detect-renamed.diff

   1 This patch adds the --detect-renamed option which makes rsync notice files
   2 that either (1) match in size & modify-time (plus the basename, if possible)
   3 or (2) match in size & checksum (when --checksum was also specified) and use
   4 each match as an alternate basis file to speed up the transfer.
   5
   6 The algorithm attempts to scan the receiving-side's files in an efficient
   7 manner.  If --delete[-before] is enabled, we'll take advantage of the
   8 pre-transfer delete pass to prepare any alternate-basis-file matches we
   9 might find.  If --delete-before is not enabled, rsync does the rename scan
  10 during the regular file-sending scan (scanning each directory right before
  11 the generator starts updating files from that dir).  In this latter mode,
  12 rsync might delay the updating of a file (if no alternate-basis match was
  13 yet found) until the full scan of the receiving side is complete, at which
  14 point any delayed files are processed.
  15
  16 I chose to hard-link the alternate-basis files into a ".~tmp~" subdir that
  17 takes advantage of rsync's pre-existing partial-dir logic.  This uses less
  18 memory than trying to keep track of the matches internally, and also allows
  19 any deletions or file-updates to occur normally without interfering with
  20 these alternate-basis discoveries.
  21
  22 After applying this patch, run these commands for a successful build:
  23
  24     ./prepare-source
  25     ./configure                      (optional if already run)
  26     make
  27
  28 TODO:
  29
  30   We need to never return a match from fattr_find() that has a basis
  31   file.  This will ensure that we don't try to give a renamed file to
  32   a file that can't use it, while missing out on giving it to a file
  33   that could use it.
  34
  35 --- old/flist.c
  36 +++ new/flist.c
  37 @@ -56,6 +56,7 @@ extern int implied_dirs;
  38  extern int prune_empty_dirs;
  39  extern int copy_links;
  40  extern int copy_unsafe_links;
  41 +extern int detect_renamed;
  42  extern int protocol_version;
  43  extern int sanitize_paths;
  44  extern const char *io_write_phase;
  45 @@ -74,6 +75,8 @@ int checksum_len;
  46  dev_t filesystem_dev; /* used to implement -x */
  47  unsigned int file_struct_len;
  48
  49 +struct file_list the_fattr_list;
  50 +
  51  static char empty_sum[MD4_SUM_LENGTH];
  52  static int flist_count_offset;
  53
  54 @@ -260,6 +263,44 @@ static mode_t from_wire_mode(int mode)
  55         return (mode_t)mode;
  56  }
  57
  58 +static int fattr_compare(struct file_struct **file1, struct file_struct **file2)
  59 +{
  60 +       struct file_struct *f1 = *file1;
  61 +       struct file_struct *f2 = *file2;
  62 +       int diff;
  63 +
  64 +       if (!f1->basename || !S_ISREG(f1->mode) || !f1->length) {
  65 +               if (!f2->basename || !S_ISREG(f2->mode) || !f2->length)
  66 +                       return 0;
  67 +               return 1;
  68 +       }
  69 +       if (!f2->basename || !S_ISREG(f2->mode) || !f2->length)
  70 +               return -1;
  71 +
  72 +       /* Don't use diff for values that are longer than an int. */
  73 +       if (f1->length != f2->length)
  74 +               return f1->length < f2->length ? -1 : 1;
  75 +
  76 +       if (always_checksum) {
  77 +               diff = u_memcmp(f1->u.sum, f2->u.sum, checksum_len);
  78 +               if (diff)
  79 +                       return diff;
  80 +       } else if (f1->modtime != f2->modtime)
  81 +               return f1->modtime < f2->modtime ? -1 : 1;
  82 +
  83 +       diff = u_strcmp(f1->basename, f2->basename);
  84 +       if (diff)
  85 +               return diff;
  86 +
  87 +       if (f1->dirname == f2->dirname)
  88 +               return 0;
  89 +       if (!f1->dirname)
  90 +               return -1;
  91 +       if (!f2->dirname)
  92 +               return 1;
