link-by-hash.diff

   1 Jason M. Felice wrote:
   2
   3 This patch adds the --link-by-hash=DIR option, which hard links received
   4 files in a link farm arranged by MD4 file hash.  The result is that the system
   5 will only store one copy of the unique contents of each file, regardless of
   6 the file's name.
   7
   8 To use this patch, run these commands for a successful build:
   9
  10     patch -p1 <patches/link-by-hash.diff
  11     ./prepare-source
  12     ./configure
  13     make
  14
  15 based-on: 24079e988fc31af4eba56cd2701fdc5a4154980d
  16 diff --git a/Makefile.in b/Makefile.in
  17 --- a/Makefile.in
  18 +++ b/Makefile.in
  19 @@ -37,7 +37,7 @@ OBJS1=flist.o rsync.o generator.o receiver.o cleanup.o sender.o exclude.o \
  20         util.o main.o checksum.o match.o syscall.o log.o backup.o delete.o
  21  OBJS2=options.o io.o compat.o hlink.o token.o uidlist.o socket.o hashtable.o \
  22         fileio.o batch.o clientname.o chmod.o acls.o xattrs.o
  23 -OBJS3=progress.o pipe.o
  24 +OBJS3=progress.o pipe.o hashlink.o
  25  DAEMON_OBJ = params.o loadparm.o clientserver.o access.o connection.o authenticate.o
  26  popt_OBJS=popt/findme.o  popt/popt.o  popt/poptconfig.o \
  27         popt/popthelp.o popt/poptparse.o
  28 diff --git a/flist.c b/flist.c
  29 --- a/flist.c
  30 +++ b/flist.c
  31 @@ -72,6 +72,7 @@ extern int sender_keeps_checksum;
  32  extern int unsort_ndx;
  33  extern struct stats stats;
  34  extern char *filesfrom_host;
  35 +extern char *link_by_hash_dir;
  36  extern char *usermap, *groupmap;
  37
  38  extern char curr_dir[MAXPATHLEN];
  39 @@ -908,7 +909,7 @@ static struct file_struct *recv_file_entry(int f, struct file_list *flist, int x
  40                 extra_len += EXTRA_LEN;
  41  #endif
  42
  43 -       if (always_checksum && S_ISREG(mode))
  44 +       if ((always_checksum || link_by_hash_dir) && S_ISREG(mode))
  45                 extra_len += SUM_EXTRA_CNT * EXTRA_LEN;
  46
  47  #if SIZEOF_INT64 >= 8
  48 diff --git a/hashlink.c b/hashlink.c
  49 new file mode 100644
  50 --- /dev/null
  51 +++ b/hashlink.c
  52 @@ -0,0 +1,339 @@
  53 +/*
  54 +   Copyright (C) Cronosys, LLC 2004
  55 +
  56 +   This program is free software; you can redistribute it and/or modify
  57 +   it under the terms of the GNU General Public License as published by
  58 +   the Free Software Foundation; either version 2 of the License, or
  59 +   (at your option) any later version.
  60 +
  61 +   This program is distributed in the hope that it will be useful,
  62 +   but WITHOUT ANY WARRANTY; without even the implied warranty of
  63 +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  64 +   GNU General Public License for more details.
