1 /* $NetBSD: bt_get.c,v 1.6 1995/02/27 13:20:22 cgd Exp $ */ 2 3 /*- 4 * Copyright (c) 1990, 1993 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code is derived from software contributed to Berkeley by 8 * Mike Olson. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 */ 38 39 #if defined(LIBC_SCCS) && !defined(lint) 40 #if 0 41 static char sccsid[] = "@(#)bt_get.c 8.2 (Berkeley) 9/7/93"; 42 #else 43 static char rcsid[] = "$NetBSD: bt_get.c,v 1.6 1995/02/27 13:20:22 cgd Exp $"; 44 #endif 45 #endif /* LIBC_SCCS and not lint */ 46 47 #include <sys/types.h> 48 49 #include <errno.h> 50 #include <stddef.h> 51 #include <stdio.h> 52 53 #include <db.h> 54 #include "btree.h" 55 56 /* 57 * __BT_GET -- Get a record from the btree. 58 * 59 * Parameters: 60 * dbp: pointer to access method 61 * key: key to find 62 * data: data to return 63 * flag: currently unused 64 * 65 * Returns: 66 * RET_ERROR, RET_SUCCESS and RET_SPECIAL if the key not found. 67 */ 68 int 69 __bt_get(dbp, key, data, flags) 70 const DB *dbp; 71 const DBT *key; 72 DBT *data; 73 u_int flags; 74 { 75 BTREE *t; 76 EPG *e; 77 int exact, status; 78 79 t = dbp->internal; 80 81 /* Toss any page pinned across calls. */ 82 if (t->bt_pinned != NULL) { 83 mpool_put(t->bt_mp, t->bt_pinned, 0); 84 t->bt_pinned = NULL; 85 } 86 87 /* Get currently doesn't take any flags. */ 88 if (flags) { 89 errno = EINVAL; 90 return (RET_ERROR); 91 } 92 93 if ((e = __bt_search(t, key, &exact)) == NULL) 94 return (RET_ERROR); 95 if (!exact) { 96 mpool_put(t->bt_mp, e->page, 0); 97 return (RET_SPECIAL); 98 } 99 100 /* 101 * A special case is if we found the record but it's flagged for 102 * deletion. In this case, we want to find another record with the 103 * same key, if it exists. Rather than look around the tree we call 104 * __bt_first and have it redo the search, as __bt_first will not 105 * return keys marked for deletion. Slow, but should never happen. 106 */ 107 if (ISSET(t, B_DELCRSR) && e->page->pgno == t->bt_bcursor.pgno && 108 e->index == t->bt_bcursor.index) { 109 mpool_put(t->bt_mp, e->page, 0); 110 if ((e = __bt_first(t, key, &exact)) == NULL) 111 return (RET_ERROR); 112 if (!exact) 113 return (RET_SPECIAL); 114 } 115 116 status = __bt_ret(t, e, NULL, data); 117 /* 118 * If the user is doing concurrent access, we copied the 119 * key/data, toss the page. 120 */ 121 if (ISSET(t, B_DB_LOCK)) 122 mpool_put(t->bt_mp, e->page, 0); 123 else 124 t->bt_pinned = e->page; 125 return (status); 126 } 127 128 /* 129 * __BT_FIRST -- Find the first entry. 130 * 131 * Parameters: 132 * t: the tree 133 * key: the key 134 * 135 * Returns: 136 * The first entry in the tree greater than or equal to key. 137 */ 138 EPG * 139 __bt_first(t, key, exactp) 140 BTREE *t; 141 const DBT *key; 142 int *exactp; 143 { 144 register PAGE *h; 145 register EPG *e; 146 EPG save; 147 pgno_t cpgno, pg; 148 indx_t cindex; 149 int found; 150 151 /* 152 * Find any matching record; __bt_search pins the page. Only exact 153 * matches are tricky, otherwise just return the location of the key 154 * if it were to be inserted into the tree. 155 */ 156 if ((e = __bt_search(t, key, exactp)) == NULL) 157 return (NULL); 158 if (!*exactp) 159 return (e); 160 161 if (ISSET(t, B_DELCRSR)) { 162 cpgno = t->bt_bcursor.pgno; 163 cindex = t->bt_bcursor.index; 164 } else { 165 cpgno = P_INVALID; 166 cindex = 0; /* GCC thinks it's uninitialized. */ 167 } 168 169 /* 170 * Walk backwards, skipping empty pages, as long as the entry matches 171 * and there are keys left in the tree. Save a copy of each match in 172 * case we go too far. A special case is that we don't return a match 173 * on records that the cursor references that have already been flagged 174 * for deletion. 175 */ 176 save = *e; 177 h = e->page; 178 found = 0; 179 do { 180 if (cpgno != h->pgno || cindex != e->index) { 181 if (save.page->pgno != e->page->pgno) { 182 mpool_put(t->bt_mp, save.page, 0); 183 save = *e; 184 } else 185 save.index = e->index; 186 found = 1; 187 } 188 /* 189 * Make a special effort not to unpin the page the last (or 190 * original) match was on, but also make sure it's unpinned 191 * if an error occurs. 192 */ 193 while (e->index == 0) { 194 if (h->prevpg == P_INVALID) 195 goto done1; 196 if (h->pgno != save.page->pgno) 197 mpool_put(t->bt_mp, h, 0); 198 if ((h = mpool_get(t->bt_mp, h->prevpg, 0)) == NULL) { 199 if (h->pgno == save.page->pgno) 200 mpool_put(t->bt_mp, save.page, 0); 201 return (NULL); 202 } 203 e->page = h; 204 e->index = NEXTINDEX(h); 205 } 206 --e->index; 207 } while (__bt_cmp(t, key, e) == 0); 208 209 /* 210 * Reach here with the last page that was looked at pinned, which may 211 * or may not be the same as the last (or original) match page. If 212 * it's not useful, release it. 213 */ 214 done1: if (h->pgno != save.page->pgno) 215 mpool_put(t->bt_mp, h, 0); 216 217 /* 218 * If still haven't found a record, the only possibility left is the 219 * next one. Move forward one slot, skipping empty pages and check. 220 */ 221 if (!found) { 222 h = save.page; 223 if (++save.index == NEXTINDEX(h)) { 224 do { 225 pg = h->nextpg; 226 mpool_put(t->bt_mp, h, 0); 227 if (pg == P_INVALID) { 228 *exactp = 0; 229 return (e); 230 } 231 if ((h = mpool_get(t->bt_mp, pg, 0)) == NULL) 232 return (NULL); 233 } while ((save.index = NEXTINDEX(h)) == 0); 234 save.page = h; 235 } 236 if (__bt_cmp(t, key, &save) != 0) { 237 *exactp = 0; 238 return (e); 239 } 240 } 241 *e = save; 242 *exactp = 1; 243 return (e); 244 } 245