  93 +       return u_strcmp(f1->dirname, f2->dirname);
  94 +}
  95 +
  96  static void send_directory(int f, struct file_list *flist,
  97                            char *fbuf, int len);
  98
  99 @@ -1388,6 +1429,25 @@ struct file_list *recv_file_list(int f)
 100
 101         clean_flist(flist, relative_paths, 1);
 102
 103 +       if (detect_renamed) {
 104 +               int j = flist->count;
 105 +               the_fattr_list.count = j;
 106 +               the_fattr_list.files = new_array(struct file_struct *, j);
 107 +               if (!the_fattr_list.files)
 108 +                       goto oom;
 109 +               memcpy(the_fattr_list.files, flist->files,
 110 +                      j * sizeof (struct file_struct *));
 111 +               qsort(the_fattr_list.files, j,
 112 +                   sizeof the_fattr_list.files[0], (int (*)())fattr_compare);
 113 +               the_fattr_list.low = 0;
 114 +               while (j-- > 0) {
 115 +                       struct file_struct *fp = the_fattr_list.files[j];
 116 +                       if (fp->basename && S_ISREG(fp->mode) && fp->length)
 117 +                               break;
 118 +               }
 119 +               the_fattr_list.high = j;
 120 +       }
 121 +
 122         if (f >= 0) {
 123                 recv_uid_list(f, flist);
 124
 125 --- old/generator.c
 126 +++ new/generator.c
 127 @@ -77,6 +77,7 @@ extern char *basis_dir[];
 128  extern int compare_dest;
 129  extern int copy_dest;
 130  extern int link_dest;
 131 +extern int detect_renamed;
 132  extern int whole_file;
 133  extern int list_only;
 134  extern int read_batch;
 135 @@ -92,14 +93,17 @@ extern char *backup_dir;
 136  extern char *backup_suffix;
 137  extern int backup_suffix_len;
 138  extern struct file_list *the_file_list;
 139 +extern struct file_list the_fattr_list;
 140  extern struct filter_list_struct server_filter_list;
 141
 142  static int deletion_count = 0; /* used to implement --max-delete */
 143 +static int unexplored_dirs = 1;
 144  static int can_link_symlinks = 1; /* start out optimistic */
 145  static int can_link_devices = 1;
 146
 147 -/* For calling delete_file() */
 148 +/* For calling delete_item() and delete_in_dir() */
 149  #define DEL_FORCE_RECURSE      (1<<1) /* recurse even w/o --force */
 150 +#define DEL_NO_DELETIONS       (1<<2)
 151  #define DEL_TERSE              (1<<3)
 152
 153
 154 @@ -109,12 +113,120 @@ static int is_backup_file(char *fn)
 155         return k > 0 && strcmp(fn+k, backup_suffix) == 0;
 156  }
 157
 158 +/* Search for a regular file that matches either (1) the size & modified
 159 + * time (plus the basename, if possible) or (2) the size & checksum.  If
 160 + * we find an exact match down to the dirname, return -1 because we found
 161 + * an up-to-date file in the transfer, not a renamed file. */
 162 +static int fattr_find(struct file_struct *f, char *fname, alloc_pool_t pool)
 163 +{
 164 +       int low = the_fattr_list.low, high = the_fattr_list.high;
 165 +       int mid, ok_match = -1, good_match = -1;
 166 +       struct file_struct *fmid;
 167 +       int diff;
 168 +
 169 +       while (low <= high) {
 170 +               mid = (low + high) / 2;
 171 +               fmid = the_fattr_list.files[mid];
 172 +               if (fmid->length != f->length) {
 173 +                       if (fmid->length < f->length)
 174 +                               low = mid + 1;
 175 +                       else
 176 +                               high = mid - 1;
 177 +                       continue;
 178 +               }
 179 +               if (always_checksum) {
 180 +                       if (!f->u.sum) {
 181 +                               if (fmid->modtime == f->modtime
 182 +                                && f_name_cmp(fmid, f) == 0)
 183 +                                       return -1; /* assume we can't help */
