hash_page.c

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/*-
 * Copyright (c) 1990, 1993, 1994
 * The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Margo Seltzer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 * This product includes software developed by the University of
 * California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)hash_page.c   8.7 (Berkeley) 8/16/94";
#endif /* LIBC_SCCS and not lint */

/*
 * PACKAGE:  hashing
 *
 * DESCRIPTION:
 * Page manipulation for hashing package.
 *
 * ROUTINES:
 *
 * External
 * __get_page
 * __add_ovflpage
 * Internal
 * overflow_page
 * open_temp
 */

#include <sys/types.h>

#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#ifdef DEBUG
#include <assert.h>
#endif

#include "../include/db.h"
#include "hash.h"
#include "page.h"
#include "extern.h"

static u_int32_t  *fetch_bitmap __P((HTAB *, int));
static u_int32_t   first_free __P((u_int32_t));
static int   open_temp __P((HTAB *));
static u_int16_t   overflow_page __P((HTAB *));
static void  putpair __P((char *, const DBT *, const DBT *));
static void  squeeze_key __P((u_int16_t *, const DBT *, const DBT *));
static int   ugly_split
          __P((HTAB *, u_int32_t, BUFHEAD *, BUFHEAD *, int, int));

#define  PAGE_INIT(P) { \
   ((u_int16_t *)(P))[0] = 0; \
   ((u_int16_t *)(P))[1] = hashp->BSIZE - 3 * sizeof(u_int16_t); \
   ((u_int16_t *)(P))[2] = hashp->BSIZE; \
}

/*
 * This is called AFTER we have verified that there is room on the page for
 * the pair (PAIRFITS has returned true) so we go right ahead and start moving
 * stuff on.
 */
static void
putpair(p, key, val)
   char *p;
   const DBT *key, *val;
{
   register u_int16_t *bp, n, off;

   bp = (u_int16_t *)p;

   /* Enter the key first. */
   n = bp[0];

   off = OFFSET(bp) - key->size;
   memmove(p + off, key->data, key->size);
   bp[++n] = off;

   /* Now the data. */
   off -= val->size;
   memmove(p + off, val->data, val->size);
   bp[++n] = off;

   /* Adjust page info. */
   bp[0] = n;
   bp[n + 1] = off - ((n + 3) * sizeof(u_int16_t));
   bp[n + 2] = off;
}

/*
 * Returns:
 *  0 OK
 * -1 error
 */
extern int
__delpair(hashp, bufp, ndx)
   HTAB *hashp;
   BUFHEAD *bufp;
   register int ndx;
{
   register u_int16_t *bp, newoff;
   register int n;
   u_int16_t pairlen;

   bp = (u_int16_t *)bufp->page;
   n = bp[0];

   if (bp[ndx + 1] < REAL_KEY)
      return (__big_delete(hashp, bufp));
   if (ndx != 1)
      newoff = bp[ndx - 1];
   else
      newoff = hashp->BSIZE;
   pairlen = newoff - bp[ndx + 1];

   if (ndx != (n - 1)) {
      /* Hard Case -- need to shuffle keys */
      register int i;
      register char *src = bufp->page + (int)OFFSET(bp);
      register char *dst = src + (int)pairlen;
      memmove(dst, src, bp[ndx + 1] - OFFSET(bp));

      /* Now adjust the pointers */
      for (i = ndx + 2; i <= n; i += 2) {
         if (bp[i + 1] == OVFLPAGE) {
            bp[i - 2] = bp[i];
            bp[i - 1] = bp[i + 1];
         } else {
            bp[i - 2] = bp[i] + pairlen;
            bp[i - 1] = bp[i + 1] + pairlen;
         }
      }
   }
   /* Finally adjust the page data */
   bp[n] = OFFSET(bp) + pairlen;
   bp[n - 1] = bp[n + 1] + pairlen + 2 * sizeof(u_int16_t);
   bp[0] = n - 2;
   hashp->NKEYS--;

   bufp->flags |= BUF_MOD;
   return (0);
}
/*
 * Returns:
 *  0 ==> OK
 * -1 ==> Error
 */
extern int
__split_page(hashp, obucket, nbucket)
   HTAB *hashp;
   u_int32_t obucket, nbucket;
{
   register BUFHEAD *new_bufp, *old_bufp;
   register u_int16_t *ino;
   register char *np;
   DBT key, val;
   int n, ndx, retval;
   u_int16_t copyto, diff, off, moved;
   char *op;

