1 /* $NetBSD: dirhash.h,v 1.9 2021/08/19 20:56:36 andvar Exp $ */ 2 3 /* 4 * Copyright (c) 2001 Ian Dowse. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 * 27 * $FreeBSD: src/sys/ufs/ufs/dirhash.h,v 1.2.2.2 2004/12/08 11:54:13 dwmalone Exp $ 28 */ 29 30 #ifndef _UFS_UFS_DIRHASH_H_ 31 #define _UFS_UFS_DIRHASH_H_ 32 33 /* 34 * For fast operations on large directories, we maintain a hash 35 * that maps the file name to the offset of the directory entry within 36 * the directory file. 37 * 38 * The hashing uses a dumb spillover to the next free slot on 39 * collisions, so we must keep the utilisation low to avoid 40 * long linear searches. Deleted entries that are not the last 41 * in a chain must be marked DIRHASH_DEL. 42 * 43 * We also maintain information about free space in each block 44 * to speed up creations. 45 */ 46 #define DIRHASH_EMPTY (-1) /* entry unused */ 47 #define DIRHASH_DEL (-2) /* deleted entry; may be part of chain */ 48 49 #define DIRALIGN 4 50 #define DH_NFSTATS (UFS_DIRECTSIZ(FFS_MAXNAMLEN + 1) / DIRALIGN) 51 /* max DIRALIGN words in a directory entry */ 52 53 /* 54 * Dirhash uses a score mechanism to achieve a hybrid between a 55 * least-recently-used and a least-often-used algorithm for entry 56 * recycling. The score is incremented when a directory is used, and 57 * decremented when the directory is a candidate for recycling. When 58 * the score reaches zero, the hash is recycled. Hashes are linked 59 * together on a TAILQ list, and hashes with higher scores filter 60 * towards the tail (most recently used) end of the list. 61 * 62 * New hash entries are given an initial score of DH_SCOREINIT and are 63 * placed at the most-recently-used end of the list. This helps a lot 64 * in the worst-case case scenario where every directory access is 65 * to a directory that is not hashed (i.e. the working set of hash 66 * candidates is much larger than the configured memory limit). In this 67 * case it limits the number of hash builds to 1/DH_SCOREINIT of the 68 * number of accesses. 69 */ 70 #define DH_SCOREINIT 8 /* initial dh_score when dirhash built */ 71 #define DH_SCOREMAX 64 /* max dh_score value */ 72 73 /* 74 * The main hash table has 2 levels. It is an array of pointers to 75 * blocks of DH_NBLKOFF offsets. 76 */ 77 #define DH_BLKOFFSHIFT 8 78 #define DH_NBLKOFF (1 << DH_BLKOFFSHIFT) 79 #define DH_BLKOFFMASK (DH_NBLKOFF - 1) 80 81 #define DH_ENTRY(dh, slot) \ 82 ((dh)->dh_hash[(slot) >> DH_BLKOFFSHIFT][(slot) & DH_BLKOFFMASK]) 83 84 struct dirhash { 85 kmutex_t dh_lock; /* protects all fields except dh_list */ 86 87 doff_t **dh_hash; /* the hash array (2-level) */ 88 size_t dh_hashsz; 89 int dh_narrays; /* number of entries in dh_hash */ 90 int dh_hlen; /* total slots in the 2-level hash array */ 91 int dh_hused; /* entries in use */ 92 93 u_int8_t *dh_blkfree; /* free DIRALIGN words in each dir block */ 94 size_t dh_blkfreesz; 95 int dh_nblk; /* size of dh_blkfree array */ 96 int dh_dirblks; /* number of DIRBLKSIZ blocks in dir */ 97 int dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */ 98 99 int dh_seqopt; /* sequential access optimisation enabled */ 100 doff_t dh_seqoff; /* sequential access optimisation offset */ 101 102 int dh_score; /* access count for this dirhash */ 103 104 int dh_onlist; /* true if on the ufsdirhash_list chain */ 105 106 /* Protected by ufsdirhash_lock. */ 107 TAILQ_ENTRY(dirhash) dh_list; /* chain of all dirhashes */ 108 }; 109 110 111 /* 112 * Dirhash functions. 113 */ 114 int ufsdirhash_build(struct inode *); 115 doff_t ufsdirhash_findfree(struct inode *, int, int *); 116 doff_t ufsdirhash_enduseful(struct inode *); 117 int ufsdirhash_lookup(struct inode *, const char *, int, doff_t *, 118 struct buf **, doff_t *); 119 void ufsdirhash_newblk(struct inode *, doff_t); 120 void ufsdirhash_add(struct inode *, struct direct *, doff_t); 121 void ufsdirhash_remove(struct inode *, struct direct *, doff_t); 122 void ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t); 123 void ufsdirhash_dirtrunc(struct inode *, doff_t); 124 void ufsdirhash_free(struct inode *); 125 void ufsdirhash_checkblock(struct inode *, char *, doff_t); 126 void ufsdirhash_init(void); 127 void ufsdirhash_done(void); 128 129 #endif /* !_UFS_UFS_DIRHASH_H_ */ 130