FS-Cache: Add cache management

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>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Tested-by: Daire Byrne <Daire.Byrne@framestore.com>

2 files changed, 256 insertions, 0 deletions

diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
index 1a28df36dd93..355172f785fb 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 7c734b7fb18e..c2f3e637725d 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");