   copyto = (u_int16_t)hashp->BSIZE;
   off = (u_int16_t)hashp->BSIZE;
   old_bufp = __get_buf(hashp, obucket, NULL, 0);
   if (old_bufp == NULL)
      return (-1);
   new_bufp = __get_buf(hashp, nbucket, NULL, 0);
   if (new_bufp == NULL)
      return (-1);

   old_bufp->flags |= (BUF_MOD | BUF_PIN);
   new_bufp->flags |= (BUF_MOD | BUF_PIN);

   ino = (u_int16_t *)(op = old_bufp->page);
   np = new_bufp->page;

   moved = 0;

   for (n = 1, ndx = 1; n < ino[0]; n += 2) {
      if (ino[n + 1] < REAL_KEY) {
         retval = ugly_split(hashp, obucket, old_bufp, new_bufp,
             (int)copyto, (int)moved);
         old_bufp->flags &= ~BUF_PIN;
         new_bufp->flags &= ~BUF_PIN;
         return (retval);

      }
      key.data = (u_char *)op + ino[n];
      key.size = off - ino[n];

      if (__call_hash(hashp, key.data, key.size) == obucket) {
         /* Don't switch page */
         diff = copyto - off;
         if (diff) {
            copyto = ino[n + 1] + diff;
            memmove(op + copyto, op + ino[n + 1],
                off - ino[n + 1]);
            ino[ndx] = copyto + ino[n] - ino[n + 1];
            ino[ndx + 1] = copyto;
         } else
            copyto = ino[n + 1];
         ndx += 2;
      } else {
         /* Switch page */
         val.data = (u_char *)op + ino[n + 1];
         val.size = ino[n] - ino[n + 1];
         putpair(np, &key, &val);
         moved += 2;
      }

      off = ino[n + 1];
   }

   /* Now clean up the page */
   ino[0] -= moved;
   FREESPACE(ino) = copyto - sizeof(u_int16_t) * (ino[0] + 3);
   OFFSET(ino) = copyto;

#ifdef DEBUG3
   (void)fprintf(stderr, "split %d/%d\n",
       ((u_int16_t *)np)[0] / 2,
       ((u_int16_t *)op)[0] / 2);
#endif
   /* unpin both pages */
   old_bufp->flags &= ~BUF_PIN;
   new_bufp->flags &= ~BUF_PIN;
   return (0);
}

/*
 * Called when we encounter an overflow or big key/data page during split
 * handling.  This is special cased since we have to begin checking whether
 * the key/data pairs fit on their respective pages and because we may need
 * overflow pages for both the old and new pages.
 *
 * The first page might be a page with regular key/data pairs in which case
 * we have a regular overflow condition and just need to go on to the next
 * page or it might be a big key/data pair in which case we need to fix the
 * big key/data pair.
 *
 * Returns:
 *  0 ==> success
 * -1 ==> failure
 */
static int
ugly_split(hashp, obucket, old_bufp, new_bufp, copyto, moved)
   HTAB *hashp;
   u_int32_t obucket;   /* Same as __split_page. */
   BUFHEAD *old_bufp, *new_bufp;
   int copyto; /* First byte on page which contains key/data values. */
   int moved;  /* Number of pairs moved to new page. */
{
   register BUFHEAD *bufp; /* Buffer header for ino */
   register u_int16_t *ino;   /* Page keys come off of */
   register u_int16_t *np; /* New page */
   register u_int16_t *op; /* Page keys go on to if they aren't moving */

   BUFHEAD *last_bfp;   /* Last buf header OVFL needing to be freed */
   DBT key, val;
   SPLIT_RETURN ret;
   u_int16_t n, off, ov_addr, scopyto;
   char *cino;    /* Character value of ino */

   bufp = old_bufp;
   ino = (u_int16_t *)old_bufp->page;
   np = (u_int16_t *)new_bufp->page;
   op = (u_int16_t *)old_bufp->page;
   last_bfp = NULL;
   scopyto = (u_int16_t)copyto;  /* ANSI */