 184 +                               f->u.sum = pool_alloc(pool, MD4_SUM_LENGTH,
 185 +                                                     "fattr_find");
 186 +                               file_checksum(fname, f->u.sum, f->length);
 187 +                       }
 188 +                       diff = u_memcmp(fmid->u.sum, f->u.sum, checksum_len);
 189 +                       if (diff) {
 190 +                               if (diff < 0)
 191 +                                       low = mid + 1;
 192 +                               else
 193 +                                       high = mid - 1;
 194 +                               continue;
 195 +                       }
 196 +               } else {
 197 +                       if (fmid->modtime != f->modtime) {
 198 +                               if (fmid->modtime < f->modtime)
 199 +                                       low = mid + 1;
 200 +                               else
 201 +                                       high = mid - 1;
 202 +                               continue;
 203 +                       }
 204 +               }
 205 +               ok_match = mid;
 206 +               diff = u_strcmp(fmid->basename, f->basename);
 207 +               if (diff == 0) {
 208 +                       good_match = mid;
 209 +                       if (fmid->dirname == f->dirname)
 210 +                               return -1; /* file is up-to-date */
 211 +                       if (!fmid->dirname) {
 212 +                               low = mid + 1;
 213 +                               continue;
 214 +                       }
 215 +                       if (!f->dirname) {
 216 +                               high = mid - 1;
 217 +                               continue;
 218 +                       }
 219 +                       diff = u_strcmp(fmid->dirname, f->dirname);
 220 +                       if (diff == 0)
 221 +                               return -1; /* file is up-to-date */
 222 +               }
 223 +               if (diff < 0)
 224 +                       low = mid + 1;
 225 +               else
 226 +                       high = mid - 1;
 227 +       }
 228 +
 229 +       return good_match >= 0 ? good_match : ok_match;
 230 +}
 231 +
 232 +static void look_for_rename(struct file_struct *file, char *fname,
 233 +                           alloc_pool_t pool)
 234 +{
 235 +       struct file_struct *fp;
 236 +       char *partialptr, *fn;
 237 +       STRUCT_STAT st;
 238 +       int ndx;
 239 +
 240 +       if ((ndx = fattr_find(file, fname, pool)) < 0)
 241 +               return;
 242 +
 243 +       fp = the_fattr_list.files[ndx];
 244 +       fn = f_name(fp, NULL);
 245 +       /* We don't provide an alternate-basis file if there is a basis file. */
 246 +       if (link_stat(fn, &st, 0) == 0)
 247 +               return;
 248 +       if ((partialptr = partial_dir_fname(fn)) == NULL
 249 +        || !handle_partial_dir(partialptr, PDIR_CREATE))
 250 +               return;
 251 +
 252 +       /* We only use the file if we can hard-link it into our tmp dir. */
 253 +       if (link(fname, partialptr) == 0) {
 254 +               if (verbose > 2) {
 255 +                       rprintf(FINFO, "found renamed: %s => %s\n",
 256 +                               fname, partialptr);
 257 +               }
 258 +               return;
 259 +       }
 260 +
 261 +       if (errno != EEXIST)
 262 +               handle_partial_dir(partialptr, PDIR_DELETE);
 263 +}
 264
 265  /* Delete a file or directory.  If DEL_FORCE_RECURSE is set in the flags, or if
 266   * force_delete is set, this will delete recursively.
 267   *
 268   * Note that fname must point to a MAXPATHLEN buffer if the mode indicates it's
 269   * a directory! (The buffer is used for recursion, but returned unchanged.)
 270 + *
 271 + * Also Note:  --detect-rename may use this routine with DEL_NO_DELETIONS set!