  65 +
  66 +   You should have received a copy of the GNU General Public License
  67 +   along with this program; if not, write to the Free Software
  68 +   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  69 +*/
  70 +
  71 +/* This file contains code used by the --link-by-hash option. */
  72 +
  73 +#include "rsync.h"
  74 +
  75 +extern char *link_by_hash_dir;
  76 +
  77 +#ifdef HAVE_LINK
  78 +
  79 +char *make_hash_name(struct file_struct *file)
  80 +{
  81 +       char hash[33], *dst;
  82 +       uchar c, *src = (uchar*)F_SUM(file);
  83 +       int i;
  84 +
  85 +       for (dst = hash, i = 0; i < 4; i++, src++) {
  86 +               c = *src >> 4;
  87 +               *(dst++) = (c >= 10) ? (c - 10 + 'a') : (c + '0');
  88 +               c = *src & 0x0f;
  89 +               *(dst++) = (c >= 10) ? (c - 10 + 'a') : (c + '0');
  90 +       }
  91 +       *dst++ = '/';
  92 +       for (i = 0; i < 12; i++, src++) {
  93 +               c = *src >> 4;
  94 +               *(dst++) = (c >= 10) ? (c - 10 + 'a') : (c + '0');
  95 +               c = *src & 0x0f;
  96 +               *(dst++) = (c >= 10) ? (c - 10 + 'a') : (c + '0');
  97 +       }
  98 +       *dst = 0;
  99 +
 100 +       if (asprintf(&dst,"%s/%s",link_by_hash_dir,hash) < 0)
 101 +               out_of_memory("make_hash_name");
 102 +       return dst;
 103 +}
 104 +
 105 +
 106 +void kill_hashfile(struct hashfile_struct *hashfile)
 107 +{
 108 +       if (!hashfile)
 109 +               return;
 110 +       free(hashfile->name);
 111 +       close(hashfile->fd);
 112 +       free(hashfile);
 113 +}
 114 +
 115 +
 116 +void kill_hashfiles(struct hashfile_struct *hashfiles)
 117 +{
 118 +       struct hashfile_struct *iter, *next;
 119 +       if ((iter = hashfiles) != NULL) {
 120 +               do {
 121 +                       next = iter->next;
 122 +                       kill_hashfile(iter);
 123 +                       iter = next;
 124 +               } while (iter != hashfiles);
 125 +       }
 126 +}
 127 +
 128 +
 129 +struct hashfile_struct *find_hashfiles(char *hashname, int64 size, long *fnbr)
 130 +{
 131 +       DIR *d;
 132 +       struct dirent *di;
 133 +       struct hashfile_struct *hashfiles = NULL, *hashfile;
 134 +       STRUCT_STAT st;
 135 +       long this_fnbr;
 136 +
 137 +       *fnbr = 0;
 138 +
 139 +       /* Build a list of potential candidates and open
 140 +        * them. */
 141 +       if ((d = opendir(hashname)) == NULL) {
 142 +               rsyserr(FERROR, errno, "opendir failed: \"%s\"", hashname);
 143 +               free(hashname);
 144 +               return NULL;
 145 +       }
 146 +       while ((di = readdir(d)) != NULL) {
 147 +               if (!strcmp(di->d_name,".") || !strcmp(di->d_name,"..")) {
 148 +                       continue;
 149 +               }
 150 +
 151 +               /* We need to have the largest fnbr in case we need to store
 152 +                * a new file. */
 153 +               this_fnbr = atol(di->d_name);
 154 +               if (this_fnbr > *fnbr)
 155 +                       *fnbr = this_fnbr;
 156 +
 157 +               hashfile = new_array(struct hashfile_struct, 1);
 158 +               if (asprintf(&hashfile->name,"%s/%s",hashname, di->d_name) < 0)
 159 +                       out_of_memory("find_hashfiles");
 160 +               if (do_stat(hashfile->name,&st) == -1) {
 161 +                       rsyserr(FERROR, errno, "stat failed: %s", hashfile->name);
 162 +                       kill_hashfile(hashfile);
 163 +                       continue;
 164 +               }
 165 +               if (st.st_size != size) {
 166 +                       kill_hashfile(hashfile);
 167 +                       continue;
 168 +               }
 169 +               hashfile->nlink = st.st_nlink;