   n = ino[0] - 1;
   while (n < ino[0]) {
      if (ino[2] < REAL_KEY && ino[2] != OVFLPAGE) {
         if (__big_split(hashp, old_bufp,
             new_bufp, bufp, bufp->addr, obucket, &ret))
            return (-1);
         old_bufp = ret.oldp;
         if (!old_bufp)
            return (-1);
         op = (u_int16_t *)old_bufp->page;
         new_bufp = ret.newp;
         if (!new_bufp)
            return (-1);
         np = (u_int16_t *)new_bufp->page;
         bufp = ret.nextp;
         if (!bufp)
            return (0);
         cino = (char *)bufp->page;
         ino = (u_int16_t *)cino;
         last_bfp = ret.nextp;
      } else if (ino[n + 1] == OVFLPAGE) {
         ov_addr = ino[n];
         /*
          * Fix up the old page -- the extra 2 are the fields
          * which contained the overflow information.
          */
         ino[0] -= (moved + 2);
         FREESPACE(ino) =
             scopyto - sizeof(u_int16_t) * (ino[0] + 3);
         OFFSET(ino) = scopyto;

         bufp = __get_buf(hashp, ov_addr, bufp, 0);
         if (!bufp)
            return (-1);

         ino = (u_int16_t *)bufp->page;
         n = 1;
         scopyto = hashp->BSIZE;
         moved = 0;

         if (last_bfp)
            __free_ovflpage(hashp, last_bfp);
         last_bfp = bufp;
      }
      /* Move regular sized pairs of there are any */
      off = hashp->BSIZE;
      for (n = 1; (n < ino[0]) && (ino[n + 1] >= REAL_KEY); n += 2) {
         cino = (char *)ino;
         key.data = (u_char *)cino + ino[n];
         key.size = off - ino[n];
         val.data = (u_char *)cino + ino[n + 1];
         val.size = ino[n] - ino[n + 1];
         off = ino[n + 1];

         if (__call_hash(hashp, key.data, key.size) == obucket) {
            /* Keep on old page */
            if (PAIRFITS(op, (&key), (&val)))
               putpair((char *)op, &key, &val);
            else {
               old_bufp =
                   __add_ovflpage(hashp, old_bufp);
               if (!old_bufp)
                  return (-1);
               op = (u_int16_t *)old_bufp->page;
               putpair((char *)op, &key, &val);
            }
            old_bufp->flags |= BUF_MOD;
         } else {
            /* Move to new page */
            if (PAIRFITS(np, (&key), (&val)))
               putpair((char *)np, &key, &val);
            else {
               new_bufp =
                   __add_ovflpage(hashp, new_bufp);
               if (!new_bufp)
                  return (-1);
               np = (u_int16_t *)new_bufp->page;
               putpair((char *)np, &key, &val);
            }
            new_bufp->flags |= BUF_MOD;
         }
      }
   }
   if (last_bfp)
      __free_ovflpage(hashp, last_bfp);
   return (0);
}

/*
 * Add the given pair to the page
 *
 * Returns:
 * 0 ==> OK
 * 1 ==> failure
 */
extern int
__addel(hashp, bufp, key, val)
   HTAB *hashp;
   BUFHEAD *bufp;
   const DBT *key, *val;
{
   register u_int16_t *bp, *sop;
   int do_expand;

   bp = (u_int16_t *)bufp->page;
   do_expand = 0;
   while (bp[0] && (bp[2] < REAL_KEY || bp[bp[0]] < REAL_KEY))
      /* Exception case */
      if (bp[2] == FULL_KEY_DATA && bp[0] == 2)
         /* This is the last page of a big key/data pair
            and we need to add another page */
         break;
      else if (bp[2] < REAL_KEY && bp[bp[0]] != OVFLPAGE) {
         bufp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
         if (!bufp)
            return (-1);
         bp = (u_int16_t *)bufp->page;
      } else
         /* Try to squeeze key on this page */
         if (FREESPACE(bp) > PAIRSIZE(key, val)) {
            squeeze_key(bp, key, val);
            return (0);
         } else {
            bufp = __get_buf(hashp, bp[bp[0] - 1], bufp, 0);
            if (!bufp)
               return (-1);
            bp = (u_int16_t *)bufp->page;
         }

   if (PAIRFITS(bp, key, val))
      putpair(bufp->page, key, val);
   else {
      do_expand = 1;
      bufp = __add_ovflpage(hashp, bufp);
      if (!bufp)
         return (-1);
      sop = (u_int16_t *)bufp->page;