 272   */
 273  static int delete_item(char *fname, int mode, int flags)
 274  {
 275 @@ -125,6 +237,8 @@ static int delete_item(char *fname, int
 276         char *p;
 277
 278         if (!S_ISDIR(mode)) {
 279 +               if (flags & DEL_NO_DELETIONS)
 280 +                       return 0;
 281                 if (max_delete && ++deletion_count > max_delete)
 282                         return 0;
 283                 if (make_backups && (backup_dir || !is_backup_file(fname)))
 284 @@ -147,6 +261,7 @@ static int delete_item(char *fname, int
 285
 286         zap_dir = flags & DEL_FORCE_RECURSE || force_delete;
 287         if ((max_delete && ++deletion_count > max_delete)
 288 +           || flags & DEL_NO_DELETIONS
 289             || (dry_run && zap_dir)) {
 290                 ok = 0;
 291                 errno = ENOTEMPTY;
 292 @@ -189,6 +304,8 @@ static int delete_item(char *fname, int
 293                         continue;
 294
 295                 strlcpy(p, fp->basename, remainder);
 296 +               if (detect_renamed && S_ISREG(fp->mode))
 297 +                       look_for_rename(fp, fname, dirlist->file_pool);
 298                 delete_item(fname, fp->mode, flags & ~DEL_TERSE);
 299         }
 300         flist_free(dirlist);
 301 @@ -197,7 +314,8 @@ static int delete_item(char *fname, int
 302
 303         pop_local_filters(save_filters);
 304
 305 -       if (max_delete && ++deletion_count > max_delete)
 306 +       if (flags & DEL_NO_DELETIONS
 307 +        || (max_delete && ++deletion_count > max_delete))
 308                 return 0;
 309
 310         if (do_rmdir(fname) == 0) {
 311 @@ -217,15 +335,19 @@ static int delete_item(char *fname, int
 312   * all the --delete-WHEN options.  Note that the fbuf pointer must point to a
 313   * MAXPATHLEN buffer with the name of the directory in it (the functions we
 314   * call will append names onto the end, but the old dir value will be restored
 315 - * on exit). */
 316 + * on exit).
 317 + *
 318 + * Note:  --detect-rename may use this routine with DEL_NO_DELETIONS set!
 319 + */
 320  static void delete_in_dir(struct file_list *flist, char *fbuf,
 321 -                         struct file_struct *file, STRUCT_STAT *stp)
 322 +                         struct file_struct *file, STRUCT_STAT *stp, int flags)
 323  {
 324         static int min_depth = MAXPATHLEN, cur_depth = -1;
 325         static void *filt_array[MAXPATHLEN/2+1];
 326         static int already_warned = 0;
 327         struct file_list *dirlist;
 328 -       char delbuf[MAXPATHLEN];
 329 +       char *p, delbuf[MAXPATHLEN];
 330 +       unsigned remainder;
 331         int dlen, i;
 332
 333         if (!flist) {
 334 @@ -239,6 +361,8 @@ static void delete_in_dir(struct file_li
 335         if (verbose > 2)
 336                 rprintf(FINFO, "delete_in_dir(%s)\n", fbuf);
 337
 338 +       flags |= DEL_FORCE_RECURSE;
 339 +
 340         if (allowed_lull)
 341                 maybe_send_keepalive();
 342
 343 @@ -246,12 +370,14 @@ static void delete_in_dir(struct file_li
 344                 return; /* Impossible... */
 345
 346         if (io_error && !(lp_ignore_errors(module_id) || ignore_errors)) {
 347 -               if (already_warned)
 348 +               if (!already_warned) {
 349 +                       rprintf(FINFO,
 350 +                           "IO error encountered -- skipping file deletion\n");
 351 +                       already_warned = 1;
 352 +               }
 353 +               if (!detect_renamed)
 354                         return;
 355 -               rprintf(FINFO,
 356 -                       "IO error encountered -- skipping file deletion\n");
 357 -               already_warned = 1;
 358 -               return;
 359 +               flags |= DEL_NO_DELETIONS;
