db/hash/FreeBSD/hash_bigkey.c

   1 /*-
   2  * Copyright (c) 1990, 1993, 1994
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Margo Seltzer.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  */
  36
  37 #if defined(LIBC_SCCS) && !defined(lint)
  38 static char sccsid[] = "@(#)hash_bigkey.c       8.3 (Berkeley) 5/31/94";
  39 #endif /* LIBC_SCCS and not lint */
  40 #include <sys/cdefs.h>
  41 __FBSDID("$FreeBSD: src/lib/libc/db/hash/hash_bigkey.c,v 1.5 2003/02/16 17:29:09 nectar Exp $");
  42
  43 /*
  44  * PACKAGE: hash
  45  * DESCRIPTION:
  46  *      Big key/data handling for the hashing package.
  47  *
  48  * ROUTINES:
  49  * External
  50  *      __big_keydata
  51  *      __big_split
  52  *      __big_insert
  53  *      __big_return
  54  *      __big_delete
  55  *      __find_last_page
  56  * Internal
  57  *      collect_key
  58  *      collect_data
  59  */
  60
  61 #include <sys/param.h>
  62
  63 #include <errno.h>
  64 #include <stdio.h>
  65 #include <stdlib.h>
  66 #include <string.h>
  67
  68 #ifdef DEBUG
  69 #include <assert.h>
  70 #endif
  71
  72 #include <db.h>
  73 #include "hash.h"
  74 #include "page.h"
  75 #include "extern.h"
  76
  77 static int collect_key(HTAB *, BUFHEAD *, int, DBT *, int);
  78 static int collect_data(HTAB *, BUFHEAD *, int, int);
  79
  80 /*
  81  * Big_insert
  82  *
  83  * You need to do an insert and the key/data pair is too big
  84  *
  85  * Returns:
  86  * 0 ==> OK
  87  *-1 ==> ERROR
  88  */
  89 extern int
  90 __big_insert(hashp, bufp, key, val)
  91         HTAB *hashp;
  92         BUFHEAD *bufp;
  93         const DBT *key, *val;
  94 {
  95         u_int16_t *p;
  96         int key_size, n, val_size;
  97         u_int16_t space, move_bytes, off;
  98         char *cp, *key_data, *val_data;
  99
 100         cp = bufp->page;                /* Character pointer of p. */
 101         p = (u_int16_t *)cp;
 102
 103         key_data = (char *)key->data;
 104         key_size = key->size;
 105         val_data = (char *)val->data;
 106         val_size = val->size;
 107
 108         /* First move the Key */
 109         for (space = FREESPACE(p) - BIGOVERHEAD; key_size;
 110             space = FREESPACE(p) - BIGOVERHEAD) {
 111                 move_bytes = MIN(space, key_size);
 112                 off = OFFSET(p) - move_bytes;
 113                 memmove(cp + off, key_data, move_bytes);
 114                 key_size -= move_bytes;
 115                 key_data += move_bytes;
 116                 n = p[0];
 117                 p[++n] = off;
 118                 p[0] = ++n;
 119                 FREESPACE(p) = off - PAGE_META(n);
 120                 OFFSET(p) = off;
 121                 p[n] = PARTIAL_KEY;
 122                 bufp = __add_ovflpage(hashp, bufp);
 123                 if (!bufp)
 124                         return (-1);
 125                 n = p[0];
 126                 if (!key_size) {
 127                         if (FREESPACE(p)) {
 128                                 move_bytes = MIN(FREESPACE(p), val_size);
 129                                 off = OFFSET(p) - move_bytes;
 130                                 p[n] = off;
 131                                 memmove(cp + off, val_data, move_bytes);
 132                                 val_data += move_bytes;
 133                                 val_size -= move_bytes;
 134                                 p[n - 2] = FULL_KEY_DATA;
 135                                 FREESPACE(p) = FREESPACE(p) - move_bytes;
 136                                 OFFSET(p) = off;
 137                         } else
 138                                 p[n - 2] = FULL_KEY;
 139                 }
 140                 p = (u_int16_t *)bufp->page;
 141                 cp = bufp->page;
 142                 bufp->flags |= BUF_MOD;
 143         }
 144
 145         /* Now move the data */
 146         for (space = FREESPACE(p) - BIGOVERHEAD; val_size;
 147             space = FREESPACE(p) - BIGOVERHEAD) {
 148                 move_bytes = MIN(space, val_size);
 149                 /*
 150                  * Here's the hack to make sure that if the data ends on the
 151                  * same page as the key ends, FREESPACE is at least one.