      if (PAIRFITS(sop, key, val))
         putpair((char *)sop, key, val);
      else
         if (__big_insert(hashp, bufp, key, val))
            return (-1);
   }
   bufp->flags |= BUF_MOD;
   /*
    * If the average number of keys per bucket exceeds the fill factor,
    * expand the table.
    */
   hashp->NKEYS++;
   if (do_expand ||
       (hashp->NKEYS / (hashp->MAX_BUCKET + 1) > hashp->FFACTOR))
      return (__expand_table(hashp));
   return (0);
}

/*
 *
 * Returns:
 * pointer on success
 * NULL on error
 */
extern BUFHEAD *
__add_ovflpage(hashp, bufp)
   HTAB *hashp;
   BUFHEAD *bufp;
{
   register u_int16_t *sp;
   u_int16_t ndx, ovfl_num;
#ifdef DEBUG1
   int tmp1, tmp2;
#endif
   sp = (u_int16_t *)bufp->page;

   /* Check if we are dynamically determining the fill factor */
   if (hashp->FFACTOR == DEF_FFACTOR) {
      hashp->FFACTOR = sp[0] >> 1;
      if (hashp->FFACTOR < MIN_FFACTOR)
         hashp->FFACTOR = MIN_FFACTOR;
   }
   bufp->flags |= BUF_MOD;
   ovfl_num = overflow_page(hashp);
#ifdef DEBUG1
   tmp1 = bufp->addr;
   tmp2 = bufp->ovfl ? bufp->ovfl->addr : 0;
#endif
   if (!ovfl_num || !(bufp->ovfl = __get_buf(hashp, ovfl_num, bufp, 1)))
      return (NULL);
   bufp->ovfl->flags |= BUF_MOD;
#ifdef DEBUG1
   (void)fprintf(stderr, "ADDOVFLPAGE: %d->ovfl was %d is now %d\n",
       tmp1, tmp2, bufp->ovfl->addr);
#endif
   ndx = sp[0];
   /*
    * Since a pair is allocated on a page only if there's room to add
    * an overflow page, we know that the OVFL information will fit on
    * the page.
    */
   sp[ndx + 4] = OFFSET(sp);
   sp[ndx + 3] = FREESPACE(sp) - OVFLSIZE;
   sp[ndx + 1] = ovfl_num;
   sp[ndx + 2] = OVFLPAGE;
   sp[0] = ndx + 2;
#ifdef HASH_STATISTICS
   hash_overflows++;
#endif
   return (bufp->ovfl);
}

/*
 * Returns:
 *  0 indicates SUCCESS
 * -1 indicates FAILURE
 */
extern int
__get_page(hashp, p, bucket, is_bucket, is_disk, is_bitmap)
   HTAB *hashp;
   char *p;
   u_int32_t bucket;
   int is_bucket, is_disk, is_bitmap;
{
   register int fd, page, size;
   int rsize;
   u_int16_t *bp;

   fd = hashp->fp;
   size = hashp->BSIZE;

   if ((fd == -1) || !is_disk) {
      PAGE_INIT(p);
      return (0);
   }
   if (is_bucket)
      page = BUCKET_TO_PAGE(bucket);
   else
      page = OADDR_TO_PAGE(bucket);
   if ((lseek(fd, (off_t)page << hashp->BSHIFT, SEEK_SET) == -1) ||
       ((rsize = read(fd, p, size)) == -1))
      return (-1);
   bp = (u_int16_t *)p;
   if (!rsize)
      bp[0] = 0;  /* We hit the EOF, so initialize a new page */
   else
      if (rsize != size) {
         errno = EFTYPE;
         return (-1);
      }
   if (!is_bitmap && !bp[0]) {
      PAGE_INIT(p);
   } else
      if (hashp->LORDER != BYTE_ORDER) {
         register int i, max;

         if (is_bitmap) {
            max = hashp->BSIZE >> 2; /* divide by 4 */
            for (i = 0; i < max; i++)
               M_32_SWAP(((int *)p)[i]);
         } else {
            M_16_SWAP(bp[0]);
            max = bp[0] + 2;
            for (i = 1; i <= max; i++)
               M_16_SWAP(bp[i]);
         }
      }
   return (0);
}