 170 +               hashfile->fd = open(hashfile->name,O_RDONLY|O_BINARY);
 171 +               if (hashfile->fd == -1) {
 172 +                       rsyserr(FERROR, errno, "open failed: %s", hashfile->name);
 173 +                       kill_hashfile(hashfile);
 174 +                       continue;
 175 +               }
 176 +               if (hashfiles == NULL)
 177 +                       hashfiles = hashfile->next = hashfile->prev = hashfile;
 178 +               else {
 179 +                       hashfile->next = hashfiles;
 180 +                       hashfile->prev = hashfiles->prev;
 181 +                       hashfile->next->prev = hashfile;
 182 +                       hashfile->prev->next = hashfile;
 183 +               }
 184 +       }
 185 +       closedir(d);
 186 +
 187 +       return hashfiles;
 188 +}
 189 +
 190 +
 191 +struct hashfile_struct *compare_hashfiles(int fd,struct hashfile_struct *files)
 192 +{
 193 +       int amt, hamt;
 194 +       char buffer[BUFSIZ], cmpbuffer[BUFSIZ];
 195 +       struct hashfile_struct *iter, *next, *best;
 196 +       uint32 nlink;
 197 +
 198 +       if (!files)
 199 +               return NULL;
 200 +
 201 +       iter = files; /* in case files are 0 bytes */
 202 +       while ((amt = read(fd, buffer, BUFSIZ)) > 0) {
 203 +               iter = files;
 204 +               do {
 205 +                       /* Icky bit to resync when we steal the first node. */
 206 +                       if (!files)
 207 +                               files = iter;
 208 +
 209 +                       next = iter->next;
 210 +
 211 +                       hamt = read(iter->fd, cmpbuffer, BUFSIZ);
 212 +                       if (amt != hamt || memcmp(buffer, cmpbuffer, amt)) {
 213 +                               if (iter == files) {
 214 +                                       files = files->prev;
 215 +                               }
 216 +                               if (iter->next == iter) {
 217 +                                       files = next = NULL;
 218 +                               } else {
 219 +                                       next = iter->next;
 220 +                                       if (iter == files) {
 221 +                                               /* So we know to resync */
 222 +                                               files = NULL;
 223 +                                       }
 224 +                               }
 225 +                               iter->next->prev = iter->prev;
 226 +                               iter->prev->next = iter->next;
 227 +                               kill_hashfile(iter);
 228 +                       }
 229 +
 230 +                       iter = next;
 231 +               } while (iter != files);
 232 +
 233 +               if (iter == NULL && files == NULL) {
 234 +                       /* There are no matches. */
 235 +                       return NULL;
 236 +               }
 237 +       }
 238 +
 239 +       if (amt == -1) {
 240 +               rsyserr(FERROR, errno, "read failed in compare_hashfiles()");
 241 +               kill_hashfiles(files);
 242 +               return NULL;
 243 +       }
 244 +
 245 +       /* If we only have one file left, use it. */
 246 +       if (files == files->next) {
 247 +               return files;
 248 +       }
 249 +
 250 +       /* All files which remain in the list are identical and should have
 251 +        * the same size.  We pick the one with the lowest link count (we
 252 +        * may have rolled over because we hit the maximum link count for
 253 +        * the filesystem). */
 254 +       best = iter = files;
 255 +       nlink = iter->nlink;
 256 +       do {
 257 +               if (iter->nlink < nlink) {
 258 +                       nlink = iter->nlink;
 259 +                       best = iter;