 152                  */
 153                 if (space == val_size && val_size == val->size)
 154                         move_bytes--;
 155                 off = OFFSET(p) - move_bytes;
 156                 memmove(cp + off, val_data, move_bytes);
 157                 val_size -= move_bytes;
 158                 val_data += move_bytes;
 159                 n = p[0];
 160                 p[++n] = off;
 161                 p[0] = ++n;
 162                 FREESPACE(p) = off - PAGE_META(n);
 163                 OFFSET(p) = off;
 164                 if (val_size) {
 165                         p[n] = FULL_KEY;
 166                         bufp = __add_ovflpage(hashp, bufp);
 167                         if (!bufp)
 168                                 return (-1);
 169                         cp = bufp->page;
 170                         p = (u_int16_t *)cp;
 171                 } else
 172                         p[n] = FULL_KEY_DATA;
 173                 bufp->flags |= BUF_MOD;
 174         }
 175         return (0);
 176 }
 177
 178 /*
 179  * Called when bufp's page  contains a partial key (index should be 1)
 180  *
 181  * All pages in the big key/data pair except bufp are freed.  We cannot
 182  * free bufp because the page pointing to it is lost and we can't get rid
 183  * of its pointer.
 184  *
 185  * Returns:
 186  * 0 => OK
 187  *-1 => ERROR
 188  */
 189 extern int
 190 __big_delete(hashp, bufp)
 191         HTAB *hashp;
 192         BUFHEAD *bufp;
 193 {
 194         BUFHEAD *last_bfp, *rbufp;
 195         u_int16_t *bp, pageno;
 196         int key_done, n;
 197
 198         rbufp = bufp;
 199         last_bfp = NULL;
 200         bp = (u_int16_t *)bufp->page;
 201         pageno = 0;
 202         key_done = 0;
 203
 204         while (!key_done || (bp[2] != FULL_KEY_DATA)) {
 205                 if (bp[2] == FULL_KEY || bp[2] == FULL_KEY_DATA)
 206                         key_done = 1;
 207
 208                 /*
 209                  * If there is freespace left on a FULL_KEY_DATA page, then
 210                  * the data is short and fits entirely on this page, and this
 211                  * is the last page.
 212                  */
 213                 if (bp[2] == FULL_KEY_DATA && FREESPACE(bp))
 214                         break;
 215                 pageno = bp[bp[0] - 1];
 216                 rbufp->flags |= BUF_MOD;
 217                 rbufp = __get_buf(hashp, pageno, rbufp, 0);
 218                 if (last_bfp)
 219                         __free_ovflpage(hashp, last_bfp);
 220                 last_bfp = rbufp;
 221                 if (!rbufp)
 222                         return (-1);            /* Error. */
 223                 bp = (u_int16_t *)rbufp->page;
 224         }
 225
 226         /*
 227          * If we get here then rbufp points to the last page of the big
 228          * key/data pair.  Bufp points to the first one -- it should now be
 229          * empty pointing to the next page after this pair.  Can't free it
 230          * because we don't have the page pointing to it.