/*
 * Write page p to disk
 *
 * Returns:
 *  0 ==> OK
 * -1 ==>failure
 */
extern int
__put_page(hashp, p, bucket, is_bucket, is_bitmap)
   HTAB *hashp;
   char *p;
   u_int32_t bucket;
   int is_bucket, is_bitmap;
{
   register int fd, page, size;
   int wsize;

   size = hashp->BSIZE;
   if ((hashp->fp == -1) && open_temp(hashp))
      return (-1);
   fd = hashp->fp;

   if (hashp->LORDER != BYTE_ORDER) {
      register int i;
      register int max;

      if (is_bitmap) {
         max = hashp->BSIZE >> 2;   /* divide by 4 */
         for (i = 0; i < max; i++)
            M_32_SWAP(((int *)p)[i]);
      } else {
         max = ((u_int16_t *)p)[0] + 2;
         for (i = 0; i <= max; i++)
            M_16_SWAP(((u_int16_t *)p)[i]);
      }
   }
   if (is_bucket)
      page = BUCKET_TO_PAGE(bucket);
   else
      page = OADDR_TO_PAGE(bucket);
   if ((lseek(fd, (off_t)page << hashp->BSHIFT, SEEK_SET) == -1) ||
       ((wsize = write(fd, p, size)) == -1))
      /* Errno is set */
      return (-1);
   if (wsize != size) {
      errno = EFTYPE;
      return (-1);
   }
   return (0);
}

#define BYTE_MASK ((1 << INT_BYTE_SHIFT) -1)
/*
 * Initialize a new bitmap page.  Bitmap pages are left in memory
 * once they are read in.
 */
extern int
__ibitmap(hashp, pnum, nbits, ndx)
   HTAB *hashp;
   int pnum, nbits, ndx;
{
   u_int32_t *ip;
   int clearbytes, clearints;

   if ((ip = (u_int32_t *)malloc(hashp->BSIZE)) == NULL)
      return (1);
   hashp->nmaps++;
   clearints = ((nbits - 1) >> INT_BYTE_SHIFT) + 1;
   clearbytes = clearints << INT_TO_BYTE;
   (void)memset((char *)ip, 0, clearbytes);
   (void)memset(((char *)ip) + clearbytes, 0xFF,
       hashp->BSIZE - clearbytes);
   ip[clearints - 1] = ALL_SET << (nbits & BYTE_MASK);
   SETBIT(ip, 0);
   hashp->BITMAPS[ndx] = (u_int16_t)pnum;
   hashp->mapp[ndx] = ip;
   return (0);
}

static u_int32_t
first_free(map)
   u_int32_t map;
{
   register u_int32_t i, mask;

   mask = 0x1;
   for (i = 0; i < BITS_PER_MAP; i++) {
      if (!(mask & map))
         return (i);
      mask = mask << 1;
   }
   return (i);
}

static u_int16_t
overflow_page(hashp)
   HTAB *hashp;
{
   register u_int32_t *freep = 0;
   register int max_free, offset, splitnum;
   u_int16_t addr;
   int bit, first_page, free_bit, free_page, i, in_use_bits, j;
#ifdef DEBUG2
   int tmp1, tmp2;
#endif
   splitnum = hashp->OVFL_POINT;
   max_free = hashp->SPARES[splitnum];

   free_page = (max_free - 1) >> (hashp->BSHIFT + BYTE_SHIFT);
   free_bit = (max_free - 1) & ((hashp->BSIZE << BYTE_SHIFT) - 1);

   /* Look through all the free maps to find the first free block */
   first_page = hashp->LAST_FREED >>(hashp->BSHIFT + BYTE_SHIFT);
   for ( i = first_page; i <= free_page; i++ ) {
      if (!(freep = (u_int32_t *)hashp->mapp[i]) &&
          !(freep = fetch_bitmap(hashp, i)))
         return (0);
      if (i == free_page)
         in_use_bits = free_bit;
      else
         in_use_bits = (hashp->BSIZE << BYTE_SHIFT) - 1;

      if (i == first_page) {
         bit = hashp->LAST_FREED &
             ((hashp->BSIZE << BYTE_SHIFT) - 1);
         j = bit / BITS_PER_MAP;
         bit = bit & ~(BITS_PER_MAP - 1);
      } else {
         bit = 0;
         j = 0;
      }
      for (; bit <= in_use_bits; j++, bit += BITS_PER_MAP)
         if (freep[j] != ALL_SET)
            goto found;
   }