 360         }
 361
 362         while (cur_depth >= file->dir.depth && cur_depth >= min_depth)
 363 @@ -262,6 +388,9 @@ static void delete_in_dir(struct file_li
 364         dlen = strlen(fbuf);
 365         filt_array[cur_depth] = push_local_filters(fbuf, dlen);
 366
 367 +       if (detect_renamed)
 368 +               unexplored_dirs--;
 369 +
 370         if (one_file_system) {
 371                 if (file->flags & FLAG_TOP_DIR)
 372                         filesystem_dev = stp->st_dev;
 373 @@ -271,18 +400,30 @@ static void delete_in_dir(struct file_li
 374
 375         dirlist = get_dirlist(fbuf, dlen, 0);
 376
 377 +       p = fbuf + dlen;
 378 +       if (dlen != 1 || *fbuf != '/')
 379 +               *p++ = '/';
 380 +       remainder = MAXPATHLEN - (p - fbuf);
 381 +
 382         /* If an item in dirlist is not found in flist, delete it
 383          * from the filesystem. */
 384         for (i = dirlist->count; i--; ) {
 385                 struct file_struct *fp = dirlist->files[i];
 386                 if (!fp->basename || fp->flags & FLAG_MOUNT_POINT)
 387                         continue;
 388 +               if (detect_renamed && S_ISREG(fp->mode)) {
 389 +                       strlcpy(p, fp->basename, remainder);
 390 +                       look_for_rename(fp, fbuf, dirlist->file_pool);
 391 +               }
 392                 if (flist_find(flist, fp) < 0) {
 393                         f_name(fp, delbuf);
 394 -                       delete_item(delbuf, fp->mode, DEL_FORCE_RECURSE);
 395 -               }
 396 +                       delete_item(delbuf, fp->mode, flags);
 397 +               } else if (detect_renamed && S_ISDIR(fp->mode))
 398 +                       unexplored_dirs++;
 399         }
 400
 401 +       fbuf[dlen] = '\0';
 402 +
 403         flist_free(dirlist);
 404  }
 405
 406 @@ -312,9 +453,9 @@ static void do_delete_pass(struct file_l
 407                  || !S_ISDIR(st.st_mode))
 408                         continue;
 409
 410 -               delete_in_dir(flist, fbuf, file, &st);
 411 +               delete_in_dir(flist, fbuf, file, &st, 0);
 412         }
 413 -       delete_in_dir(NULL, NULL, NULL, NULL);
 414 +       delete_in_dir(NULL, NULL, NULL, NULL, 0);
 415
 416         if (do_progress && !am_server)
 417                 rprintf(FINFO, "                    \r");
 418 @@ -753,6 +894,7 @@ static int try_dests_non(struct file_str
 419         return -1;
 420  }
 421
 422 +static struct bitbag *delayed_bits = NULL;
 423  static int phase = 0;
 424
 425  /* Acts on the_file_list->file's ndx'th item, whose name is fname.  If a dir,
 426 @@ -894,8 +1036,12 @@ static void recv_generator(char *fname,
 427                     && verbose && code && f_out != -1)
 428                         rprintf(code, "%s/\n", fname);
 429                 if (delete_during && f_out != -1 && !phase && dry_run < 2
 430 -                   && (file->flags & FLAG_DEL_HERE))
 431 -                       delete_in_dir(the_file_list, fname, file, &st);
 432 +                   && (file->flags & FLAG_DEL_HERE)) {
 433 +                       if (detect_renamed && statret != 0)
 434 +                               unexplored_dirs++;
 435 +                       delete_in_dir(the_file_list, fname, file, &st,
 436 +                                     delete_during < 0 ? DEL_NO_DELETIONS : 0);
 437 +               }
 438                 return;
 439         }
 440
 441 @@ -1133,8 +1279,14 @@ static void recv_generator(char *fname,
 442                     && hard_link_check(file, ndx, fname, statret, &st,
 443                                        itemizing, code, HL_SKIP))
 444                         return;
 445 -               if (stat_errno == ENOENT)
 446 +               if (stat_errno == ENOENT) {