 231          */
 232
 233         /* This is information from the last page of the pair. */
 234         n = bp[0];
 235         pageno = bp[n - 1];
 236
 237         /* Now, bp is the first page of the pair. */
 238         bp = (u_int16_t *)bufp->page;
 239         if (n > 2) {
 240                 /* There is an overflow page. */
 241                 bp[1] = pageno;
 242                 bp[2] = OVFLPAGE;
 243                 bufp->ovfl = rbufp->ovfl;
 244         } else
 245                 /* This is the last page. */
 246                 bufp->ovfl = NULL;
 247         n -= 2;
 248         bp[0] = n;
 249         FREESPACE(bp) = hashp->BSIZE - PAGE_META(n);
 250         OFFSET(bp) = hashp->BSIZE - 1;
 251
 252         bufp->flags |= BUF_MOD;
 253         if (rbufp)
 254                 __free_ovflpage(hashp, rbufp);
 255         if (last_bfp != rbufp)
 256                 __free_ovflpage(hashp, last_bfp);
 257
 258         hashp->NKEYS--;
 259         return (0);
 260 }
 261 /*
 262  * Returns:
 263  *  0 = key not found
 264  * -1 = get next overflow page
 265  * -2 means key not found and this is big key/data
 266  * -3 error
 267  */
 268 extern int
 269 __find_bigpair(hashp, bufp, ndx, key, size)
 270         HTAB *hashp;
 271         BUFHEAD *bufp;
 272         int ndx;
 273         char *key;
 274         int size;
 275 {
 276         u_int16_t *bp;
 277         char *p;
 278         int ksize;
 279         u_int16_t bytes;
 280         char *kkey;
 281
 282         bp = (u_int16_t *)bufp->page;
 283         p = bufp->page;
 284         ksize = size;
 285         kkey = key;
 286
 287         for (bytes = hashp->BSIZE - bp[ndx];
 288             bytes <= size && bp[ndx + 1] == PARTIAL_KEY;
 289             bytes = hashp->BSIZE - bp[ndx]) {
 290                 if (memcmp(p + bp[ndx], kkey, bytes))
 291                         return (-2);
 292                 kkey += bytes;
 293                 ksize -= bytes;
 294                 bufp = __get_buf(hashp, bp[ndx + 2], bufp, 0);
 295                 if (!bufp)
 296                         return (-3);
 297                 p = bufp->page;
 298                 bp = (u_int16_t *)p;
 299                 ndx = 1;
 300         }
 301
 302         if (bytes != ksize || memcmp(p + bp[ndx], kkey, bytes)) {
 303 #ifdef HASH_STATISTICS
 304                 ++hash_collisions;
 305 #endif
 306                 return (-2);
 307         } else
 308                 return (ndx);
 309 }
 310
 311 /*
 312  * Given the buffer pointer of the first overflow page of a big pair,
 313  * find the end of the big pair
 314  *
 315  * This will set bpp to the buffer header of the last page of the big pair.
 316  * It will return the pageno of the overflow page following the last page
 317  * of the pair; 0 if there isn't any (i.e. big pair is the last key in the
 318  * bucket)
 319  */
 320 extern u_int16_t
 321 __find_last_page(hashp, bpp)
 322         HTAB *hashp;
 323         BUFHEAD **bpp;
 324 {
 325         BUFHEAD *bufp;
 326         u_int16_t *bp, pageno;
 327         int n;
 328
 329         bufp = *bpp;
 330         bp = (u_int16_t *)bufp->page;
 331         for (;;) {
 332                 n = bp[0];
 333
 334                 /*
 335                  * This is the last page if: the tag is FULL_KEY_DATA and
 336                  * either only 2 entries OVFLPAGE marker is explicit there
 337                  * is freespace on the page.
 338                  */
 339                 if (bp[2] == FULL_KEY_DATA &&
 340                     ((n == 2) || (bp[n] == OVFLPAGE) || (FREESPACE(bp))))
 341                         break;
 342
 343                 pageno = bp[n - 1];
 344                 bufp = __get_buf(hashp, pageno, bufp, 0);
 345                 if (!bufp)
 346                         return (0);     /* Need to indicate an error! */
 347                 bp = (u_int16_t *)bufp->page;
 348         }
 349
 350         *bpp = bufp;
 351         if (bp[0] > 2)
 352                 return (bp[3]);
 353         else
 354                 return (0);
 355 }
 356
 357 /*
 358  * Return the data for the key/data pair that begins on this page at this
 359  * index (index should always be 1).