   /* No Free Page Found */
   hashp->LAST_FREED = hashp->SPARES[splitnum];
   hashp->SPARES[splitnum]++;
   offset = hashp->SPARES[splitnum] -
       (splitnum ? hashp->SPARES[splitnum - 1] : 0);

#define  OVMSG "HASH: Out of overflow pages.  Increase page size\n"
   if (offset > SPLITMASK) {
      if (++splitnum >= NCACHED) {
         if (write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1) < 0) {
         }
         return (0);
      }
      hashp->OVFL_POINT = splitnum;
      hashp->SPARES[splitnum] = hashp->SPARES[splitnum-1];
      hashp->SPARES[splitnum-1]--;
      offset = 1;
   }

   /* Check if we need to allocate a new bitmap page */
   if (free_bit == (hashp->BSIZE << BYTE_SHIFT) - 1) {
      free_page++;
      if (free_page >= NCACHED) {
         if (write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1) < 0) {
         }
         return (0);
      }
      /*
       * This is tricky.  The 1 indicates that you want the new page
       * allocated with 1 clear bit.  Actually, you are going to
       * allocate 2 pages from this map.  The first is going to be
       * the map page, the second is the overflow page we were
       * looking for.  The init_bitmap routine automatically, sets
       * the first bit of itself to indicate that the bitmap itself
       * is in use.  We would explicitly set the second bit, but
       * don't have to if we tell init_bitmap not to leave it clear
       * in the first place.
       */
      if (__ibitmap(hashp,
          (int)OADDR_OF(splitnum, offset), 1, free_page))
         return (0);
      hashp->SPARES[splitnum]++;
#ifdef DEBUG2
      free_bit = 2;
#endif
      offset++;
      if (offset > SPLITMASK) {
         if (++splitnum >= NCACHED) {
            if (write(STDERR_FILENO, OVMSG, sizeof(OVMSG) - 1) < 0) {
            }
            return (0);
         }
         hashp->OVFL_POINT = splitnum;
         hashp->SPARES[splitnum] = hashp->SPARES[splitnum-1];
         hashp->SPARES[splitnum-1]--;
         offset = 0;
      }
   } else {
      /*
       * Free_bit addresses the last used bit.  Bump it to address
       * the first available bit.
       */
      free_bit++;
      SETBIT(freep, free_bit);
   }

   /* Calculate address of the new overflow page */
   addr = OADDR_OF(splitnum, offset);
#ifdef DEBUG2
   (void)fprintf(stderr, "OVERFLOW_PAGE: ADDR: %d BIT: %d PAGE %d\n",
       addr, free_bit, free_page);
#endif
   return (addr);

found:
   bit = bit + first_free(freep[j]);
   SETBIT(freep, bit);
#ifdef DEBUG2
   tmp1 = bit;
   tmp2 = i;
#endif
   /*
    * Bits are addressed starting with 0, but overflow pages are addressed
    * beginning at 1. Bit is a bit addressnumber, so we need to increment
    * it to convert it to a page number.
    */
   bit = 1 + bit + (i * (hashp->BSIZE << BYTE_SHIFT));
   if (bit >= hashp->LAST_FREED)
      hashp->LAST_FREED = bit - 1;

   /* Calculate the split number for this page */
   for (i = 0; (i < splitnum) && (bit > hashp->SPARES[i]); i++);
   offset = (i ? bit - hashp->SPARES[i - 1] : bit);
   if (offset >= SPLITMASK)
      return (0); /* Out of overflow pages */
   addr = OADDR_OF(i, offset);
#ifdef DEBUG2
   (void)fprintf(stderr, "OVERFLOW_PAGE: ADDR: %d BIT: %d PAGE %d\n",
       addr, tmp1, tmp2);
#endif