 260 +               }
 261 +               iter = iter->next;
 262 +       } while (iter != files);
 263 +
 264 +       best->next->prev = best->prev;
 265 +       best->prev->next = best->next;
 266 +       if (files == best)
 267 +               files = files->next;
 268 +       kill_hashfiles(files);
 269 +       return best;
 270 +}
 271 +
 272 +
 273 +int link_by_hash(const char *fnametmp, const char *fname, struct file_struct *file)
 274 +{
 275 +       STRUCT_STAT st;
 276 +       char *hashname = make_hash_name(file);
 277 +       int first = 0, rc;
 278 +       char *linkname;
 279 +       long last_fnbr;
 280 +
 281 +       if (F_LENGTH(file) == 0)
 282 +               return robust_rename(fnametmp, fname, NULL, 0644);
 283 +
 284 +       if (do_stat(hashname, &st) == -1) {
 285 +               char *dirname;
 286 +
 287 +               /* Directory does not exist. */
 288 +               dirname = strdup(hashname);
 289 +               *strrchr(dirname,'/') = 0;
 290 +               if (do_mkdir(dirname, 0755) == -1 && errno != EEXIST) {
 291 +                       rsyserr(FERROR, errno, "mkdir failed: %s", dirname);
 292 +                       free(hashname);
 293 +                       free(dirname);
 294 +                       return robust_rename(fnametmp, fname, NULL, 0644);
 295 +               }
 296 +               free(dirname);
 297 +
 298 +               if (do_mkdir(hashname, 0755) == -1 && errno != EEXIST) {
 299 +                       rsyserr(FERROR, errno, "mkdir failed: %s", hashname);
 300 +                       free(hashname);
 301 +                       return robust_rename(fnametmp, fname, NULL, 0644);
 302 +               }
 303 +
 304 +               first = 1;
 305 +               if (asprintf(&linkname,"%s/0",hashname) < 0)
 306 +                       out_of_memory("link_by_hash");
 307 +               rprintf(FINFO, "(1) linkname = %s\n", linkname);
 308 +       } else {
 309 +               struct hashfile_struct *hashfiles, *hashfile;
 310 +
 311 +               if (do_stat(fnametmp,&st) == -1) {
 312 +                       rsyserr(FERROR, errno, "stat failed: %s", fname);
 313 +                       return -1;
 314 +               }
 315 +               hashfiles = find_hashfiles(hashname, st.st_size, &last_fnbr);
 316 +
 317 +               if (hashfiles == NULL) {
 318 +                       first = 1;
 319 +                       if (asprintf(&linkname,"%s/0",hashname) < 0)
 320 +                               out_of_memory("link_by_hash");
 321 +                       rprintf(FINFO, "(2) linkname = %s\n", linkname);
 322 +               } else {
 323 +                       int fd;
 324 +                       /* Search for one identical to us. */
 325 +                       if ((fd = open(fnametmp,O_RDONLY|O_BINARY)) == -1) {
 326 +                               rsyserr(FERROR, errno, "open failed: %s", fnametmp);
 327 +                               kill_hashfiles(hashfiles);
 328 +                               return -1;
 329 +                       }
 330 +                       hashfile = compare_hashfiles(fd, hashfiles);
 331 +                       hashfiles = NULL;
 332 +                       close(fd);
 333 +
 334 +                       if (hashfile) {
 335 +                               first = 0;
 336 +                               linkname = strdup(hashfile->name);
 337 +                               rprintf(FINFO, "(3) linkname = %s\n", linkname);
 338 +                               kill_hashfile(hashfile);
 339 +                       } else {
 340 +                               first = 1;
 341 +                               if (asprintf(&linkname, "%s/%ld", hashname, last_fnbr + 1) < 0)
 342 +                                       out_of_memory("link_by_hash");