 360  */
 361 extern int
 362 __big_return(hashp, bufp, ndx, val, set_current)
 363         HTAB *hashp;
 364         BUFHEAD *bufp;
 365         int ndx;
 366         DBT *val;
 367         int set_current;
 368 {
 369         BUFHEAD *save_p;
 370         u_int16_t *bp, len, off, save_addr;
 371         char *tp;
 372
 373         bp = (u_int16_t *)bufp->page;
 374         while (bp[ndx + 1] == PARTIAL_KEY) {
 375                 bufp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 376                 if (!bufp)
 377                         return (-1);
 378                 bp = (u_int16_t *)bufp->page;
 379                 ndx = 1;
 380         }
 381
 382         if (bp[ndx + 1] == FULL_KEY) {
 383                 bufp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 384                 if (!bufp)
 385                         return (-1);
 386                 bp = (u_int16_t *)bufp->page;
 387                 save_p = bufp;
 388                 save_addr = save_p->addr;
 389                 off = bp[1];
 390                 len = 0;
 391         } else
 392                 if (!FREESPACE(bp)) {
 393                         /*
 394                          * This is a hack.  We can't distinguish between
 395                          * FULL_KEY_DATA that contains complete data or
 396                          * incomplete data, so we require that if the data
 397                          * is complete, there is at least 1 byte of free
 398                          * space left.
 399                          */
 400                         off = bp[bp[0]];
 401                         len = bp[1] - off;
 402                         save_p = bufp;
 403                         save_addr = bufp->addr;
 404                         bufp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 405                         if (!bufp)
 406                                 return (-1);
 407                         bp = (u_int16_t *)bufp->page;
 408                 } else {
 409                         /* The data is all on one page. */
 410                         tp = (char *)bp;
 411                         off = bp[bp[0]];
 412                         val->data = (u_char *)tp + off;
 413                         val->size = bp[1] - off;
 414                         if (set_current) {
 415                                 if (bp[0] == 2) {       /* No more buckets in
 416                                                          * chain */
 417                                         hashp->cpage = NULL;
 418                                         hashp->cbucket++;
 419                                         hashp->cndx = 1;
 420                                 } else {
 421                                         hashp->cpage = __get_buf(hashp,
 422                                             bp[bp[0] - 1], bufp, 0);
 423                                         if (!hashp->cpage)
 424                                                 return (-1);
 425                                         hashp->cndx = 1;
 426                                         if (!((u_int16_t *)
 427                                             hashp->cpage->page)[0]) {
 428                                                 hashp->cbucket++;
 429                                                 hashp->cpage = NULL;
 430                                         }
 431                                 }
 432                         }
 433                         return (0);
 434                 }
 435
 436         val->size = collect_data(hashp, bufp, (int)len, set_current);
 437         if (val->size == -1)
 438                 return (-1);
 439         if (save_p->addr != save_addr) {
 440                 /* We are pretty short on buffers. */
 441                 errno = EINVAL;                 /* OUT OF BUFFERS */
 442                 return (-1);
 443         }
 444         memmove(hashp->tmp_buf, (save_p->page) + off, len);
 445         val->data = (u_char *)hashp->tmp_buf;
 446         return (0);
 447 }
 448 /*
 449  * Count how big the total datasize is by recursing through the pages.  Then
 450  * allocate a buffer and copy the data as you recurse up.
