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/* $NetBSD: ulfs_dirhash.h,v 1.8 2015/09/21 01:24:23 dholland Exp $ */
/* from NetBSD: dirhash.h,v 1.6 2008/06/04 11:33:19 ad Exp */
/*
* Copyright (c) 2001 Ian Dowse. All rights reserved.
*
* 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.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
*
* $FreeBSD: src/sys/ufs/ufs/dirhash.h,v 1.2.2.2 2004/12/08 11:54:13 dwmalone Exp $
*/
#ifndef _UFS_LFS_ULFS_DIRHASH_H_
#define _UFS_LFS_ULFS_DIRHASH_H_
/*
* For fast operations on large directories, we maintain a hash
* that maps the file name to the offset of the directory entry within
* the directory file.
*
* The hashing uses a dumb spillover to the next free slot on
* collisions, so we must keep the utilisation low to avoid
* long linear searches. Deleted entries that are not the last
* in a chain must be marked DIRHASH_DEL.
*
* We also maintain information about free space in each block
* to speed up creations.
*/
#define DIRHASH_EMPTY (-1) /* entry unused */
#define DIRHASH_DEL (-2) /* deleted entry; may be part of chain */
#define DIRALIGN 4
#define DH_NFSTATS (LFS_MAXDIRENTRYSIZE / DIRALIGN)
/* max DIRALIGN words in a directory entry */
/*
* Dirhash uses a score mechanism to achieve a hybrid between a
* least-recently-used and a least-often-used algorithm for entry
* recycling. The score is incremented when a directory is used, and
* decremented when the directory is a candidate for recycling. When
* the score reaches zero, the hash is recycled. Hashes are linked
* together on a TAILQ list, and hashes with higher scores filter
* towards the tail (most recently used) end of the list.
*
* New hash entries are given an inital score of DH_SCOREINIT and are
* placed at the most-recently-used end of the list. This helps a lot
* in the worst-case case scenario where every directory access is
* to a directory that is not hashed (i.e. the working set of hash
* candidates is much larger than the configured memry limit). In this
* case it limits the number of hash builds to 1/DH_SCOREINIT of the
* number of accesses.
*/
#define DH_SCOREINIT 8 /* initial dh_score when dirhash built */
#define DH_SCOREMAX 64 /* max dh_score value */
/*
* The main hash table has 2 levels. It is an array of pointers to
* blocks of DH_NBLKOFF offsets.
*/
#define DH_BLKOFFSHIFT 8
#define DH_NBLKOFF (1 << DH_BLKOFFSHIFT)
#define DH_BLKOFFMASK (DH_NBLKOFF - 1)
#define DH_ENTRY(dh, slot) \
((dh)->dh_hash[(slot) >> DH_BLKOFFSHIFT][(slot) & DH_BLKOFFMASK])
struct dirhash {
kmutex_t dh_lock; /* protects all fields except dh_list */
doff_t **dh_hash; /* the hash array (2-level) */
size_t dh_hashsz;
int dh_narrays; /* number of entries in dh_hash */
int dh_hlen; /* total slots in the 2-level hash array */
int dh_hused; /* entries in use */
u_int8_t *dh_blkfree; /* free DIRALIGN words in each dir block */
size_t dh_blkfreesz;
int dh_nblk; /* size of dh_blkfree array */
int dh_dirblks; /* number of DIRBLKSIZ blocks in dir */
int dh_firstfree[DH_NFSTATS + 1]; /* first blk with N words free */
int dh_seqopt; /* sequential access optimisation enabled */
doff_t dh_seqoff; /* sequential access optimisation offset */
int dh_score; /* access count for this dirhash */
int dh_onlist; /* true if on the ulfsdirhash_list chain */
/* Protected by ulfsdirhash_lock. */
TAILQ_ENTRY(dirhash) dh_list; /* chain of all dirhashes */
};
/*
* Dirhash functions.
*/
int ulfsdirhash_build(struct inode *);
doff_t ulfsdirhash_findfree(struct inode *, int, int *);
doff_t ulfsdirhash_enduseful(struct inode *);
int ulfsdirhash_lookup(struct inode *, const char *, int, doff_t *,
struct buf **, doff_t *);
void ulfsdirhash_newblk(struct inode *, doff_t);
void ulfsdirhash_add(struct inode *, LFS_DIRHEADER *, doff_t);
void ulfsdirhash_remove(struct inode *, LFS_DIRHEADER *, doff_t);
void ulfsdirhash_move(struct inode *, LFS_DIRHEADER *, doff_t, doff_t);
void ulfsdirhash_dirtrunc(struct inode *, doff_t);
void ulfsdirhash_free(struct inode *);
void ulfsdirhash_checkblock(struct inode *, char *, doff_t);
void ulfsdirhash_init(void);
void ulfsdirhash_done(void);
#endif /* !_UFS_LFS_ULFS_DIRHASH_H_ */
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