lib/libc/db/btree/updutils.c

/*-
 * Copyright (c) 1990 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. 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[] = "@(#)updutils.c  5.2 (Berkeley) 2/22/91";
#endif /* LIBC_SCCS and not lint */

#include <sys/types.h>
#include <db.h>
#include <stdlib.h>
#include <string.h>
#include "btree.h"

/*
 *  _BT_FIXSCAN -- Adjust a scan to cope with a change in tree structure.
 *
 *      If the user has an active scan on the database, and we delete an
 *      item from the page the cursor is pointing at, we need to figure
 *      out what to do about it.  Basically, the solution is to point
 *      "between" keys in the tree, using the CRSR_BEFORE flag.  The
 *      requirement is that the user should not miss any data in the
 *      tree during a scan, just because he happened to do some deletions
 *      or insertions while it was active.
 *
 *      In order to guarantee that the scan progresses properly, we need
 *      to save the key of any deleted item we were pointing at, so that
 *      we can check later insertions against it.
 *
 *      Parameters:
 *              t -- tree to adjust
 *              index -- index of item at which change was made
 *              newd -- new datum (for insertions only)
 *              op -- operation (DELETE or INSERT) causing change
 *
 *      Returns:
 *              RET_SUCCESS, RET_ERROR (errno is set).
 *
 *      Side Effects:
 *              None.
 */

int
_bt_fixscan(t, index, newd, op)
        BTREE_P t;
        index_t index;
        DATUM *newd;
        int op;
{
        CURSOR *c;
        DATUM *d;

        c = &(t->bt_cursor);

        if (op == DELETE) {
                if (index < c->c_index)
                        c->c_index--;
                else if (index == c->c_index) {
                        if (!(c->c_flags & CRSR_BEFORE)) {
                                if (_bt_crsrkey(t) == RET_ERROR)
                                        return (RET_ERROR);
                                c->c_flags |= CRSR_BEFORE;
                        }
                }
        } else {
                /*
                 *  If we previously deleted the object at this location,
                 *  and now we're inserting a new one, we need to do the
                 *  right thing -- the cursor should come either before
                 *  or after the new item, depending on the key that was
                 *  here, and the new one.
                 */

                if (c->c_flags & CRSR_BEFORE) {
                        if (index <= c->c_index) {
                                char *tmp;
                                int itmp;
                                pgno_t chain;
                                int r;

                                d = (DATUM *) GETDATUM(t->bt_curpage, index);
                                if (d->d_flags & D_BIGKEY) {
                                        bcopy(&(newd->d_bytes[0]),
                                              (char *) &chain,
                                              sizeof(chain));
                                        if (_bt_getbig(t, chain, &tmp, &itmp)
                                             == RET_ERROR)
                                                return (RET_ERROR);
                                } else
                                        tmp = &(newd->d_bytes[0]);

                                r = (*(t->bt_compare))(tmp, c->c_key);
                                if (r < 0)
                                        c->c_index++;

                                if (d->d_flags & D_BIGKEY)
                                        (void) free (tmp);
                        }
                } else if (index <= c->c_index)
                        c->c_index++;
        }
        return (RET_SUCCESS);
}

/*
 *  _BT_CRSRKEY -- Save a copy of the key of the record that the cursor
 *                 is pointing to.  The record is about to be deleted.
 *
 *      Parameters:
 *              t -- btree
 *
 *      Returns:
 *              RET_SUCCESS, RET_ERROR.
 *
 *      Side Effects:
 *              Allocates memory for the copy which should be released when
 *              it is no longer needed.
 */

int
_bt_crsrkey(t)
        BTREE_P t;
{
        CURSOR *c;
        DATUM *d;
        pgno_t pgno;
        int ignore;

        c = &(t->bt_cursor);
        d = (DATUM *) GETDATUM(t->bt_curpage, c->c_index);

        if (d->d_flags & D_BIGKEY) {
                bcopy(&(d->d_bytes[0]), (char *) &pgno, sizeof(pgno));
                return (_bt_getbig(t, pgno, &(c->c_key), &ignore));
        } else {
                if ((c->c_key = (char *) malloc(d->d_ksize)) == (char *) NULL)
                        return (RET_ERROR);

                bcopy(&(d->d_bytes[0]), c->c_key, (size_t) (d->d_ksize));
        }
        return (RET_SUCCESS);
}