 451  */
 452 static int
 453 collect_data(hashp, bufp, len, set)
 454         HTAB *hashp;
 455         BUFHEAD *bufp;
 456         int len, set;
 457 {
 458         u_int16_t *bp;
 459         char *p;
 460         BUFHEAD *xbp;
 461         u_int16_t save_addr;
 462         int mylen, totlen;
 463
 464         p = bufp->page;
 465         bp = (u_int16_t *)p;
 466         mylen = hashp->BSIZE - bp[1];
 467         save_addr = bufp->addr;
 468
 469         if (bp[2] == FULL_KEY_DATA) {           /* End of Data */
 470                 totlen = len + mylen;
 471                 if (hashp->tmp_buf)
 472                         free(hashp->tmp_buf);
 473                 if ((hashp->tmp_buf = (char *)malloc(totlen)) == NULL)
 474                         return (-1);
 475                 if (set) {
 476                         hashp->cndx = 1;
 477                         if (bp[0] == 2) {       /* No more buckets in chain */
 478                                 hashp->cpage = NULL;
 479                                 hashp->cbucket++;
 480                         } else {
 481                                 hashp->cpage =
 482                                     __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 483                                 if (!hashp->cpage)
 484                                         return (-1);
 485                                 else if (!((u_int16_t *)hashp->cpage->page)[0]) {
 486                                         hashp->cbucket++;
 487                                         hashp->cpage = NULL;
 488                                 }
 489                         }
 490                 }
 491         } else {
 492                 xbp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 493                 if (!xbp || ((totlen =
 494                     collect_data(hashp, xbp, len + mylen, set)) < 1))
 495                         return (-1);
 496         }
 497         if (bufp->addr != save_addr) {
 498                 errno = EINVAL;                 /* Out of buffers. */
 499                 return (-1);
 500         }
 501         memmove(&hashp->tmp_buf[len], (bufp->page) + bp[1], mylen);
 502         return (totlen);
 503 }
 504
 505 /*
 506  * Fill in the key and data for this big pair.
 507  */
 508 extern int
 509 __big_keydata(hashp, bufp, key, val, set)
 510         HTAB *hashp;
 511         BUFHEAD *bufp;
 512         DBT *key, *val;
 513         int set;
 514 {
 515         key->size = collect_key(hashp, bufp, 0, val, set);
 516         if (key->size == -1)
 517                 return (-1);
 518         key->data = (u_char *)hashp->tmp_key;
 519         return (0);
 520 }
 521
 522 /*
 523  * Count how big the total key size is by recursing through the pages.  Then
 524  * collect the data, allocate a buffer and copy the key as you recurse up.
 525  */
 526 static int
 527 collect_key(hashp, bufp, len, val, set)
 528         HTAB *hashp;
 529         BUFHEAD *bufp;
 530         int len;
 531         DBT *val;
 532         int set;
 533 {
 534         BUFHEAD *xbp;
 535         char *p;
 536         int mylen, totlen;
 537         u_int16_t *bp, save_addr;
 538
 539         p = bufp->page;
 540         bp = (u_int16_t *)p;
 541         mylen = hashp->BSIZE - bp[1];
 542
 543         save_addr = bufp->addr;
 544         totlen = len + mylen;
 545         if (bp[2] == FULL_KEY || bp[2] == FULL_KEY_DATA) {    /* End of Key. */
 546                 if (hashp->tmp_key != NULL)
 547                         free(hashp->tmp_key);
 548                 if ((hashp->tmp_key = (char *)malloc(totlen)) == NULL)
 549                         return (-1);
 550                 if (__big_return(hashp, bufp, 1, val, set))
 551                         return (-1);
 552         } else {
 553                 xbp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
 554                 if (!xbp || ((totlen =
 555                     collect_key(hashp, xbp, totlen, val, set)) < 1))
 556                         return (-1);
 557         }
 558         if (bufp->addr != save_addr) {
