| 1 | /* |
| 2 | * Copyright (c) 2007 The DragonFly Project. All rights reserved. |
| 3 | * |
| 4 | * This code is derived from software contributed to The DragonFly Project |
| 5 | * by Matthew Dillon <dillon@backplane.com> |
| 6 | * |
| 7 | * Redistribution and use in source and binary forms, with or without |
| 8 | * modification, are permitted provided that the following conditions |
| 9 | * are met: |
| 10 | * |
| 11 | * 1. Redistributions of source code must retain the above copyright |
| 12 | * notice, this list of conditions and the following disclaimer. |
| 13 | * 2. Redistributions in binary form must reproduce the above copyright |
| 14 | * notice, this list of conditions and the following disclaimer in |
| 15 | * the documentation and/or other materials provided with the |
| 16 | * distribution. |
| 17 | * 3. Neither the name of The DragonFly Project nor the names of its |
| 18 | * contributors may be used to endorse or promote products derived |
| 19 | * from this software without specific, prior written permission. |
| 20 | * |
| 21 | * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 22 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 23 | * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| 24 | * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| 25 | * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| 26 | * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| 27 | * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; |
| 28 | * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED |
| 29 | * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, |
| 30 | * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT |
| 31 | * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 32 | * SUCH DAMAGE. |
| 33 | * |
| 34 | * $DragonFly: src/sys/vfs/hammer/hammer_btree.h,v 1.12 2008/02/10 09:51:01 dillon Exp $ |
| 35 | */ |
| 36 | |
| 37 | /* |
| 38 | * HAMMER B-Tree index |
| 39 | * |
| 40 | * HAMMER implements a modified B+Tree. B+Trees store records only |
| 41 | * at their leaves and HAMMER's modification is to adjust the internal |
| 42 | * elements so there is a boundary element on each side instead of sub-tree |
| 43 | * pointers. |
| 44 | * |
| 45 | * We just call our modified B+Tree a 'B-Tree' in HAMMER documentation to |
| 46 | * reduce confusion. |
| 47 | * |
| 48 | * A B-Tree internal node looks like this: |
| 49 | * |
| 50 | * B N N N N N N B <-- boundary and internal elements |
| 51 | * S S S S S S S <-- subtree pointers |
| 52 | * |
| 53 | * A B-Tree leaf node looks like this: |
| 54 | * |
| 55 | * L L L L L L L L <-- leaf elemenets |
| 56 | * (there is also a previous and next-leaf pointer) |
| 57 | * |
| 58 | * The recursion radix of an internal node is reduced by 1 relative to |
| 59 | * a normal B-Tree in order to accomodate the right-hand boundary. |
| 60 | * |
| 61 | * The big benefit to using a B-Tree with built-in bounds information is |
| 62 | * that it makes it possible to cache pointers into the middle of the tree |
| 63 | * and not have to start searches, insertions, OR deletions at the root node. |
| 64 | * The boundary elements allow searches to progress in a definitive direction |
| 65 | * from any point in the tree without revisting nodes. It is also possible |
| 66 | * to terminate searches early and make minor adjustments to the boundaries |
| 67 | * (within the confines of the parent's boundaries) on the fly. This greatly |
| 68 | * improves the efficiency of many operations, most especially record appends. |
| 69 | * |
| 70 | * HAMMER B-Trees are per-cluster. The global multi-cluster B-Tree is |
| 71 | * constructed by allowing internal nodes to link to the roots of other |
| 72 | * clusters. Fields in the cluster header then reference back to its |
| 73 | * parent and use the cluster generation number to detect stale linkages. |
| 74 | * |
| 75 | * The B-Tree balancing code can operate within a cluster or across the |
| 76 | * filesystem's ENTIRE B-Tree super-structure. A cluster's B-Tree root |
| 77 | * can be a leaf node in the worse case. A cluster is guarenteed to have |
| 78 | * sufficient free space to hold a single completely full leaf in the |
| 79 | * degenerate case. |
| 80 | * |
| 81 | * All of the structures below are on-disk structures. |
| 82 | */ |
| 83 | |
| 84 | /* |
| 85 | * Common base for all B-Tree element types (40 bytes) |
| 86 | * |
| 87 | * obj_type is set to the object type the record represents if an inode, |
| 88 | * directory entry, or an inter-cluster reference. A cluster range is |
| 89 | * special in that the B-Tree nodes represent a range within the B-Tree |
| 90 | * inclusive of rec_type field, so obj_type must be used to detect the |
| 91 | * cluster range entries. |
| 92 | * |
| 93 | * btype is only used by the elements making up an internal or leaf B-Tree |
