FS-Cache: Add cache tag handling

Implement two features of FS-Cache:

 (1) The ability to request and release cache tags - names by which a cache may
     be known to a netfs, and thus selected for use.

 (2) An internal function by which a cache is selected by consulting the netfs,
     if the netfs wishes to be consulted.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>
This commit is contained in:
David Howells 2009-04-03 16:42:37 +01:00
parent a6891645cf
commit 0e04d4cefc
4 changed files with 195 additions and 1 deletions

View file

@ -3,6 +3,7 @@
#
fscache-y := \
cache.o \
fsdef.o \
main.o

166
fs/fscache/cache.c Normal file
View file

@ -0,0 +1,166 @@
/* FS-Cache cache handling
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program 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 of the License, or (at your option) any later version.
*/
#define FSCACHE_DEBUG_LEVEL CACHE
#include <linux/module.h>
#include <linux/slab.h>
#include "internal.h"
LIST_HEAD(fscache_cache_list);
DECLARE_RWSEM(fscache_addremove_sem);
static LIST_HEAD(fscache_cache_tag_list);
/*
* look up a cache tag
*/
struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *name)
{
struct fscache_cache_tag *tag, *xtag;
/* firstly check for the existence of the tag under read lock */
down_read(&fscache_addremove_sem);
list_for_each_entry(tag, &fscache_cache_tag_list, link) {
if (strcmp(tag->name, name) == 0) {
atomic_inc(&tag->usage);
up_read(&fscache_addremove_sem);
return tag;
}
}
up_read(&fscache_addremove_sem);
/* the tag does not exist - create a candidate */
xtag = kzalloc(sizeof(*xtag) + strlen(name) + 1, GFP_KERNEL);
if (!xtag)
/* return a dummy tag if out of memory */
return ERR_PTR(-ENOMEM);
atomic_set(&xtag->usage, 1);
strcpy(xtag->name, name);
/* write lock, search again and add if still not present */
down_write(&fscache_addremove_sem);
list_for_each_entry(tag, &fscache_cache_tag_list, link) {
if (strcmp(tag->name, name) == 0) {
atomic_inc(&tag->usage);
up_write(&fscache_addremove_sem);
kfree(xtag);
return tag;
}
}
list_add_tail(&xtag->link, &fscache_cache_tag_list);
up_write(&fscache_addremove_sem);
return xtag;
}
/*
* release a reference to a cache tag
*/
void __fscache_release_cache_tag(struct fscache_cache_tag *tag)
{
if (tag != ERR_PTR(-ENOMEM)) {
down_write(&fscache_addremove_sem);
if (atomic_dec_and_test(&tag->usage))
list_del_init(&tag->link);
else
tag = NULL;
up_write(&fscache_addremove_sem);
kfree(tag);
}
}
/*
* select a cache in which to store an object
* - the cache addremove semaphore must be at least read-locked by the caller
* - the object will never be an index
*/
struct fscache_cache *fscache_select_cache_for_object(
struct fscache_cookie *cookie)
{
struct fscache_cache_tag *tag;
struct fscache_object *object;
struct fscache_cache *cache;
_enter("");
if (list_empty(&fscache_cache_list)) {
_leave(" = NULL [no cache]");
return NULL;
}
/* we check the parent to determine the cache to use */
spin_lock(&cookie->lock);
/* the first in the parent's backing list should be the preferred
* cache */
if (!hlist_empty(&cookie->backing_objects)) {
object = hlist_entry(cookie->backing_objects.first,
struct fscache_object, cookie_link);
cache = object->cache;
if (object->state >= FSCACHE_OBJECT_DYING ||
test_bit(FSCACHE_IOERROR, &cache->flags))
cache = NULL;
spin_unlock(&cookie->lock);
_leave(" = %p [parent]", cache);
return cache;
}
/* the parent is unbacked */
if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX) {
/* cookie not an index and is unbacked */
spin_unlock(&cookie->lock);
_leave(" = NULL [cookie ub,ni]");
return NULL;
}
spin_unlock(&cookie->lock);
if (!cookie->def->select_cache)
goto no_preference;
/* ask the netfs for its preference */
tag = cookie->def->select_cache(cookie->parent->netfs_data,
cookie->netfs_data);
if (!tag)
goto no_preference;
if (tag == ERR_PTR(-ENOMEM)) {
_leave(" = NULL [nomem tag]");
return NULL;
}
if (!tag->cache) {
_leave(" = NULL [unbacked tag]");
return NULL;
}
if (test_bit(FSCACHE_IOERROR, &tag->cache->flags))
return NULL;
_leave(" = %p [specific]", tag->cache);
return tag->cache;
no_preference:
/* netfs has no preference - just select first cache */
cache = list_entry(fscache_cache_list.next,
struct fscache_cache, link);
_leave(" = %p [first]", cache);
return cache;
}

View file

@ -27,6 +27,15 @@
#define FSCACHE_MIN_THREADS 4
#define FSCACHE_MAX_THREADS 32
/*
* fsc-cache.c
*/
extern struct list_head fscache_cache_list;
extern struct rw_semaphore fscache_addremove_sem;
extern struct fscache_cache *fscache_select_cache_for_object(
struct fscache_cookie *);
/*
* fsc-fsdef.c
*/
@ -168,6 +177,17 @@ extern const struct file_operations fscache_stats_fops;
#define fscache_stat(stat) do {} while (0)
#endif
/*
* raise an event on an object
* - if the event is not masked for that object, then the object is
* queued for attention by the thread pool.
*/
static inline void fscache_raise_event(struct fscache_object *object,
unsigned event)
{
BUG(); // TODO
}
/*****************************************************************************/
/*
* debug tracing

View file

@ -173,6 +173,8 @@ struct fscache_netfs {
* - these are undefined symbols when FS-Cache is not configured and the
* optimiser takes care of not using them
*/
extern struct fscache_cache_tag *__fscache_lookup_cache_tag(const char *);
extern void __fscache_release_cache_tag(struct fscache_cache_tag *);
/**
* fscache_register_netfs - Register a filesystem as desiring caching services
@ -218,7 +220,10 @@ void fscache_unregister_netfs(struct fscache_netfs *netfs)
static inline
struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
{
return NULL;
if (fscache_available())
return __fscache_lookup_cache_tag(name);
else
return NULL;
}
/**
@ -233,6 +238,8 @@ struct fscache_cache_tag *fscache_lookup_cache_tag(const char *name)
static inline
void fscache_release_cache_tag(struct fscache_cache_tag *tag)
{
if (fscache_available())
__fscache_release_cache_tag(tag);
}
/**