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authorDavid Howells <dhowells@redhat.com>2009-04-03 16:42:37 +0100
committerDavid Howells <dhowells@redhat.com>2009-04-03 16:42:37 +0100
commit0e04d4cefcf4d8fbbdb2c50e93ad541582933fd2 (patch)
tree97c4cda6a2c246660e6a5c718a9272375cdb259c /fs/fscache/cache.c
parenta6891645cf2ddd4778096848a864580e7258faba (diff)
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>
Diffstat (limited to 'fs/fscache/cache.c')
-rw-r--r--fs/fscache/cache.c166
1 files changed, 166 insertions, 0 deletions
diff --git a/fs/fscache/cache.c b/fs/fscache/cache.c
new file mode 100644
index 00000000000..1a28df36dd9
--- /dev/null
+++ b/fs/fscache/cache.c
@@ -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;
+}