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dirhash.h

/*-
 * 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 1.5 2005/01/07 02:29:26 imp Exp $
 */

#ifndef _UFS_UFS_DIRHASH_H_
#define _UFS_UFS_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      (DIRECTSIZ(MAXNAMLEN + 1) / 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 {
      struct mtx dh_mtx;      /* protects all fields except dh_list */

      doff_t      **dh_hash;  /* the hash array (2-level) */
      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 */

      /* Free space statistics. XXX assumes DIRBLKSIZ is 512. */
      u_int8_t *dh_blkfree;   /* free DIRALIGN words in each dir block */
      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 ufsdirhash_list chain */

      /* Protected by ufsdirhash_mtx. */
      TAILQ_ENTRY(dirhash) dh_list; /* chain of all dirhashes */
};


/*
 * Dirhash functions.
 */
void  ufsdirhash_init(void);
void  ufsdirhash_uninit(void);
int   ufsdirhash_build(struct inode *);
doff_t      ufsdirhash_findfree(struct inode *, int, int *);
doff_t      ufsdirhash_enduseful(struct inode *);
int   ufsdirhash_lookup(struct inode *, char *, int, doff_t *, struct buf **,
          doff_t *);
void  ufsdirhash_newblk(struct inode *, doff_t);
void  ufsdirhash_add(struct inode *, struct direct *, doff_t);
void  ufsdirhash_remove(struct inode *, struct direct *, doff_t);
void  ufsdirhash_move(struct inode *, struct direct *, doff_t, doff_t);
void  ufsdirhash_dirtrunc(struct inode *, doff_t);
void  ufsdirhash_free(struct inode *);

void  ufsdirhash_checkblock(struct inode *, char *, doff_t);

#endif /* !_UFS_UFS_DIRHASH_H_ */

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