| 94 | * node and applies to the node rather then to the key. This means that |
| 95 | * btype must be assigned/reassigned after any update to the base_elm making |
| 96 | * up a B-Tree element. |
| 97 | */ |
| 98 | struct hammer_base_elm { |
| 99 | int64_t obj_id; /* 00 object record is associated with */ |
| 100 | int64_t key; /* 08 indexing key (offset or namekey) */ |
| 101 | |
| 102 | hammer_tid_t create_tid; /* 10 transaction id for record creation */ |
| 103 | hammer_tid_t delete_tid; /* 18 transaction id for record update/del */ |
| 104 | |
| 105 | u_int16_t rec_type; /* 20 _RECTYPE_ */ |
| 106 | u_int8_t obj_type; /* 22 _OBJTYPE_ (restricted) */ |
| 107 | u_int8_t btype; /* 23 B-Tree element type */ |
| 108 | int32_t reserved07; /* 24 (future) */ |
| 109 | /* 28 */ |
| 110 | }; |
| 111 | |
| 112 | typedef struct hammer_base_elm *hammer_base_elm_t; |
| 113 | |
| 114 | /* |
| 115 | * Internal element (40 + 24 = 64 bytes). |
| 116 | * |
| 117 | * An internal element contains the left-hand boundary, right-hand boundary, |
| 118 | * and a recursion to another B-Tree node. |
| 119 | */ |
| 120 | struct hammer_btree_internal_elm { |
| 121 | struct hammer_base_elm base; |
| 122 | hammer_off_t unused00; |
| 123 | hammer_off_t subtree_offset; |
| 124 | int32_t unused02; |
| 125 | int32_t unused03; |
| 126 | }; |
| 127 | |
| 128 | /* |
| 129 | * Leaf B-Tree element (40 + 24 = 64 bytes). |
| 130 | * |
| 131 | * A leaf element. |
| 132 | */ |
| 133 | struct hammer_btree_leaf_elm { |
| 134 | struct hammer_base_elm base; |
| 135 | hammer_off_t rec_offset; |
| 136 | hammer_off_t data_offset; |
| 137 | int32_t data_len; |
| 138 | u_int32_t data_crc; |
| 139 | }; |
| 140 | |
| 141 | /* |
| 142 | * Rollup btree leaf element types - 64 byte structure |
| 143 | */ |
| 144 | union hammer_btree_elm { |
| 145 | struct hammer_base_elm base; |
| 146 | struct hammer_btree_leaf_elm leaf; |
| 147 | struct hammer_btree_internal_elm internal; |
| 148 | }; |
| 149 | |
| 150 | typedef union hammer_btree_elm *hammer_btree_elm_t; |
| 151 | |
| 152 | /* |
| 153 | * B-Tree node (normal or meta) (16x64 = 1K structure) |
| 154 | * |
| 155 | * Each node contains 15 elements. The last element for an internal node |
| 156 | * is the right-boundary so internal nodes have one fewer logical elements |
| 157 | * then leaf nodes. |
| 158 | * |
| 159 | * 'count' always refers to the number of elements and is non-inclusive of |
| 160 | * the right-hand boundary for an internal node. |
| 161 | * |
| 162 | * NOTE: The node head for an internal does not contain the subtype |
| 163 | * (The B-Tree node type for the nodes referenced by its elements). |
| 164 | * Instead, each element specifies the subtype (elm->base.subtype). |
| 165 | * This allows us to maintain an unbalanced B-Tree and to easily identify |
| 166 | * special inter-cluster link elements. |
| 167 | * |
| 168 | * NOTE: FUTURE EXPANSION: The reserved fields in hammer_node_ondisk are |
| 169 | * reserved for left/right leaf linkage fields, flags, and other future |
| 170 | * features. |
| 171 | */ |
| 172 | #define HAMMER_BTREE_LEAF_ELMS 15 |
| 173 | #define HAMMER_BTREE_INT_ELMS (HAMMER_BTREE_LEAF_ELMS - 1) |
| 174 | |
| 175 | /* |
| 176 | * It is safe to combine two adjacent nodes if the total number of elements |
| 177 | * is less then or equal to the *_FILL constant. |
| 178 | */ |
| 179 | #define HAMMER_BTREE_LEAF_FILL (HAMMER_BTREE_LEAF_ELMS - 3) |
| 180 | #define HAMMER_BTREE_INT_FILL (HAMMER_BTREE_INT_ELMS - 3) |
| 181 | |
| 182 | #define HAMMER_BTREE_TYPE_INTERNAL ((u_int8_t)'I') |
| 183 | #define HAMMER_BTREE_TYPE_LEAF ((u_int8_t)'L') |
| 184 | #define HAMMER_BTREE_TYPE_RECORD ((u_int8_t)'R') |
| 185 | |
| 186 | struct hammer_node_ondisk { |
| 187 | /* |
| 188 | * B-Tree node header (64 bytes) |
| 189 | */ |
| 190 | u_int32_t signature; |
| 191 | u_int32_t crc; |
| 192 | hammer_off_t parent; /* 0 if at root of cluster */ |
| 193 | int32_t count; |
| 194 | u_int8_t type; |
| 195 | u_int8_t reserved01; |
| 196 | u_int16_t reserved02; |
| 197 | hammer_off_t reserved03; /* future link_left */ |
| 198 | hammer_off_t reserved04; /* future link_right */ |
| 199 | hammer_off_t reserved05; |
| 200 | hammer_off_t reserved06; |
| 201 | hammer_off_t reserved07; |
| 202 | |
| 203 | /* |
| 204 | * Element array. Internal nodes have one less logical element |
| 205 | * (meaning: the same number of physical elements) in order to |
| 206 | * accomodate the right-hand boundary. The left-hand boundary |
| 207 | * is integrated into the first element. Leaf nodes have no |
| 208 | * boundary elements. |
| 209 | */ |
| 210 | union hammer_btree_elm elms[HAMMER_BTREE_LEAF_ELMS]; |
| 211 | }; |
| 212 | |
| 213 | typedef struct hammer_node_ondisk *hammer_node_ondisk_t; |
| 214 | |