2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2001 Ian Dowse. All rights reserved.
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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
30 #ifndef _UFS_UFS_DIRHASH_H_
31 #define _UFS_UFS_DIRHASH_H_
33 #include <sys/_lock.h>
37 * For fast operations on large directories, we maintain a hash
38 * that maps the file name to the offset of the directory entry within
41 * The hashing uses a dumb spillover to the next free slot on
42 * collisions, so we must keep the utilisation low to avoid
43 * long linear searches. Deleted entries that are not the last
44 * in a chain must be marked DIRHASH_DEL.
46 * We also maintain information about free space in each block
47 * to speed up creations.
49 #define DIRHASH_EMPTY (-1) /* entry unused */
50 #define DIRHASH_DEL (-2) /* deleted entry; may be part of chain */
53 #define DH_NFSTATS (DIRECTSIZ(UFS_MAXNAMLEN + 1) / DIRALIGN)
54 /* max DIRALIGN words in a directory entry */
57 * Dirhash uses a score mechanism to achieve a hybrid between a
58 * least-recently-used and a least-often-used algorithm for entry
59 * recycling. The score is incremented when a directory is used, and
60 * decremented when the directory is a candidate for recycling. When
61 * the score reaches zero, the hash is recycled. Hashes are linked
62 * together on a TAILQ list, and hashes with higher scores filter
63 * towards the tail (most recently used) end of the list.
65 * New hash entries are given an initial score of DH_SCOREINIT and are
66 * placed at the most-recently-used end of the list. This helps a lot
67 * in the worst-case case scenario where every directory access is
68 * to a directory that is not hashed (i.e. the working set of hash
69 * candidates is much larger than the configured memory limit). In this
70 * case it limits the number of hash builds to 1/DH_SCOREINIT of the
73 #define DH_SCOREINIT 8 /* initial dh_score when dirhash built */
74 #define DH_SCOREMAX 64 /* max dh_score value */
77 * The main hash table has 2 levels. It is an array of pointers to
78 * blocks of DH_NBLKOFF offsets.
80 #define DH_BLKOFFSHIFT 8
81 #define DH_NBLKOFF (1 << DH_BLKOFFSHIFT)
82 #define DH_BLKOFFMASK (DH_NBLKOFF - 1)
84 #define DH_ENTRY(dh, slot) \
85 ((dh)->dh_hash[(slot) >> DH_BLKOFFSHIFT][(slot) & DH_BLKOFFMASK])
88 struct sx dh_lock; /* protects all fields except list & score */
91 doff_t **dh_hash; /* the hash array (2-level) */
92 int dh_narrays; /* number of entries in dh_hash */
93 int dh_hlen; /* total slots in the 2-level hash array */
94 int dh_hused; /* entries in use */
95 int dh_memreq; /* Memory used. */
97 /* Free space statistics. XXX assumes DIRBLKSIZ is 512. */
98 u_int8_t *dh_blkfree; /* free DIRALIGN words in each dir block */
99 int dh_nblk; /* size of dh_blkfree array */
100 int dh_dirblks; /* number of DIRBLKSIZ blocks in dir */
101 int dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */
103 doff_t dh_seqoff; /* sequential access optimisation offset */
105 int dh_score; /* access count for this dirhash */
107 int dh_onlist; /* true if on the ufsdirhash_list chain */
109 time_t dh_lastused; /* time the dirhash was last read or written*/
111 /* Protected by ufsdirhash_mtx. */
112 TAILQ_ENTRY(dirhash) dh_list; /* chain of all dirhashes */
118 void ufsdirhash_init(void);
119 void ufsdirhash_uninit(void);
120 int ufsdirhash_build(struct inode *);
121 doff_t ufsdirhash_findfree(struct inode *, int, int *);
122 doff_t ufsdirhash_enduseful(struct inode *);
123 int ufsdirhash_lookup(struct inode *, char *, int, doff_t *, struct buf **,
125 void ufsdirhash_newblk(struct inode *, doff_t);
126 void ufsdirhash_add(struct inode *, struct direct *, doff_t);
127 void ufsdirhash_remove(struct inode *, struct direct *, doff_t);
128 void ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t);
129 void ufsdirhash_dirtrunc(struct inode *, doff_t);
130 void ufsdirhash_free(struct inode *);
132 void ufsdirhash_checkblock(struct inode *, char *, doff_t);
134 #endif /* !_UFS_UFS_DIRHASH_H_ */