## root/libdb/bt_overflow.c

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## DEFINITIONS

This source file includes following definitions.

1. __ovfl_get
2. __ovfl_put
3. __ovfl_delete

    /*-
     * 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
     * Mike Olson.
     *
     * 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. 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[] = "@(#)bt_overflow.c       8.5 (Berkeley) 7/16/94";
    #endif /* LIBC_SCCS and not lint */

    #ifdef HAVE_CONFIG_H
    #include <config.h>
    #endif
    #include <stdio.h>
    #ifdef STDC_HEADERS
    #include <stdlib.h>
    #endif
    #ifdef HAVE_STRING_H
    #include <string.h>
    #else
    #include <strings.h>
    #endif

    #include "db.h"
    #include "btree.h"

    /*
     * Big key/data code.
     *
     * Big key and data entries are stored on linked lists of pages.  The initial
     * reference is byte string stored with the key or data and is the page number
     * and size.  The actual record is stored in a chain of pages linked by the
     * nextpg field of the PAGE header.
     *
     * The first page of the chain has a special property.  If the record is used
     * by an internal page, it cannot be deleted and the P_PRESERVE bit will be set
     * in the header.
     *
     * XXX
     * A single DBT is written to each chain, so a lot of space on the last page
     * is wasted.  This is a fairly major bug for some data sets.
     */

    /*
     * __OVFL_GET -- Get an overflow key/data item.
     *
     * Parameters:
     *      t:      tree
     *      p:      pointer to { pgno_t, u_int32_t }
     *      buf:    storage address
     *      bufsz:  storage size
     *
     * Returns:
     *      RET_ERROR, RET_SUCCESS
     */
    int
    __ovfl_get(t, p, ssz, buf, bufsz)
            BTREE *t;
            void *p;
            size_t *ssz;
            void **buf;
            size_t *bufsz;
    {
            PAGE *h;
            pgno_t pg;
            size_t nb, plen;
            u_int32_t sz;

            memmove(&pg, p, sizeof(pgno_t));
            memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));
            *ssz = sz;

    #ifdef DEBUG
            if (pg == P_INVALID || sz == 0)
                    abort();
    #endif
            /* Make the buffer bigger as necessary. */
            if (*bufsz < sz) {
                    *buf = (char *)(*buf == NULL ? malloc(sz) : realloc(*buf, sz));
                    if (*buf == NULL)
                            return (RET_ERROR);
                    *bufsz = sz;
            }

            /*
             * Step through the linked list of pages, copying the data on each one
             * into the buffer.  Never copy more than the data's length.
             */
            plen = t->bt_psize - BTDATAOFF;
            for (p = *buf;; p = (char *)p + nb, pg = h->nextpg) {
                    if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                            return (RET_ERROR);

                    nb = MIN(sz, plen);
                    memmove(p, (char *)h + BTDATAOFF, nb);
                    mpool_put(t->bt_mp, h, 0);

                    if ((sz -= nb) == 0)
                            break;
            }
            return (RET_SUCCESS);
    }

    /*
     * __OVFL_PUT -- Store an overflow key/data item.
     *
     * Parameters:
     *      t:      tree
     *      data:   DBT to store
     *      pgno:   storage page number
     *
     * Returns:
     *      RET_ERROR, RET_SUCCESS
     */
    int
    __ovfl_put(t, dbt, pg)
            BTREE *t;
            const DBT *dbt;
            pgno_t *pg;
    {
            PAGE *h, *last;
            void *p;
            pgno_t npg;
            size_t nb, plen;
            u_int32_t sz;

            /*
             * Allocate pages and copy the key/data record into them.  Store the
             * number of the first page in the chain.
             */
            plen = t->bt_psize - BTDATAOFF;
            for (last = NULL, p = dbt->data, sz = dbt->size;;
                p = (char *)p + plen, last = h) {
                    if ((h = __bt_new(t, &npg)) == NULL)
                            return (RET_ERROR);

                    h->pgno = npg;
                    h->nextpg = h->prevpg = P_INVALID;
                    h->flags = P_OVERFLOW;
                    h->lower = h->upper = 0;

                    nb = MIN(sz, plen);
                    memmove((char *)h + BTDATAOFF, p, nb);

                    if (last) {
                            last->nextpg = h->pgno;
                            mpool_put(t->bt_mp, last, MPOOL_DIRTY);
                    } else
                            *pg = h->pgno;

                    if ((sz -= nb) == 0) {
                            mpool_put(t->bt_mp, h, MPOOL_DIRTY);
                            break;
                    }
            }
            return (RET_SUCCESS);
    }

    /*
     * __OVFL_DELETE -- Delete an overflow chain.
     *
     * Parameters:
     *      t:      tree
     *      p:      pointer to { pgno_t, u_int32_t }
     *
     * Returns:
     *      RET_ERROR, RET_SUCCESS
     */
    int
    __ovfl_delete(t, p)
            BTREE *t;
            void *p;
    {
            PAGE *h;
            pgno_t pg;
            size_t plen;
            u_int32_t sz;

            memmove(&pg, p, sizeof(pgno_t));
            memmove(&sz, (char *)p + sizeof(pgno_t), sizeof(u_int32_t));

    #ifdef DEBUG
            if (pg == P_INVALID || sz == 0)
                    abort();
    #endif
            if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                    return (RET_ERROR);

            /* Don't delete chains used by internal pages. */
            if (h->flags & P_PRESERVE) {
                    mpool_put(t->bt_mp, h, 0);
                    return (RET_SUCCESS);
            }

            /* Step through the chain, calling the free routine for each page. */
            for (plen = t->bt_psize - BTDATAOFF;; sz -= plen) {
                    pg = h->nextpg;
                    __bt_free(t, h);
                    if (sz <= plen)
                            break;
                    if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL)
                            return (RET_ERROR);
            }
            return (RET_SUCCESS);
    }

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