   /* Allocate and return the overflow page */
   return (addr);
}

/*
 * Mark this overflow page as free.
 */
extern void
__free_ovflpage(hashp, obufp)
   HTAB *hashp;
   BUFHEAD *obufp;
{
   register u_int16_t addr;
   u_int32_t *freep;
   int bit_address, free_page, free_bit;
   u_int16_t ndx;

   addr = obufp->addr;
#ifdef DEBUG1
   (void)fprintf(stderr, "Freeing %d\n", addr);
#endif
   ndx = (((u_int16_t)addr) >> SPLITSHIFT);
   bit_address =
       (ndx ? hashp->SPARES[ndx - 1] : 0) + (addr & SPLITMASK) - 1;
    if (bit_address < hashp->LAST_FREED)
      hashp->LAST_FREED = bit_address;
   free_page = (bit_address >> (hashp->BSHIFT + BYTE_SHIFT));
   free_bit = bit_address & ((hashp->BSIZE << BYTE_SHIFT) - 1);

   if (!(freep = hashp->mapp[free_page]))
      freep = fetch_bitmap(hashp, free_page);
#ifdef DEBUG
   /*
    * This had better never happen.  It means we tried to read a bitmap
    * that has already had overflow pages allocated off it, and we
    * failed to read it from the file.
    */
   if (!freep)
      assert(0);
#endif
   CLRBIT(freep, free_bit);
#ifdef DEBUG2
   (void)fprintf(stderr, "FREE_OVFLPAGE: ADDR: %d BIT: %d PAGE %d\n",
       obufp->addr, free_bit, free_page);
#endif
   __reclaim_buf(hashp, obufp);
}

/*
 * Returns:
 *  0 success
 * -1 failure
 */
static int
open_temp(hashp)
   HTAB *hashp;
{
   sigset_t set, oset;
   static char namestr[] = "_hashXXXXXX";

   /* Block signals; make sure file goes away at process exit. */
   (void)sigfillset(&set);
   (void)sigprocmask(SIG_BLOCK, &set, &oset);
   if ((hashp->fp = mkstemp(namestr)) != -1) {
      (void)unlink(namestr);
      (void)fcntl(hashp->fp, F_SETFD, 1);
   }
   (void)sigprocmask(SIG_SETMASK, &oset, (sigset_t *)NULL);
   return (hashp->fp != -1 ? 0 : -1);
}

/*
 * We have to know that the key will fit, but the last entry on the page is
 * an overflow pair, so we need to shift things.
 */
static void
squeeze_key(sp, key, val)
   u_int16_t *sp;
   const DBT *key, *val;
{
   register char *p;
   u_int16_t free_space, n, off, pageno;

   p = (char *)sp;
   n = sp[0];
   free_space = FREESPACE(sp);
   off = OFFSET(sp);

   pageno = sp[n - 1];
   off -= key->size;
   sp[n - 1] = off;
   memmove(p + off, key->data, key->size);
   off -= val->size;
   sp[n] = off;
   memmove(p + off, val->data, val->size);
   sp[0] = n + 2;
   sp[n + 1] = pageno;
   sp[n + 2] = OVFLPAGE;
   FREESPACE(sp) = free_space - PAIRSIZE(key, val);
   OFFSET(sp) = off;
}

static u_int32_t *
fetch_bitmap(hashp, ndx)
   HTAB *hashp;
   int ndx;
{
   if (ndx >= hashp->nmaps)
      return (NULL);
   if ((hashp->mapp[ndx] = (u_int32_t *)malloc(hashp->BSIZE)) == NULL)
      return (NULL);
   if (__get_page(hashp,
       (char *)hashp->mapp[ndx], hashp->BITMAPS[ndx], 0, 1, 1)) {
      free(hashp->mapp[ndx]);
      return (NULL);
   }
   return (hashp->mapp[ndx]);
}

#ifdef DEBUG4
int
print_chain(addr)
   int addr;
{
   BUFHEAD *bufp;
   short *bp, oaddr;

   (void)fprintf(stderr, "%d ", addr);
   bufp = __get_buf(hashp, addr, NULL, 0);
   bp = (short *)bufp->page;
   while (bp[0] && ((bp[bp[0]] == OVFLPAGE) ||
      ((bp[0] > 2) && bp[2] < REAL_KEY))) {
      oaddr = bp[bp[0] - 1];
      (void)fprintf(stderr, "%d ", (int)oaddr);
      bufp = __get_buf(hashp, (int)oaddr, bufp, 0);
      bp = (short *)bufp->page;
   }
   (void)fprintf(stderr, "\n");
}
#endif