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/* Directory name lookup caching
Copyright (C) 1996 Free Software Foundation, Inc.
Written by Michael I. Bushnell, p/BSG.
This file is part of the GNU Hurd.
The GNU Hurd is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2, or (at
your option) any later version.
The GNU Hurd is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111, USA. */
#include "priv.h"
#include <string.h>
/* Maximum number of names to cache at once */
#define MAXCACHE 256
/* Maximum length of file name we bother caching */
#define CACHE_NAME_LEN 100
/* Cache entry */
struct lookup_cache
{
int dir_cache_id, node_cache_id;
size_t len; /* strlen of name */
char name[CACHE_NAME_LEN];
};
/* The contents of the cache in no particular order */
static struct lookup_cache lookup_cache[MAXCACHE];
/* A rotating buffer of cache entries, maintaining an LRU
ordering of lookup_cache. */
static int cache_indexes[MAXCACHE];
/* The current live entries start at first_cache and run through to
last_cache. When the cache is full, first_cache == last_cache,
and these point at the lru element; lower indexes in cache_indexes
are successively less recently used. */
static int first_cache, last_cache;
static spin_lock_t cache_lock = SPIN_LOCK_INITIALIZER;
/* Buffer to hold statistics */
static struct
{
long pos_hits;
long neg_hits;
long miss;
long fetch_errors;
} statistics;
/* Node NP has just been found in DIR with NAME. If NP is null, that
means that this name has been confirmed as absent in the directory. */
void
diskfs_enter_lookup_cache (struct node *dir, struct node *np, char *name)
{
size_t len = strlen (name);
struct lookup_cache *lc;
if (len > CACHE_NAME_LEN - 1)
return;
spin_lock (&cache_lock);
/* Take first_cache + 1 and fill it with the new entry */
lc = &lookup_cache[cache_indexes[first_cache + 1]];
lc->dir_cache_id = dir->cache_id;
lc->node_cache_id = np->cache_id;
lc->len = len;
strcpy (lc->name, name);
/* Increment first_cache, and possibly last_cache too. */
if (last_cache == first_cache)
last_cache++;
first_cache++;
spin_unlock (&cache_lock);
}
/* Purge all references in the cache to NP as a node inside
directory DP. */
void
diskfs_purge_lookup_cache (struct node *dp, struct node *np)
{
int i;
spin_lock (&cache_lock);
for (i = 0; i < MAXCACHE; i++)
if (lookup_cache[i].len
&& lookup_cache[i].dir_cache_id == dp->cache_id
&& lookup_cache[i].node_cache_id == np->cache_id)
lookup_cache[i].len = 0;
spin_unlock (&cache_lock);
}
/* Scan the cache looking for NAME inside DIR. If we don't know
anything entry at all, then return 0. If the entry is confirmed to
not exist, then return -1. Otherwise, return NP for the entry, with
a newly allocated reference. */
struct node *
diskfs_check_lookup_cache (struct node *dir, char *name)
{
int i;
size_t len = strlen (name);
spin_lock (&cache_lock);
/* Maybe we really ought to look up in lru order...who knows. */
for (i = 0; i < MAXCACHE; i++)
if (lookup_cache[i].len == len
&& lookup_cache[i].dir_cache_id == dir->cache_id
&& lookup_cache[i].name[0] == name[0]
&& !strcmp (lookup_cache[i].name, name))
{
int id = lookup_cache[i].node_cache_id;
statistics.pos_hits++;
spin_unlock (&cache_lock);
if (id == dir->cache_id)
/* The cached node is the same as DIR. */
{
diskfs_nref (dir);
return dir;
}
else
{
struct node *np;
error_t err = diskfs_cached_lookup (id, &np);
return err ? 0 : np;
}
}
statistics.miss++;
spin_unlock (&cache_lock);
return 0;
}
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