 447 +                       if (detect_renamed && unexplored_dirs > 0
 448 +                        && file->length) {
 449 +                               bitbag_set_bit(delayed_bits, ndx);
 450 +                               return;
 451 +                       }
 452                         goto notify_others;
 453 +               }
 454                 rsyserr(FERROR, stat_errno, "recv_generator: failed to stat %s",
 455                         full_fname(fname));
 456                 return;
 457 @@ -1309,11 +1461,17 @@ void generate_files(int f_out, struct fi
 458                         (long)getpid(), flist->count);
 459         }
 460
 461 +       if (detect_renamed) {
 462 +               delayed_bits = bitbag_create(flist->count);
 463 +               if (!delete_before && !delete_during)
 464 +                       delete_during = -1;
 465 +       }
 466 +
 467         if (delete_before && !local_name && flist->count > 0)
 468                 do_delete_pass(flist);
 469         do_progress = 0;
 470
 471 -       if (append_mode || whole_file < 0)
 472 +       if (append_mode || detect_renamed || whole_file < 0)
 473                 whole_file = 0;
 474         if (verbose >= 2) {
 475                 rprintf(FINFO, "delta-transmission %s\n",
 476 @@ -1368,7 +1526,23 @@ void generate_files(int f_out, struct fi
 477         }
 478         recv_generator(NULL, NULL, 0, 0, 0, code, -1);
 479         if (delete_during)
 480 -               delete_in_dir(NULL, NULL, NULL, NULL);
 481 +               delete_in_dir(NULL, NULL, NULL, NULL, 0);
 482 +
 483 +       if (detect_renamed) {
 484 +               if (delete_during < 0)
 485 +                       delete_during = 0;
 486 +               detect_renamed = 0;
 487 +
 488 +               for (i = -1; (i = bitbag_next_bit(delayed_bits, i)) >= 0; ) {
 489 +                       struct file_struct *file = flist->files[i];
 490 +                       if (local_name)
 491 +                               strlcpy(fbuf, local_name, sizeof fbuf);
 492 +                       else
 493 +                               f_name(file, fbuf);
 494 +                       recv_generator(fbuf, file, i, itemizing,
 495 +                                      maybe_ATTRS_REPORT, code, f_out);
 496 +               }
 497 +       }
 498
 499         phase++;
 500         csum_length = SUM_LENGTH;
 501 --- old/options.c
 502 +++ new/options.c
 503 @@ -78,6 +78,7 @@ int am_starting_up = 1;
 504  int orig_umask = 0;
 505  int relative_paths = -1;
 506  int implied_dirs = 1;
 507 +int detect_renamed = 0;
 508  int numeric_ids = 0;
 509  int allow_8bit_chars = 0;
 510  int force_delete = 0;
 511 @@ -335,6 +336,7 @@ void usage(enum logcode F)
 512    rprintf(F,"     --modify-window=NUM     compare mod-times with reduced accuracy\n");
 513    rprintf(F," -T, --temp-dir=DIR          create temporary files in directory DIR\n");
 514    rprintf(F," -y, --fuzzy                 find similar file for basis if no dest file\n");
 515 +  rprintf(F,"     --detect-renamed        try to find renamed files to speed up the transfer\n");
 516    rprintf(F,"     --compare-dest=DIR      also compare destination files relative to DIR\n");
 517    rprintf(F,"     --copy-dest=DIR         ... and include copies of unchanged files\n");
 518    rprintf(F,"     --link-dest=DIR         hardlink to files in DIR when unchanged\n");
 519 @@ -480,6 +482,7 @@ static struct poptOption long_options[]
 520    {"compare-dest",     0,  POPT_ARG_STRING, 0, OPT_COMPARE_DEST, 0, 0 },
 521    {"copy-dest",        0,  POPT_ARG_STRING, 0, OPT_COPY_DEST, 0, 0 },
 522    {"link-dest",        0,  POPT_ARG_STRING, 0, OPT_LINK_DEST, 0, 0 },
 523 +  {"detect-renamed",   0,  POPT_ARG_NONE,   &detect_renamed, 0, 0, 0 },
 524    {"fuzzy",           'y', POPT_ARG_NONE,   &fuzzy_basis, 0, 0, 0 },
