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/* Directory name lookup caching
Copyright (C) 1996 Free Software Foundation, Inc.
Written by Michael I. Bushnell, p/BSG, & Miles Bader.
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>
#include <cacheq.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
{
struct cacheq_hdr hdr;
/* Used to indentify nodes to the fs dependent code. 0 for NODE_CACHE_ID
means a `negative' entry -- recording that there's definitely no node with
this name. */
int dir_cache_id, node_cache_id;
/* Name of the node NODE_CACHE_ID in the directory DIR_CACHE_ID. Entries
with names too long to fit in this buffer aren't cached at all. */
char name[CACHE_NAME_LEN];
/* Strlen of NAME. If this is zero, it's an unused entry. */
size_t name_len;
};
/* The contents of the cache in no particular order */
static struct cacheq lookup_cache = { sizeof (struct lookup_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;
/* If there's an entry for NAME, of length NAME_LEN, in directory DIR in the
cache, return it's entry, otherwise 0. CACHE_LOCK must be held. */
static struct lookup_cache *
find_cache (struct node *dir, const char *name, size_t name_len)
{
struct lookup_cache *c;
/* Search the list. All unused entries are contiguous at the end of the
list, so we can stop searching when we see the first one. */
for (c = lookup_cache.mru; c && c->name_len; c = c->hdr.next)
if (c->name_len == name_len
&& c->dir_cache_id == dir->cache_id
&& c->name[0] == name[0] && strcmp (c->name, name) == 0)
return c;
return 0;
}
/* 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)
{
struct lookup_cache *c;
size_t name_len = strlen (name);
if (name_len > CACHE_NAME_LEN - 1)
return;
/* Never cache . or ..; it's too much trouble to get the locking
order right. */
if (name[0] == '.'
&& (name[1] == '\0'
|| (name[1] == '.' && name[2] == '\0')))
return;
spin_lock (&cache_lock);
if (lookup_cache.length == 0)
/* There should always be an lru_cache; this being zero means that the
cache hasn't been initialized yet. Do so. */
cacheq_set_length (&lookup_cache, MAXCACHE);
/* See if there's an old entry for NAME in DIR. If not, replace the least
recently used entry. */
c = find_cache (dir, name, name_len) ?: lookup_cache.lru;
/* Fill C with the new entry. */
c->dir_cache_id = dir->cache_id;
c->node_cache_id = np ? np->cache_id : 0;
strcpy (c->name, name);
c->name_len = name_len;
/* Now C becomes the MRU entry! */
cacheq_make_mru (&lookup_cache, c);
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)
{
struct lookup_cache *c, *next;
spin_lock (&cache_lock);
for (c = lookup_cache.mru; c; c = next)
{
/* Save C->hdr.next, since we may move C from this position. */
next = c->hdr.next;
if (c->name_len
&& c->dir_cache_id == dp->cache_id
&& c->node_cache_id == np->cache_id)
{
c->name_len = 0;
cacheq_make_lru (&lookup_cache, c); /* Use C as the next free
entry. */
}
}
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)
{
struct lookup_cache *c;
spin_lock (&cache_lock);
c = find_cache (dir, name, strlen (name));
if (c)
{
int id = c->node_cache_id;
cacheq_make_mru (&lookup_cache, c); /* Record C as recently used. */
statistics.pos_hits++;
spin_unlock (&cache_lock);
if (id == 0)
/* A negative cache entry. */
return (struct node *)-1;
else if (id == dir->cache_id)
/* The cached node is the same as DIR. */
{
diskfs_nref (dir);
return dir;
}
else
/* Just a normal entry in DIR; get the actual node. */
{
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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