors like lstat failed do occur, this is not fullfilled yet.
// sort levels: 0: size (and accessability), 1: device, 2: content, 3.: name
int
fcmp0 (const void *a, const void *b)
{
  struct stat sa, sb;
  FILE *fa, *fb;
  int i1, i2;
  int rval = 0, ja = 0, jb = 0, i_fa, i_fb;
  const char *filea, *fileb;
  union u_tag u_buffer1 = {
    0
  }, u_buffer2 =
  {
  0};
  void *buffer1 = (void *) &u_buffer1;
  void *buffer2 = (void *) &u_buffer2;

  if (i_exit_flag)
    exit (0);
  // Nonexistent or non-plain files are less than any other file
  if (NULL == a)
    return (-1);
  filea = *(const char **) a;
  if (-1 == lstat (filea, &sa)) // or ! S_ISREG (sa.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", filea);
    perror ("lstat");
    return (-1);
  }
  if (NULL == b)
    return 1;
  fileb = *(const char **) b;
  if (-1 == lstat (fileb, &sb)) // or ! S_ISREG (sb.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", fileb);
    perror ("lstat");
    return (1);
  }
  i_minlinks = mc_MIN (i_minlinks, mc_MIN (sa.st_nlink, sb.st_nlink));
  i_maxlinks = mc_MAX (i_maxlinks, mc_MAX (sa.st_nlink, sb.st_nlink));
  // Smaller files are "less"
  if (sa.st_size < sb.st_size)
    return (-1);
  if (sa.st_size > sb.st_size)
    return (1);
  // We now know both files exist, are plain files, are the same size
  // if both files are hard linked: sort by name
  if (((sa.st_dev == sb.st_dev) and (sa.st_ino == sb.st_ino)))
  {
  out_equal:
    // set ja, jb to the index of a, b
    ja = nindex (filea);
    jb = nindex (fileb);
    if ((ja >= 0) and (a_flags[ja] bitand 1))
      return (-1);              // marked file first
    if ((jb >= 0) and (a_flags[jb] bitand 1))
      return (1);               // marked file first
    // now both files are not marked
    if ((ja >= 0) and (jb >= 0))
    {
      if ((b_inv ? -1 : 1) * strncmp (filea, fileb, BUFSIZ) <= 0)       // alphabetic ordering
      {
        a_flags[ja] = 1;
        if (!Quiet)
        {
          (void) printf ("Equal files: %s will get deleted, %s will get preserved.\n", filea, fileb);
          fflush (stdout);
        }
        return (-1);            // marked file first
      }
      else
      {
        a_flags[jb] = 1;
        if (!Quiet)
        {
          (void) printf ("Equal files: %s will get deleted, %s will get preserved.\n", fileb, filea);
          fflush (stdout);
        }
        return (1);             // marked file first
      }
    }
    return ((b_inv ? -1 : 1) * strncmp (filea, fileb, BUFSIZ));
  }
  // We now know both files exist, are plain files, are the same size > 0,
  // and are not already linked, so compare them alphabetical
  if (NULL == (fa = fopen (filea, "r")))
    return (-1);                // Unreadable files are "less than"
  if (NULL == (fb = fopen (fileb, "r")))
  {
    fclose (fa);
    return 1;
  }
  // Loop for comparing the files in 64 bit (instead of 8 bit) blocks.
  // On big endian machines it's alphabetic ordering, on little andian machines it's
  // alphabetic ordering with 64 bit 'characters'.
  while (((i1 = fread (buffer1, 1, 8, fa)) != 0) and ((i2 = fread (buffer2, 1, 8, fb)) != 0))
  {
    // Mask the unsused 1..7 bytes, because the standard says nothing about them.
    memset (&(u_buffer1.c[i1]), 0, 8 - i1);     // start at the first unused byte buffer1.c[i1], end at Byte7 buffer1.c[7]
    memset (&(u_buffer2.c[i2]), 0, 8 - i2);
    // check for file errors
    i_fa = ferror (fa);
    i_fb = ferror (fb);
    if (i_fa or i_fb)           // check for file errors
    {
      if (i_fa)
      {
        (void) fprintf (stderr, "file %s: error %d.\n", filea, i_fa);
        rval = -1;              // error file: smaller
        break;
      }
      if (i_fb)
      {
        (void) fprintf (stderr, "file %s: error %d.\n", fileb, i_fb);
        rval = 1;
        break;
      }
    }
    if (u_buffer1.i64 != u_buffer2.i64) // compare
    {
      rval = (u_buffer1.i64 < u_buffer2.i64) ? -1 : 1;
      break;
    }
  }
  (void) fclose (fa);
  (void) fclose (fb);
  if (rval)                     // unequal files of same size
    return rval;
  // else
  goto out_equal;
}                               // fcmp0