 343 +                               rprintf(FINFO, "(4) linkname = %s\n", linkname);
 344 +                       }
 345 +               }
 346 +       }
 347 +
 348 +       if (!first) {
 349 +               rprintf(FINFO, "link-by-hash (existing): \"%s\" -> %s\n",
 350 +                               linkname, full_fname(fname));
 351 +               robust_unlink(fname);
 352 +               rc = do_link(linkname, fname);
 353 +               if (rc == -1) {
 354 +                       if (errno == EMLINK) {
 355 +                               first = 1;
 356 +                               free(linkname);
 357 +                               if (asprintf(&linkname,"%s/%ld",hashname, last_fnbr + 1) < 0)
 358 +                                       out_of_memory("link_by_hash");
 359 +                               rprintf(FINFO, "(5) linkname = %s\n", linkname);
 360 +                               rprintf(FINFO,"link-by-hash: max link count exceeded, starting new file \"%s\".\n", linkname);
 361 +                       } else {
 362 +                               rsyserr(FERROR, errno, "link \"%s\" -> \"%s\"",
 363 +                                       linkname, full_fname(fname));
 364 +                               rc = robust_rename(fnametmp, fname, NULL, 0644);
 365 +                       }
 366 +               } else {
 367 +                       do_unlink(fnametmp);
 368 +               }
 369 +       }
 370 +
 371 +       if (first) {
 372 +               rprintf(FINFO, "link-by-hash (new): %s -> \"%s\"\n",
 373 +                               full_fname(fname),linkname);
 374 +
 375 +               rc = robust_rename(fnametmp, fname, NULL, 0644);
 376 +               if (rc != 0) {
 377 +                       rsyserr(FERROR, errno, "rename \"%s\" -> \"%s\"",
 378 +                               full_fname(fnametmp), full_fname(fname));
 379 +               }
 380 +               rc = do_link(fname,linkname);
 381 +               if (rc != 0) {
 382 +                       rsyserr(FERROR, errno, "link \"%s\" -> \"%s\"",
 383 +                               full_fname(fname), linkname);
 384 +               }
 385 +       }
 386 +
 387 +       free(linkname);
 388 +       free(hashname);
 389 +       return rc;
 390 +}
 391 +#endif
 392 diff --git a/options.c b/options.c
 393 --- a/options.c
 394 +++ b/options.c
 395 @@ -158,6 +158,7 @@ char *backup_suffix = NULL;
 396  char *tmpdir = NULL;
 397  char *partial_dir = NULL;
 398  char *basis_dir[MAX_BASIS_DIRS+1];
 399 +char *link_by_hash_dir = NULL;
 400  char *config_file = NULL;
 401  char *shell_cmd = NULL;
 402  char *logfile_name = NULL;
 403 @@ -746,6 +747,7 @@ void usage(enum logcode F)
 404    rprintf(F,"     --compare-dest=DIR      also compare destination files relative to DIR\n");
 405    rprintf(F,"     --copy-dest=DIR         ... and include copies of unchanged files\n");
 406    rprintf(F,"     --link-dest=DIR         hardlink to files in DIR when unchanged\n");
 407 +  rprintf(F,"     --link-by-hash=DIR      create hardlinks by hash into DIR\n");
 408    rprintf(F," -z, --compress              compress file data during the transfer\n");
 409    rprintf(F,"     --compress-level=NUM    explicitly set compression level\n");
 410    rprintf(F,"     --skip-compress=LIST    skip compressing files with a suffix in LIST\n");
 411 @@ -798,7 +800,7 @@ enum {OPT_VERSION = 1000, OPT_DAEMON, OPT_SENDER, OPT_EXCLUDE, OPT_EXCLUDE_FROM,
 412        OPT_FILTER, OPT_COMPARE_DEST, OPT_COPY_DEST, OPT_LINK_DEST, OPT_HELP,
 413        OPT_INCLUDE, OPT_INCLUDE_FROM, OPT_MODIFY_WINDOW, OPT_MIN_SIZE, OPT_CHMOD,
 414        OPT_READ_BATCH, OPT_WRITE_BATCH, OPT_ONLY_WRITE_BATCH, OPT_MAX_SIZE,
 415 -      OPT_NO_D, OPT_APPEND, OPT_NO_ICONV, OPT_INFO, OPT_DEBUG,
 416 +      OPT_NO_D, OPT_APPEND, OPT_NO_ICONV, OPT_INFO, OPT_DEBUG, OPT_LINK_BY_HASH,
