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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
/* Current number of names cached */
static int cache_cur;
/* Cache entry */
struct lookup_cache
{
struct lookup_cache *next, *prev;
/* These do not hold references; special code exists to call
purge routines when the nodes lose refs. */
struct node *dp; /* directory */
struct node *np; /* node */
/* strlen of name member */
size_t namelen;
char name[0];
};
/* Cache itself */
static struct lookup_cache *lookup_cache_head, *lookup_cache_tail;
/* Buffer to hold statistics */
static struct
{
long pos_hits;
long neg_hits;
long miss;
} 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_cache (struct node *dir, struct node *np, char *name)
{
struct lookup_cache *lc, *tmp = 0;
size_t len = strlen (name) + 1;
lc = malloc (sizeof (struct lookup_cache) + len);
lc->dp = dir;
lc->np = np;
lc->namelen = len - 1;
bcopy (name, lc->name, len);
spin_lock (&diskfs_node_refcnt_lock);
if (cache_cur == MAXCACHE)
{
/* Free the entry at the tail */
tmp = lookup_cache_tail;
lookup_cache_tail = lookup_cache_tail->prev;
if (lookup_cache_tail)
lookup_cache_tail->next = 0;
else
lookup_cache_head = 0;
}
else
cache_cur++;
/* Add the new entry at the front */
lc->next = lookup_cache_head;
lc->prev = 0;
if (lc->next)
lc->next->prev = lc;
lookup_cache_head = lc;
if (!lc->next)
lookup_cache_tail = lc;
spin_unlock (&diskfs_node_refcnt_lock);
if (tmp)
free (tmp);
}
/* Purge all references in the cache to NP as a node inside
directory DP. */
void
diskfs_purge_cache (struct node *dp, struct node *np)
{
struct lookup_cache *lc, *nxt;
spin_lock (&diskfs_node_refcnt_lock);
for (lc = lookup_cache_head; lc; lc = nxt)
if (lc->np == np && lc->dp == dp)
{
if (lc->prev)
lc->prev->next = lc->next;
if (lc->next)
lc->next->prev = lc->prev;
nxt = lc->next;
free (lc);
}
else
nxt = lc->next;
spin_unlock (&diskfs_node_refcnt_lock);
}
/* Purge all references in the cache to NP, either as a node or as a
directory. diskfs_node_refcnt_lock must be held around this call. */
void
_diskfs_purge_cache_deletion (struct node *np)
{
struct lookup_cache *lc, *nxt;
for (lc = lookup_cache_head; lc; lc = nxt)
if (lc->np == np || lc->dp == np)
{
if (lc->prev)
lc->prev->next = lc->next;
if (lc->next)
lc->next->prev = lc->prev;
nxt = lc->next;
free (lc);
}
else
nxt = lc->next;
}
/* 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_cache (struct node *dir, char *name)
{
struct lookup_cache *lc;
size_t len = strlen (name);
spin_lock (&diskfs_node_refcnt_lock);
for (lc = lookup_cache_head; lc; lc = lc->next)
if (lc->dp == dir
&& lc->namelen == len
&& lc->name[0] == name[0]
&& !strcmp (lc->name, name))
{
if (lc->np)
{
lc->np->references++;
statistics.pos_hits++;
spin_unlock (&diskfs_node_refcnt_lock);
return lc->np;
}
else
{
statistics.neg_hits++;
spin_unlock (&diskfs_node_refcnt_lock);
return (struct node *) -1;
}
}
statistics.miss++;
spin_unlock (&diskfs_node_refcnt_lock);
return 0;
}
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