// This is the hard link expansion function for the inverse mode. Needs only one file name as argument.
int
fcmp1 (const void *a)
{
  struct stat sa;
  FILE *fa, *fb;
  int i1, i, i_b, i_fa, i_fb, i_ret = 0;
  char a_cd[BUFSIZ] = { '\0' }; // for directory
  char a_cf[BUFSIZ] = { '\0' }; // for tempfile
  const char *filea, *fileb = a_cf;     // file names, fileb after mkstemp
  union u_tag u_buffer1 = {
    0
  };
  void *buffer1 = (void *) &u_buffer1;

  if (i_exit_flag)
    exit (0);
  // Nonexistent or non-plain files are less than any other file
  if (NULL == a)
    return (-1);
  filea = *(const char **) a;
  if (-1 == lstat (filea, &sa)) // or ! S_ISREG (sa.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", filea);
    perror ("lstat");
    return (-1);
  }
  i_minlinks = mc_MIN (i_minlinks, sa.st_nlink);
  i_maxlinks = mc_MAX (i_maxlinks, sa.st_nlink);
  // check for hard links
  if (sa.st_nlink > 1)          // hard link found
  {
    i_files_expanded++;
    i_blocks_declaimed += sa.st_blocks;
    if (!Nodo)                  // expand the hard link
    {
      strncpy (a_cd, filea, BUFSIZ);
      // extract the directory from the file name: delete from end to last "/"
      for (i = strnlen (a_cd, BUFSIZ); i >= 0; i--)
      {
        if (a_cd[i] != '/')
          a_cd[i] = '\0';
        else
          break;
      }
      // now the actual directory is in a_c, create temporary file there
      strncpy (a_cf, a_cd, BUFSIZ);
      strncat (a_cf, "dup__XXXXXXX", BUFSIZ / 2);       // template for mkstemp
      i_b = mkstemp (a_cf);
      if (-1 == i_b)
      {
        (void) fprintf (stderr, "Could not create temporary file.\n");
        perror ("file_create");
        return (-1);
      }
      if ((NULL == (fa = fopen (filea, "r"))) or (NULL == (fb = fdopen (i_b, "w"))))    // open file and tmpfile
      {
        (void) fprintf (stderr, "Expanding the hard link(%s) failed.\n", filea);
        perror ("expand");
        return (-1);
      }
      // expand to tmpfile
      while ((i1 = fread (buffer1, 1, 8, fa)) != 0)     // copy fa to fb in 8 byte blocks
      {
        (void) fwrite (buffer1, 1, i1, fb);
      }
      i_fa = ferror (fa);
      i_fb = ferror (fb);
      if (i_fa or i_fb)         // check for file errors
      {
        if (i_fa)
          (void) fprintf (stderr, "file %s: error %d.\n", filea, i_fa);
        if (i_fb)
          (void) fprintf (stderr, "file %s: error %d.\n", fileb, i_fb);
        i_ret = -1;
      }
      (void) fclose (fa);
      (void) fclose (fb);
      // unlink
      if (unlink (filea))
      {
        (void) fprintf (stderr, "unlink(%s) failed, tempfile %s remains\n", filea, fileb);
        perror ("unlink");
        return (-1);
      }
      // rename to original name
      if (rename (fileb, filea))
      {
        (void) fprintf (stderr, "rename(%s, %s) failed, tempfile %s remains\n", fileb, filea, fileb);
        perror ("unlink");
        return (-1);
      }
    }                           // if (!Nodo)
    if (!Quiet)
    {
      (void) printf ("expand %s: %d -> %d, unfreed %llu blocks\n", filea, sa.st_nlink, sa.st_nlink - 1, sa.st_blocks);  // sa has the old cached value
      fflush (stdout);
    }
  }                             // if (sa.st_ino > 1)
  return (i_ret);
}                               // fcmp1


// This is the (de)sparsing function.
// Copying sparse/desparse can reduce/increase st_blocks while st_size remains constant.
int
fcmp2 (const void *a, const _Bool b_S)
{
  FILE *fb;
  struct stat sa, sb;
  int i, i_b, status = 0, i_pid, i_ret = 0;
  long int li;
  char a_cd[BUFSIZ] = { '\0' }; // for directory, temporary string
  char a_cf[BUFSIZ] = { '\0' }; // for tempfile
  char a_ca[BUFSIZ] = { '\0' }; // for tempfile
  const char *filea = a_ca, *fileb = a_cf;      // file names