 417        OPT_USERMAP, OPT_GROUPMAP, OPT_CHOWN, OPT_BWLIMIT,
 418        OPT_SERVER, OPT_REFUSED_BASE = 9000};
 419
 420 @@ -938,6 +940,7 @@ static struct poptOption long_options[] = {
 421    {"compare-dest",     0,  POPT_ARG_STRING, 0, OPT_COMPARE_DEST, 0, 0 },
 422    {"copy-dest",        0,  POPT_ARG_STRING, 0, OPT_COPY_DEST, 0, 0 },
 423    {"link-dest",        0,  POPT_ARG_STRING, 0, OPT_LINK_DEST, 0, 0 },
 424 +  {"link-by-hash",     0,  POPT_ARG_STRING, 0, OPT_LINK_BY_HASH, 0, 0},
 425    {"fuzzy",           'y', POPT_ARG_VAL,    &fuzzy_basis, 1, 0, 0 },
 426    {"no-fuzzy",         0,  POPT_ARG_VAL,    &fuzzy_basis, 0, 0, 0 },
 427    {"no-y",             0,  POPT_ARG_VAL,    &fuzzy_basis, 0, 0, 0 },
 428 @@ -1763,6 +1766,21 @@ int parse_arguments(int *argc_p, const char ***argv_p)
 429                         return 0;
 430  #endif
 431
 432 +                case OPT_LINK_BY_HASH:
 433 +#ifdef HAVE_LINK
 434 +                       arg = poptGetOptArg(pc);
 435 +                       if (sanitize_paths)
 436 +                               arg = sanitize_path(NULL, arg, NULL, 0, SP_DEFAULT);
 437 +                       link_by_hash_dir = (char *)arg;
 438 +                       break;
 439 +#else
 440 +                       snprintf(err_buf, sizeof err_buf,
 441 +                                "hard links are not supported on this %s\n",
 442 +                                am_server ? "server" : "client");
 443 +                       rprintf(FERROR, "ERROR: %s", err_buf);
 444 +                       return 0;
 445 +#endif
 446 +
 447                 default:
 448                         /* A large opt value means that set_refuse_options()
 449                          * turned this option off. */
 450 @@ -2621,6 +2639,11 @@ void server_options(char **args, int *argc_p)
 451         } else if (inplace)
 452                 args[ac++] = "--inplace";
 453
 454 +       if (link_by_hash_dir && am_sender) {
 455 +               args[ac++] = "--link-by-hash";
 456 +               args[ac++] = link_by_hash_dir;
 457 +       }
 458 +
 459         if (files_from && (!am_sender || filesfrom_host)) {
 460                 if (filesfrom_host) {
 461                         args[ac++] = "--files-from";
 462 diff --git a/receiver.c b/receiver.c
 463 --- a/receiver.c
 464 +++ b/receiver.c
 465 @@ -196,11 +196,13 @@ int open_tmpfile(char *fnametmp, const char *fname, struct file_struct *file)
 466  }
 467
 468  static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 469 -                       const char *fname, int fd, OFF_T total_size)
 470 +                       const char *fname, int fd, OFF_T total_size,
 471 +                       const char *md4)
 472  {
 473         static char file_sum1[MAX_DIGEST_LEN];
 474         struct map_struct *mapbuf;
 475         struct sum_struct sum;
 476 +       md_context mdfour_data;
 477         int32 len;
 478         OFF_T offset = 0;
 479         OFF_T offset2;
 480 @@ -220,6 +222,9 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 481         } else
 482                 mapbuf = NULL;
 483
 484 +       if (md4)
 485 +               mdfour_begin(&mdfour_data);
 486 +
 487         sum_init(checksum_seed);
 488
 489         if (append_mode > 0) {
 490 @@ -264,6 +269,8 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 491                         cleanup_got_literal = 1;
 492
 493                         sum_update(data, i);
 494 +                       if (md4)
 495 +                               mdfour_update(&mdfour_data, (uchar*)data, i);
 496
 497                         if (fd != -1 && write_file(fd,data,i) != i)
 498                                 goto report_write_error;
 499 @@ -290,6 +297,8 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 500
