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