Net2/usr/src/lib/libc/db/btree/delete.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[] = "@(#)delete.c 5.2 (Berkeley) 2/22/91";
#endif /* LIBC_SCCS and not lint */
#include <sys/types.h>
#include <db.h>
#include <errno.h>
#include <string.h>
#include "btree.h"
/*
* _BT_CRSRDEL -- Delete the item pointed to by the cursor.
*
* This routine deletes the item most recently returned by a scan
* through the tree. Since it only makes sense to delete the current
* record once, we make sure that we don't try to delete twice without
* advancing the scan.
*
* Parameters:
* t -- tree in which to do deletion
*
* Returns:
* RET_SUCCESS, RET_ERROR.
*
* Side Effects:
* The call to _bt_delone marks the cursor, so we can tell that
* the current record has been deleted.
*/
int
_bt_crsrdel(t)
BTREE_P t;
{
CURSOR *c;
c = &(t->bt_cursor);
/* a cursor must exist, and can't have deleted the current key yet */
if (!(t->bt_flags & BTF_SEQINIT) || (c->c_flags & CRSR_BEFORE)) {
errno = EINVAL;
return (RET_ERROR);
}
if (_bt_getpage(t, c->c_pgno) == RET_ERROR)
return (RET_ERROR);
if (c->c_index >= NEXTINDEX(t->bt_curpage)) {
errno = EINVAL;
return (RET_ERROR);
}
return (_bt_delone(t, c->c_index));
}
/*
* _BT_DELONE -- Delete a single entry from a btree.
*
* This routine physically removes a btree entry from a leaf page.
* IDATUM items are *never* removed from internal nodes, regardless
* of whether the entries that originally caused them to be added
* are removed from the tree or not. In addition, pages made empty
* by element deletion are not actually reclaimed. They are,
* however, made available for reuse.
*
* To delete an item from a page, we pack the remaining items at
* the end of the page, overwriting the deleted item's entry. We
* move the line pointers backward on the page, overwriting the
* original item's line pointer. This guarantees that the space in
* the middle of the page is free -- a property that our insertion
* strategy relies on.
*
* This routine doesn't reclaim pages all of whose entries have
* been deleted. These pages are available for reuse, however.
* If an item is deleted that was too big to fit on a page, then
* the blocks that it occupies are put on a free list for reuse.
*
* Parameters:
* t -- btree from which to delete item
* index -- index of entry on current page to delete
*
* Returns:
* RET_SUCCESS, RET_ERROR.
*
* Side Effects:
* Physically changes page layout, adjusts internal page
* state to reflect the deletion of the item, and updates
* the list of free pages for this tree.
*/
int
_bt_delone(t, index)
BTREE_P t;
index_t index;
{
char *src, *dest;
int nbytes, nmoved;
index_t off;
index_t top;
index_t i;
pgno_t chain;
BTHEADER *h;
CURSOR *c;
DATUM *d;
/* deletion may confuse an active scan. fix it. */
c = &(t->bt_cursor);
if (t->bt_flags & BTF_SEQINIT && t->bt_curpage->h_pgno == c->c_pgno)
if (_bt_fixscan(t, index, (DATUM *) NULL, DELETE) == RET_ERROR)
return (RET_ERROR);
h = t->bt_curpage;
off = h->h_linp[index];
d = (DATUM *) GETDATUM(h, index);
/* if this is a big item, reclaim the space it occupies */
if (d->d_flags & D_BIGKEY) {
bcopy(&(d->d_bytes[0]),
(char *) &chain,
sizeof(chain));
if (_bt_delindir(t, chain) == RET_ERROR)
return (RET_ERROR);
h = t->bt_curpage;
d = (DATUM *) GETDATUM(h, index);
}
if (d->d_flags & D_BIGDATA) {
bcopy(&(d->d_bytes[d->d_ksize]),
(char *) &chain,
sizeof(chain));
if (_bt_delindir(t, chain) == RET_ERROR)
return (RET_ERROR);
h = t->bt_curpage;
d = (DATUM *) GETDATUM(h, index);
}
/* move the data down on the page */
nbytes = d->d_ksize + d->d_dsize
+ (sizeof(DATUM) - sizeof(char));
nbytes = LONGALIGN(nbytes);
src = ((char *) h) + h->h_upper;
dest = src + nbytes;
nmoved = (int) (((char *) d) - src);
(void) bcopy(src, dest, nmoved);
/* next move the line pointers up */
src = (char *) &(h->h_linp[index + 1]);
dest = (char *) &(h->h_linp[index]);
nmoved = (int) (((char *) &(h->h_linp[NEXTINDEX(h)])) - src);
(void) bcopy(src, dest, nmoved);
/* remember that we freed up some space */
h->h_upper += nbytes;
h->h_lower -= sizeof(index_t);
/* adjust offsets in line pointers affected by moving the data */
top = NEXTINDEX(h);
for (i = 0; i < top; i++) {
if (h->h_linp[i] < off)
h->h_linp[i] += nbytes;
}
/* it's gone */
h->h_flags |= F_DIRTY;
return (RET_SUCCESS);
}