 501                         see_token(map, len);
 502                         sum_update(map, len);
 503 +                       if (md4)
 504 +                               mdfour_update(&mdfour_data, (uchar*)map, len);
 505                 }
 506
 507                 if (updating_basis_or_equiv) {
 508 @@ -337,6 +346,9 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 509         if (sum_end(file_sum1) != checksum_len)
 510                 overflow_exit("checksum_len"); /* Impossible... */
 511
 512 +       if (md4)
 513 +               mdfour_result(&mdfour_data, (uchar*)md4);
 514 +
 515         if (mapbuf)
 516                 unmap_file(mapbuf);
 517
 518 @@ -351,7 +363,7 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 519
 520  static void discard_receive_data(int f_in, OFF_T length)
 521  {
 522 -       receive_data(f_in, NULL, -1, 0, NULL, -1, length);
 523 +       receive_data(f_in, NULL, -1, 0, NULL, -1, length, NULL);
 524  }
 525
 526  static void handle_delayed_updates(char *local_name)
 527 @@ -779,7 +791,7 @@ int recv_files(int f_in, int f_out, char *local_name)
 528
 529                 /* recv file data */
 530                 recv_ok = receive_data(f_in, fnamecmp, fd1, st.st_size,
 531 -                                      fname, fd2, F_LENGTH(file));
 532 +                                      fname, fd2, F_LENGTH(file), F_SUM(file));
 533
 534                 log_item(log_code, file, iflags, NULL);
 535
 536 diff --git a/rsync.c b/rsync.c
 537 --- a/rsync.c
 538 +++ b/rsync.c
 539 @@ -48,6 +48,7 @@ extern int flist_eof;
 540  extern int file_old_total;
 541  extern int keep_dirlinks;
 542  extern int make_backups;
 543 +extern char *link_by_hash_dir;
 544  extern struct file_list *cur_flist, *first_flist, *dir_flist;
 545  extern struct chmod_mode_struct *daemon_chmod_modes;
 546  #ifdef ICONV_OPTION
 547 @@ -644,8 +645,15 @@ int finish_transfer(const char *fname, const char *fnametmp,
 548         /* move tmp file over real file */
 549         if (DEBUG_GTE(RECV, 1))
 550                 rprintf(FINFO, "renaming %s to %s\n", fnametmp, fname);
 551 -       ret = robust_rename(fnametmp, fname, temp_copy_name,
 552 -                           file->mode & INITACCESSPERMS);
 553 +#ifdef HAVE_LINK
 554 +       if (link_by_hash_dir)
 555 +               ret = link_by_hash(fnametmp, fname, file);
 556 +       else
 557 +#endif
 558 +       {
 559 +               ret = robust_rename(fnametmp, fname, temp_copy_name,
 560 +                                   file->mode & INITACCESSPERMS);
 561 +       }
 562         if (ret < 0) {
 563                 rsyserr(FERROR_XFER, errno, "%s %s -> \"%s\"",
 564                         ret == -2 ? "copy" : "rename",
 565 diff --git a/rsync.h b/rsync.h
 566 --- a/rsync.h
 567 +++ b/rsync.h
 568 @@ -865,6 +865,14 @@ struct stats {
 569         int xferred_files;
 570  };
 571
 572 +struct hashfile_struct {
 573 +       struct hashfile_struct *next;
 574 +       struct hashfile_struct *prev;
 575 +       char *name;
 576 +       int fd;
 577 +       uint32 nlink;
 578 +};
 579 +
 580  struct chmod_mode_struct;
 581
 582  struct flist_ndx_item {
 583 diff --git a/rsync.yo b/rsync.yo
 584 --- a/rsync.yo
 585 +++ b/rsync.yo
 586 @@ -400,6 +400,7 @@ to the detailed description below for a complete description.  verb(
 587       --compare-dest=DIR      also compare received files relative to DIR
 588       --copy-dest=DIR         ... and include copies of unchanged files
 589       --link-dest=DIR         hardlink to files in DIR when unchanged
 590 +     --link-by-hash=DIR      create hardlinks by hash into DIR
 591   -z, --compress              compress file data during the transfer
 592       --compress-level=NUM    explicitly set compression level
 593       --skip-compress=LIST    skip compressing files with suffix in LIST