dm exception store: introduce registry

Move exception stores into a registry.

Signed-off-by: Jonathan Brassow <jbrassow@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 162 insertions, 0 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index dccbfb0e010f..8912a3637cae 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -14,6 +14,168 @@
 
 #define DM_MSG_PREFIX "snapshot exception stores"
 
+static LIST_HEAD(_exception_store_types);
+static DEFINE_SPINLOCK(_lock);
+
+static struct dm_exception_store_type *__find_exception_store_type(const char *name)
+{
+        struct dm_exception_store_type *type;
+
+        list_for_each_entry(type, &_exception_store_types, list)
+                if (!strcmp(name, type->name))
+                        return type;
+
+        return NULL;
+}
+
+static struct dm_exception_store_type *_get_exception_store_type(const char *name)
+{
+        struct dm_exception_store_type *type;
+
+        spin_lock(&_lock);
+
+        type = __find_exception_store_type(name);
+
+        if (type && !try_module_get(type->module))
+                type = NULL;
+
+        spin_unlock(&_lock);
+
+        return type;
+}
+
+/*
+ * get_type
+ * @type_name
+ *
+ * Attempt to retrieve the dm_exception_store_type by name.  If not already
+ * available, attempt to load the appropriate module.
+ *
+ * Exstore modules are named "dm-exstore-" followed by the 'type_name'.
+ * Modules may contain multiple types.
+ * This function will first try the module "dm-exstore-<type_name>",
+ * then truncate 'type_name' on the last '-' and try again.
+ *
+ * For example, if type_name was "clustered-shared", it would search
+ * 'dm-exstore-clustered-shared' then 'dm-exstore-clustered'.
+ *
+ * 'dm-exception-store-<type_name>' is too long of a name in my
+ * opinion, which is why I've chosen to have the files
+ * containing exception store implementations be 'dm-exstore-<type_name>'.
+ * If you want your module to be autoloaded, you will follow this
+ * naming convention.
+ *
+ * Returns: dm_exception_store_type* on success, NULL on failure
+ */
+static struct dm_exception_store_type *get_type(const char *type_name)
+{
+        char *p, *type_name_dup;
+        struct dm_exception_store_type *type;
+
+        type = _get_exception_store_type(type_name);
+        if (type)
+                return type;
+
+        type_name_dup = kstrdup(type_name, GFP_KERNEL);
+        if (!type_name_dup) {
+                DMERR("No memory left to attempt load for \"%s\"", type_name);
+                return NULL;
+        }
+
+        while (request_module("dm-exstore-%s", type_name_dup) ||
+               !(type = _get_exception_store_type(type_name))) {
+                p = strrchr(type_name_dup, '-');
+                if (!p)
+                        break;
+                p[0] = '\0';
+        }
+
+        if (!type)
+                DMWARN("Module for exstore type \"%s\" not found.", type_name);
+
+        kfree(type_name_dup);
+
+        return type;
+}
+
+static void put_type(struct dm_exception_store_type *type)
+{
+        spin_lock(&_lock);
+        module_put(type->module);
+        spin_unlock(&_lock);
+}
+
+int dm_exception_store_type_register(struct dm_exception_store_type *type)
+{
+        int r = 0;
+
+        spin_lock(&_lock);
+        if (!__find_exception_store_type(type->name))
+                list_add(&type->list, &_exception_store_types);
+        else
+                r = -EEXIST;
+        spin_unlock(&_lock);
+
+        return r;
+}
+EXPORT_SYMBOL(dm_exception_store_type_register);
+
+int dm_exception_store_type_unregister(struct dm_exception_store_type *type)
+{
+        spin_lock(&_lock);
+
+        if (!__find_exception_store_type(type->name)) {
+                spin_unlock(&_lock);
+                return -EINVAL;
+        }
+
+        list_del(&type->list);
+
+        spin_unlock(&_lock);
+
+        return 0;
+}
+EXPORT_SYMBOL(dm_exception_store_type_unregister);
+
+int dm_exception_store_create(const char *type_name,
+                              struct dm_exception_store **store)
+{
+        int r = 0;
+        struct dm_exception_store_type *type;
+        struct dm_exception_store *tmp_store;
+
+        tmp_store = kmalloc(sizeof(*tmp_store), GFP_KERNEL);
+        if (!tmp_store)
+                return -ENOMEM;
+
+        type = get_type(type_name);
+        if (!type) {
+                kfree(tmp_store);
+                return -EINVAL;
+        }
+
+        tmp_store->type = type;
+
+        r = type->ctr(tmp_store, 0, NULL);
+        if (r) {
+                put_type(type);
+                kfree(tmp_store);
+                return r;
+        }
+
+        *store = tmp_store;
+        return 0;
+}
+EXPORT_SYMBOL(dm_exception_store_create);
+
+void dm_exception_store_destroy(struct dm_exception_store *store)
+{
+        store->type->dtr(store);
+        put_type(store->type);
+        kfree(store);
+}
+EXPORT_SYMBOL(dm_exception_store_destroy);
+
 int dm_exception_store_init(void)
 {
         int r;