  if (i_exit_flag)
    exit (0);
  // Nonexistent or non-plain files are less than any other file
  if (NULL == a)
    return (-1);
  strncpy (a_ca, *(const char **) a, BUFSIZ - 1);
  // filea = *(const char **) a;
  if (-1 == lstat (filea, &sa)) // or ! S_ISREG (sa.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", filea);
    perror ("lstat");
    return (-1);
  }
  // get tmpname: mkstemp, unlink
  strncpy (a_cd, filea, BUFSIZ);
  // extract the directory from the file name: delete from end to last "/"
  for (i = strnlen (a_cd, BUFSIZ); i >= 0; i--)
  {
    if (a_cd[i] != '/')
      a_cd[i] = '\0';
    else
      break;
  }
  // now the actual directory is in a_c, create temporary file there
  strncpy (a_cf, a_cd, BUFSIZ);
  strncat (a_cf, "dup__XXXXXXX", BUFSIZ / 2);   // template for mkstemp
  i_b = mkstemp (a_cf);
  if (-1 == i_b)
  {
    (void) fprintf (stderr, "Could not create temporary file.\n");
    perror ("mkstemp");
    return (-1);
  }
  // dummy open and close to close the tmpfile
  if (NULL == (fb = fdopen (i_b, "w"))) // open tmpfile
  {
    (void) fprintf (stderr, "fdopen (%d) failed.\n", i_b);
    perror ("fdopen");
    return (-1);
  }
  fclose (fb);
  if (unlink (fileb))           // delete file because we do need only the name
  {
    (void) fprintf (stderr, "unlink(%s) failed\n", fileb);
    perror ("unlink");
    return (-1);
  }
  switch (i_pid = vfork ())
  {
    case -1:                   // parent with fork error
      perror ("vfork");
      fprintf (stderr, "vfork failed.\n");
      break;
    case 0:                    // child
      memset (a_cd, '\0', sizeof (a_cd));
      strncpy (a_cd, (b_S ? "--sparse=always" : "--sparse=never"), BUFSIZ);
      i = execl ("/bin/cp", "cp", a_cd, filea, fileb, NULL);
      if (i)
      {
        fprintf (stderr, "execlp(cp %s %s %s) failed, return value %d\n", a_cd, filea, fileb, i);
        perror ("fork");
      }
      _exit (i);
      break;
    default:                   // parent with no error: do proceed
      break;
  }
  i = waitpid (i_pid, &status, WUNTRACED);      // wait till child terminates
  if (status)
  {
    fprintf (stderr, "copying failed; child with pid %d returned %d\n", i, status);
    i_ret = -1;
    goto end;
  }
  // lstat and check copy
  if (-1 == lstat (fileb, &sb)) // or ! S_ISREG (sb.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", fileb);
    perror ("lstat");
    return (-1);
  }
  li = sa.st_blocks - sb.st_blocks;
  if (not b_S)
    li = -li;
  li_minblocks = mc_MIN (li_minblocks, li);
  li_maxblocks = mc_MAX (li_maxblocks, li);
  // if shrinked in sparse mode or expanded in desparse mode: unlink original and rename tmpfile to original name
  if ((b_S ? (sa.st_blocks > sb.st_blocks) : (sa.st_blocks < sb.st_blocks)))
  {
    b_S ? Files_deleted++ : i_files_expanded++;
    b_S ? (Blocks_reclaimed += sa.st_blocks - sb.st_blocks) : (i_blocks_declaimed += sb.st_blocks - sa.st_blocks);
    if (!Quiet)
    {
      (void) printf ("%s: %lld -> %lld blocks\n", filea, sa.st_blocks, sb.st_blocks);
      fflush (stdout);
    }
    if (not Nodo)
    {
      if (unlink (filea))       // delete original
      {
        (void) fprintf (stderr, "unlink(%s) failed\n", filea);
        perror ("unlink");
        return (-1);
      }
      // rename to original name
      if (rename (fileb, filea))
      {
        (void) fprintf (stderr, "rename(%s, %s) failed\n", fileb, filea);
        perror ("unlink");
        i_ret = -1;
        goto end;
      }
      return (0);
    }
  }
end:
  if (unlink (fileb))           // delete tmpfile
  {
    (void) fprintf (stderr, "unlink(%s) failed\n", fileb);
    perror ("unlink");
    return (-1);
  }
  return (i_ret);
}                               // fcmp2


// return true if the two files are not hard linkded
_Bool
different_files (const void *a, const void *b)
{
  struct stat sa, sb;
  const char *filea, *fileb;

  // Nonexistent or non-plain files are less than any other file
  if (NULL == a)
    return (true);
  filea = *(const char **) a;
  if (-1 == lstat (filea, &sa)) // or ! S_ISREG (sa.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", filea);
    perror ("lstat");
    return (true);
  }
  if (NULL == b)
    return (true);
  fileb = *(const char **) b;
  if (-1 == lstat (fileb, &sb)) // or ! S_ISREG (sb.st_mode))
  {
    fprintf (stderr, "lstat(%s) failed\n", fileb);
    perror ("lstat");
    return (true);
  }
  if ((sa.st_dev == sb.st_dev) and (sa.st_ino == sb.st_ino))    // same device and same inode?
    return (false);             // yes: equal files
  return (true);
}                               // different_files