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Subject[PATCH 13/43] FS-Cache: Add cache management [ver #46]
Date
Implement the entry points by which a cache backend may initialise, add,
declare an error upon and withdraw a cache.

Further, an object is created in sysfs under which each cache added will get
an object created:

/sys/fs/fscache/<cachetag>/

All of this is described in Documentation/filesystems/caching/backend-api.txt
added by a previous patch.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>
Acked-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---
fs/fscache/cache.c | 249 ++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/fscache/main.c | 7 +
2 files changed, 256 insertions(+), 0 deletions(-)

diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
index 1a28df3..355172f 100644
--- a/fs/fscache/cache.c
+++ b/fs/fscache/cache.c
@@ -16,6 +16,8 @@

LIST_HEAD(fscache_cache_list);
DECLARE_RWSEM(fscache_addremove_sem);
+DECLARE_WAIT_QUEUE_HEAD(fscache_cache_cleared_wq);
+EXPORT_SYMBOL(fscache_cache_cleared_wq);

static LIST_HEAD(fscache_cache_tag_list);

@@ -164,3 +166,250 @@ no_preference:
_leave(" = %p [first]", cache);
return cache;
}
+
+/**
+ * fscache_init_cache - Initialise a cache record
+ * @cache: The cache record to be initialised
+ * @ops: The cache operations to be installed in that record
+ * @idfmt: Format string to define identifier
+ * @...: sprintf-style arguments
+ *
+ * Initialise a record of a cache and fill in the name.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+void fscache_init_cache(struct fscache_cache *cache,
+ const struct fscache_cache_ops *ops,
+ const char *idfmt,
+ ...)
+{
+ va_list va;
+
+ memset(cache, 0, sizeof(*cache));
+
+ cache->ops = ops;
+
+ va_start(va, idfmt);
+ vsnprintf(cache->identifier, sizeof(cache->identifier), idfmt, va);
+ va_end(va);
+
+ INIT_WORK(&cache->op_gc, NULL);
+ INIT_LIST_HEAD(&cache->link);
+ INIT_LIST_HEAD(&cache->object_list);
+ INIT_LIST_HEAD(&cache->op_gc_list);
+ spin_lock_init(&cache->object_list_lock);
+ spin_lock_init(&cache->op_gc_list_lock);
+}
+EXPORT_SYMBOL(fscache_init_cache);
+
+/**
+ * fscache_add_cache - Declare a cache as being open for business
+ * @cache: The record describing the cache
+ * @ifsdef: The record of the cache object describing the top-level index
+ * @tagname: The tag describing this cache
+ *
+ * Add a cache to the system, making it available for netfs's to use.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+int fscache_add_cache(struct fscache_cache *cache,
+ struct fscache_object *ifsdef,
+ const char *tagname)
+{
+ struct fscache_cache_tag *tag;
+
+ BUG_ON(!cache->ops);
+ BUG_ON(!ifsdef);
+
+ cache->flags = 0;
+ ifsdef->event_mask = ULONG_MAX & ~(1 << FSCACHE_OBJECT_EV_CLEARED);
+ ifsdef->state = FSCACHE_OBJECT_ACTIVE;
+
+ if (!tagname)
+ tagname = cache->identifier;
+
+ BUG_ON(!tagname[0]);
+
+ _enter("{%s.%s},,%s", cache->ops->name, cache->identifier, tagname);
+
+ /* we use the cache tag to uniquely identify caches */
+ tag = __fscache_lookup_cache_tag(tagname);
+ if (IS_ERR(tag))
+ goto nomem;
+
+ if (test_and_set_bit(FSCACHE_TAG_RESERVED, &tag->flags))
+ goto tag_in_use;
+
+ cache->kobj = kobject_create_and_add(tagname, fscache_root);
+ if (!cache->kobj)
+ goto error;
+
+ ifsdef->cookie = &fscache_fsdef_index;
+ ifsdef->cache = cache;
+ cache->fsdef = ifsdef;
+
+ down_write(&fscache_addremove_sem);
+
+ tag->cache = cache;
+ cache->tag = tag;
+
+ /* add the cache to the list */
+ list_add(&cache->link, &fscache_cache_list);
+
+ /* add the cache's netfs definition index object to the cache's
+ * list */
+ spin_lock(&cache->object_list_lock);
+ list_add_tail(&ifsdef->cache_link, &cache->object_list);
+ spin_unlock(&cache->object_list_lock);
+
+ /* add the cache's netfs definition index object to the top level index
+ * cookie as a known backing object */
+ spin_lock(&fscache_fsdef_index.lock);
+
+ hlist_add_head(&ifsdef->cookie_link,
+ &fscache_fsdef_index.backing_objects);
+
+ atomic_inc(&fscache_fsdef_index.usage);
+
+ /* done */
+ spin_unlock(&fscache_fsdef_index.lock);
+ up_write(&fscache_addremove_sem);
+
+ printk(KERN_NOTICE "FS-Cache: Cache \"%s\" added (type %s)\n",
+ cache->tag->name, cache->ops->name);
+ kobject_uevent(cache->kobj, KOBJ_ADD);
+
+ _leave(" = 0 [%s]", cache->identifier);