 559                 errno = EINVAL;         /* MIS -- OUT OF BUFFERS */
 560                 return (-1);
 561         }
 562         memmove(&hashp->tmp_key[len], (bufp->page) + bp[1], mylen);
 563         return (totlen);
 564 }
 565
 566 /*
 567  * Returns:
 568  *  0 => OK
 569  * -1 => error
 570  */
 571 extern int
 572 __big_split(hashp, op, np, big_keyp, addr, obucket, ret)
 573         HTAB *hashp;
 574         BUFHEAD *op;    /* Pointer to where to put keys that go in old bucket */
 575         BUFHEAD *np;    /* Pointer to new bucket page */
 576                         /* Pointer to first page containing the big key/data */
 577         BUFHEAD *big_keyp;
 578         int addr;       /* Address of big_keyp */
 579         u_int32_t   obucket;/* Old Bucket */
 580         SPLIT_RETURN *ret;
 581 {
 582         BUFHEAD *tmpp;
 583         u_int16_t *tp;
 584         BUFHEAD *bp;
 585         DBT key, val;
 586         u_int32_t change;
 587         u_int16_t free_space, n, off;
 588
 589         bp = big_keyp;
 590
 591         /* Now figure out where the big key/data goes */
 592         if (__big_keydata(hashp, big_keyp, &key, &val, 0))
 593                 return (-1);
 594         change = (__call_hash(hashp, key.data, key.size) != obucket);
 595
 596         if ( (ret->next_addr = __find_last_page(hashp, &big_keyp)) ) {
 597                 if (!(ret->nextp =
 598                     __get_buf(hashp, ret->next_addr, big_keyp, 0)))
 599                         return (-1);;
 600         } else
 601                 ret->nextp = NULL;
 602
 603         /* Now make one of np/op point to the big key/data pair */
 604 #ifdef DEBUG
 605         assert(np->ovfl == NULL);
 606 #endif
 607         if (change)
 608                 tmpp = np;
 609         else
 610                 tmpp = op;
 611
 612         tmpp->flags |= BUF_MOD;
 613 #ifdef DEBUG1
 614         (void)fprintf(stderr,
 615             "BIG_SPLIT: %d->ovfl was %d is now %d\n", tmpp->addr,
 616             (tmpp->ovfl ? tmpp->ovfl->addr : 0), (bp ? bp->addr : 0));
 617 #endif
 618         tmpp->ovfl = bp;        /* one of op/np point to big_keyp */
 619         tp = (u_int16_t *)tmpp->page;
 620 #ifdef DEBUG
 621         assert(FREESPACE(tp) >= OVFLSIZE);
 622 #endif
 623         n = tp[0];
 624         off = OFFSET(tp);
 625         free_space = FREESPACE(tp);
 626         tp[++n] = (u_int16_t)addr;
 627         tp[++n] = OVFLPAGE;
 628         tp[0] = n;
 629         OFFSET(tp) = off;
 630         FREESPACE(tp) = free_space - OVFLSIZE;
 631
 632         /*
 633          * Finally, set the new and old return values. BIG_KEYP contains a
 634          * pointer to the last page of the big key_data pair. Make sure that
 635          * big_keyp has no following page (2 elements) or create an empty
 636          * following page.
 637          */
 638
 639         ret->newp = np;
 640         ret->oldp = op;
 641
 642         tp = (u_int16_t *)big_keyp->page;
 643         big_keyp->flags |= BUF_MOD;
 644         if (tp[0] > 2) {
 645                 /*
 646                  * There may be either one or two offsets on this page.  If
 647                  * there is one, then the overflow page is linked on normally
 648                  * and tp[4] is OVFLPAGE.  If there are two, tp[4] contains
 649                  * the second offset and needs to get stuffed in after the
 650                  * next overflow page is added.
 651                  */
 652                 n = tp[4];
 653                 free_space = FREESPACE(tp);
 654                 off = OFFSET(tp);
 655                 tp[0] -= 2;
 656                 FREESPACE(tp) = free_space + OVFLSIZE;
 657                 OFFSET(tp) = off;
 658                 tmpp = __add_ovflpage(hashp, big_keyp);
 659                 if (!tmpp)
 660                         return (-1);
 661                 tp[4] = n;
 662         } else
 663                 tmpp = big_keyp;
 664
 665         if (change)
 666                 ret->newp = tmpp;
 667         else
 668                 ret->oldp = tmpp;
 669         return (0);
 670 }