 525    {"compress",        'z', POPT_ARG_NONE,   0, 'z', 0, 0 },
 526    {"compress-level",   0,  POPT_ARG_INT,    &def_compress_level, 'z', 0, 0 },
 527 @@ -1335,7 +1338,7 @@ int parse_arguments(int *argc, const cha
 528                 inplace = 1;
 529         }
 530
 531 -       if (delay_updates && !partial_dir)
 532 +       if ((delay_updates || detect_renamed) && !partial_dir)
 533                 partial_dir = tmp_partialdir;
 534
 535         if (inplace) {
 536 @@ -1344,6 +1347,7 @@ int parse_arguments(int *argc, const cha
 537                         snprintf(err_buf, sizeof err_buf,
 538                                  "--%s cannot be used with --%s\n",
 539                                  append_mode ? "append" : "inplace",
 540 +                                detect_renamed ? "detect-renamed" :
 541                                  delay_updates ? "delay-updates" : "partial-dir");
 542                         return 0;
 543                 }
 544 --- old/rsync.yo
 545 +++ new/rsync.yo
 546 @@ -358,6 +358,7 @@ to the detailed description below for a
 547       --modify-window=NUM     compare mod-times with reduced accuracy
 548   -T, --temp-dir=DIR          create temporary files in directory DIR
 549   -y, --fuzzy                 find similar file for basis if no dest file
 550 +     --detect-renamed        try to find renamed files to speed the xfer
 551       --compare-dest=DIR      also compare received files relative to DIR
 552       --copy-dest=DIR         ... and include copies of unchanged files
 553       --link-dest=DIR         hardlink to files in DIR when unchanged
 554 @@ -1183,6 +1184,15 @@ Note that the use of the bf(--delete) op
 555  fuzzy-match files, so either use bf(--delete-after) or specify some
 556  filename exclusions if you need to prevent this.
 557
 558 +dit(bf(--detect-renamed)) This option tells rsync to scan the receiving
 559 +side for files that have been renamed, and to use any that are found as
 560 +alternate basis files to help speed up the transfer.
 561 +By default, alternate-basis files are hard-linked into a directory named
 562 +".~tmp~" in each file's destination directory, but if you've specified
 563 +the bf(--partial-dir) option, that directory will be used instead.  These
 564 +potential alternate-basis files will be removed as the transfer progresses.
 565 +This option conflicts with bf(--inplace) and bf(--append).
 566 +
 567  dit(bf(--compare-dest=DIR)) This option instructs rsync to use em(DIR) on
 568  the destination machine as an additional hierarchy to compare destination
 569  files against doing transfers (if the files are missing in the destination
 570 --- old/util.c
 571 +++ new/util.c
 572 @@ -997,6 +997,32 @@ int handle_partial_dir(const char *fname
 573         return 1;
 574  }
 575
 576 +/* We need to supply our own strcmp function for file list comparisons
 577 + * to ensure that signed/unsigned usage is consistent between machines. */
 578 +int u_strcmp(const char *p1, const char *p2)
 579 +{
 580 +        for ( ; *p1; p1++, p2++) {
 581 +               if (*p1 != *p2)
 582 +                       break;
 583 +       }
 584 +
 585 +       return (int)*(uchar*)p1 - (int)*(uchar*)p2;
 586 +}
 587 +
 588 +/* We need a memcmp function compares unsigned-byte values. */
 589 +int u_memcmp(const void *p1, const void *p2, size_t len)
 590 +{
 591 +       const uchar *u1 = p1;
 592 +       const uchar *u2 = p2;
 593 +
 594 +       while (len--) {
 595 +               if (*u1 != *u2)
 596 +                       return (int)*u1 - (int)*u2;
 597 +       }
 598 +
 599 +       return 0;
 600 +}
 601 +
 602  /**
 603   * Determine if a symlink points outside the current directory tree.
 604   * This is considered "unsafe" because e.g. when mirroring somebody