dm: add cache target

Add a target that allows a fast device such as an SSD to be used as a
cache for a slower device such as a disk.

A plug-in architecture was chosen so that the decisions about which data
to migrate and when are delegated to interchangeable tunable policy
modules.  The first general purpose module we have developed, called
"mq" (multiqueue), follows in the next patch.  Other modules are
under development.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Heinz Mauelshagen <mauelshagen@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 161 insertions, 0 deletions

diff --git a/drivers/md/dm-cache-policy.c b/drivers/md/dm-cache-policy.c
new file mode 100644
index 000000000000..2cbf5fdaac52
--- /dev/null
+++ b/drivers/md/dm-cache-policy.c
@@ -0,0 +1,161 @@
+/*
+ * Copyright (C) 2012 Red Hat. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include "dm-cache-policy-internal.h"
+#include "dm.h"
+
+#include <linux/module.h>
+#include <linux/slab.h>
+
+/*----------------------------------------------------------------*/
+
+#define DM_MSG_PREFIX "cache-policy"
+
+static DEFINE_SPINLOCK(register_lock);
+static LIST_HEAD(register_list);
+
+static struct dm_cache_policy_type *__find_policy(const char *name)
+{
+        struct dm_cache_policy_type *t;
+
+        list_for_each_entry(t, &register_list, list)
+                if (!strcmp(t->name, name))
+                        return t;
+
+        return NULL;
+}
+
+static struct dm_cache_policy_type *__get_policy_once(const char *name)
+{
+        struct dm_cache_policy_type *t = __find_policy(name);
+
+        if (t && !try_module_get(t->owner)) {
+                DMWARN("couldn't get module %s", name);
+                t = ERR_PTR(-EINVAL);
+        }
+
+        return t;
+}
+
+static struct dm_cache_policy_type *get_policy_once(const char *name)
+{
+        struct dm_cache_policy_type *t;
+
+        spin_lock(&register_lock);
+        t = __get_policy_once(name);
+        spin_unlock(&register_lock);
+
+        return t;
+}
+
+static struct dm_cache_policy_type *get_policy(const char *name)
+{
+        struct dm_cache_policy_type *t;
+
+        t = get_policy_once(name);
+        if (IS_ERR(t))
+                return NULL;
+
+        if (t)
+                return t;
+
+        request_module("dm-cache-%s", name);
+
+        t = get_policy_once(name);
+        if (IS_ERR(t))
+                return NULL;
+
+        return t;
+}
+
+static void put_policy(struct dm_cache_policy_type *t)
+{
+        module_put(t->owner);
+}
+
+int dm_cache_policy_register(struct dm_cache_policy_type *type)
+{
+        int r;
+
+        /* One size fits all for now */
+        if (type->hint_size != 0 && type->hint_size != 4) {
+                DMWARN("hint size must be 0 or 4 but %llu supplied.", (unsigned long long) type->hint_size);
+                return -EINVAL;
+        }
+
+        spin_lock(&register_lock);
+        if (__find_policy(type->name)) {
+                DMWARN("attempt to register policy under duplicate name %s", type->name);
+                r = -EINVAL;
+        } else {
+                list_add(&type->list, &register_list);
+                r = 0;
+        }
+        spin_unlock(&register_lock);
+
+        return r;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_register);
+
+void dm_cache_policy_unregister(struct dm_cache_policy_type *type)
+{
+        spin_lock(&register_lock);
+        list_del_init(&type->list);
+        spin_unlock(&register_lock);
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_unregister);
+
+struct dm_cache_policy *dm_cache_policy_create(const char *name,
+                                               dm_cblock_t cache_size,
+                                               sector_t origin_size,
+                                               sector_t cache_block_size)
+{
+        struct dm_cache_policy *p = NULL;
+        struct dm_cache_policy_type *type;
+
+        type = get_policy(name);
+        if (!type) {
+                DMWARN("unknown policy type");
+                return NULL;
+        }
+
+        p = type->create(cache_size, origin_size, cache_block_size);
+        if (!p) {
+                put_policy(type);
+                return NULL;
+        }
+        p->private = type;
+
+        return p;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_create);
+
+void dm_cache_policy_destroy(struct dm_cache_policy *p)
+{
+        struct dm_cache_policy_type *t = p->private;
+
+        p->destroy(p);
+        put_policy(t);
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_destroy);
+
+const char *dm_cache_policy_get_name(struct dm_cache_policy *p)
+{
+        struct dm_cache_policy_type *t = p->private;
+
+        return t->name;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_get_name);
+
+size_t dm_cache_policy_get_hint_size(struct dm_cache_policy *p)
+{
+        struct dm_cache_policy_type *t = p->private;
+
+        return t->hint_size;
+}
+EXPORT_SYMBOL_GPL(dm_cache_policy_get_hint_size);
+
+/*----------------------------------------------------------------*/