+ return 0;
+
+tag_in_use:
+ printk(KERN_ERR "FS-Cache: Cache tag '%s' already in use\n", tagname);
+ __fscache_release_cache_tag(tag);
+ _leave(" = -EXIST");
+ return -EEXIST;
+
+error:
+ __fscache_release_cache_tag(tag);
+ _leave(" = -EINVAL");
+ return -EINVAL;
+
+nomem:
+ _leave(" = -ENOMEM");
+ return -ENOMEM;
+}
+EXPORT_SYMBOL(fscache_add_cache);
+
+/**
+ * fscache_io_error - Note a cache I/O error
+ * @cache: The record describing the cache
+ *
+ * Note that an I/O error occurred in a cache and that it should no longer be
+ * used for anything. This also reports the error into the kernel log.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+void fscache_io_error(struct fscache_cache *cache)
+{
+ set_bit(FSCACHE_IOERROR, &cache->flags);
+
+ printk(KERN_ERR "FS-Cache: Cache %s stopped due to I/O error\n",
+ cache->ops->name);
+}
+EXPORT_SYMBOL(fscache_io_error);
+
+/*
+ * request withdrawal of all the objects in a cache
+ * - all the objects being withdrawn are moved onto the supplied list
+ */
+static void fscache_withdraw_all_objects(struct fscache_cache *cache,
+ struct list_head *dying_objects)
+{
+ struct fscache_object *object;
+
+ spin_lock(&cache->object_list_lock);
+
+ while (!list_empty(&cache->object_list)) {
+ object = list_entry(cache->object_list.next,
+ struct fscache_object, cache_link);
+ list_move_tail(&object->cache_link, dying_objects);
+
+ _debug("withdraw %p", object->cookie);
+
+ spin_lock(&object->lock);
+ spin_unlock(&cache->object_list_lock);
+ fscache_raise_event(object, FSCACHE_OBJECT_EV_WITHDRAW);
+ spin_unlock(&object->lock);
+
+ cond_resched();
+ spin_lock(&cache->object_list_lock);
+ }
+
+ spin_unlock(&cache->object_list_lock);
+}
+
+/**
+ * fscache_withdraw_cache - Withdraw a cache from the active service
+ * @cache: The record describing the cache
+ *
+ * Withdraw a cache from service, unbinding all its cache objects from the
+ * netfs cookies they're currently representing.
+ *
+ * See Documentation/filesystems/caching/backend-api.txt for a complete
+ * description.
+ */
+void fscache_withdraw_cache(struct fscache_cache *cache)
+{
+ LIST_HEAD(dying_objects);
+
+ _enter("");
+
+ printk(KERN_NOTICE "FS-Cache: Withdrawing cache \"%s\"\n",
+ cache->tag->name);
+
+ /* make the cache unavailable for cookie acquisition */
+ if (test_and_set_bit(FSCACHE_CACHE_WITHDRAWN, &cache->flags))
+ BUG();
+
+ down_write(&fscache_addremove_sem);
+ list_del_init(&cache->link);
+ cache->tag->cache = NULL;
+ up_write(&fscache_addremove_sem);
+
+ /* make sure all pages pinned by operations on behalf of the netfs are
+ * written to disk */
+ cache->ops->sync_cache(cache);
+
+ /* dissociate all the netfs pages backed by this cache from the block
+ * mappings in the cache */
+ cache->ops->dissociate_pages(cache);
+
+ /* we now have to destroy all the active objects pertaining to this
+ * cache - which we do by passing them off to thread pool to be
+ * disposed of */
+ _debug("destroy");
+
+ fscache_withdraw_all_objects(cache, &dying_objects);
+
+ /* wait for all extant objects to finish their outstanding operations
+ * and go away */
+ _debug("wait for finish");
+ wait_event(fscache_cache_cleared_wq,
+ atomic_read(&cache->object_count) == 0);
+ _debug("wait for clearance");
+ wait_event(fscache_cache_cleared_wq,
+ list_empty(&cache->object_list));
+ _debug("cleared");
+ ASSERT(list_empty(&dying_objects));
+
+ kobject_put(cache->kobj);
+
+ clear_bit(FSCACHE_TAG_RESERVED, &cache->tag->flags);
+ fscache_release_cache_tag(cache->tag);
+ cache->tag = NULL;
+
+ _leave("");
+}
+EXPORT_SYMBOL(fscache_withdraw_cache);
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 7c734b7..c2f3e63 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -56,9 +56,15 @@ static int __init fscache_init(void)
if (ret < 0)
goto error_proc;

+ fscache_root = kobject_create_and_add("fscache", kernel_kobj);
+ if (!fscache_root)
+ goto error_kobj;
+
printk(KERN_NOTICE "FS-Cache: Loaded\n");
return 0;

+error_kobj:
+ fscache_proc_cleanup();
error_proc:
slow_work_unregister_user();
error_slow_work:
@@ -74,6 +80,7 @@ static void __exit fscache_exit(void)
{
_enter("");

+ kobject_put(fscache_root);
fscache_proc_cleanup();
slow_work_unregister_user();
printk(KERN_NOTICE "FS-Cache: Unloaded\n");


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