X-Git-Url: https://git.tokkee.org/?p=sysdb.git;a=blobdiff_plain;f=src%2Fcore%2Fplugin.c;h=3611be4966b51d296557620e9ed77abda9d7ce48;hp=46976d01f7435c580e088f3aebd7836ad14ebbf4;hb=9a96acd759c31211aa512e174339a9c178c4eb83;hpb=6e7b1987b6a571c0f2815b8507ec9373981f058e

diff --git a/src/core/plugin.c b/src/core/plugin.c
index 46976d0..3611be4 100644
--- a/src/core/plugin.c
+++ b/src/core/plugin.c
@@ -25,6 +25,10 @@
  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#if HAVE_CONFIG_H
+#	include "config.h"
+#endif /* HAVE_CONFIG_H */
+
 #include "sysdb.h"
 #include "core/plugin.h"
 #include "core/time.h"
@@ -46,40 +50,28 @@
 
 #include <pthread.h>
 
+/* helper to access info attributes */
+#define INFO_GET(i, attr) \
+	((i)->attr ? (i)->attr : #attr" not set")
+
 /*
  * private data types
  */
 
-struct sdb_plugin_info {
-	char *plugin_name;
-	char *filename;
-
-	/* public attributes */
-	char *name;
-
-	char *description;
-	char *copyright;
-	char *license;
-
-	int   version;
-	int   plugin_version;
-};
-#define SDB_PLUGIN_INFO_INIT { \
-	/* plugin_name */ NULL, /* filename */ NULL, \
-	/* name */ NULL, /* desc */ NULL, \
-	/* copyright */ NULL, /* license */ NULL, \
-	/* version */ -1, /* plugin_version */ -1 }
-#define INFO_GET(i, attr) \
-	((i)->attr ? (i)->attr : #attr" not set")
-
 typedef struct {
 	sdb_object_t super;
 	sdb_plugin_ctx_t public;
 
 	sdb_plugin_info_t info;
+	lt_dlhandle handle;
+
+	/* The usage count differs from the object's ref count
+	 * in that it provides higher level information about how
+	 * the plugin is in use. */
+	size_t use_cnt;
 } ctx_t;
 #define CTX_INIT { SDB_OBJECT_INIT, \
-	SDB_PLUGIN_CTX_INIT, SDB_PLUGIN_INFO_INIT }
+	SDB_PLUGIN_CTX_INIT, SDB_PLUGIN_INFO_INIT, NULL, 0 }
 
 #define CTX(obj) ((ctx_t *)(obj))
 
@@ -88,24 +80,39 @@ typedef struct {
 	void *cb_callback;
 	sdb_object_t *cb_user_data;
 	ctx_t *cb_ctx;
-} sdb_plugin_cb_t;
-#define SDB_PLUGIN_CB_INIT { SDB_OBJECT_INIT, \
+} callback_t;
+#define CB_INIT { SDB_OBJECT_INIT, \
 	/* callback = */ NULL, /* user_data = */ NULL, \
 	SDB_PLUGIN_CTX_INIT }
+#define CB(obj) ((callback_t *)(obj))
+#define CONST_CB(obj) ((const callback_t *)(obj))
 
 typedef struct {
-	sdb_plugin_cb_t super;
+	callback_t super;
 #define ccb_callback super.cb_callback
 #define ccb_user_data super.cb_user_data
 #define ccb_ctx super.cb_ctx
 	sdb_time_t ccb_interval;
 	sdb_time_t ccb_next_update;
-} sdb_plugin_collector_cb_t;
+} collector_t;
+#define CCB(obj) ((collector_t *)(obj))
+#define CONST_CCB(obj) ((const collector_t *)(obj))
 
-#define SDB_PLUGIN_CB(obj) ((sdb_plugin_cb_t *)(obj))
-#define SDB_CONST_PLUGIN_CB(obj) ((const sdb_plugin_cb_t *)(obj))
-#define SDB_PLUGIN_CCB(obj) ((sdb_plugin_collector_cb_t *)(obj))
-#define SDB_CONST_PLUGIN_CCB(obj) ((const sdb_plugin_collector_cb_t *)(obj))
+typedef struct {
+	callback_t super; /* cb_callback will always be NULL */
+#define w_user_data super.cb_user_data
+#define w_ctx super.cb_ctx
+	sdb_store_writer_t impl;
+} writer_t;
+#define WRITER(obj) ((writer_t *)(obj))
+
+typedef struct {
+	callback_t super; /* cb_callback will always be NULL */
+#define r_user_data super.cb_user_data
+#define r_ctx super.cb_ctx
+	sdb_store_reader_t impl;
+} reader_t;
+#define READER(obj) ((reader_t *)(obj))
 
 /*
  * private variables
@@ -115,7 +122,7 @@ static sdb_plugin_ctx_t  plugin_default_ctx  = SDB_PLUGIN_CTX_INIT;
 static sdb_plugin_info_t plugin_default_info = SDB_PLUGIN_INFO_INIT;
 
 static pthread_key_t     plugin_ctx_key;
-static _Bool             plugin_ctx_key_initialized = 0;
+static bool              plugin_ctx_key_initialized = 0;
 
 /* a list of the plugin contexts of all registered plugins */
 static sdb_llist_t      *all_plugins = NULL;
@@ -126,6 +133,24 @@ static sdb_llist_t      *collector_list = NULL;
 static sdb_llist_t      *cname_list = NULL;
 static sdb_llist_t      *shutdown_list = NULL;
 static sdb_llist_t      *log_list = NULL;
+static sdb_llist_t      *ts_fetcher_list = NULL;
+static sdb_llist_t      *writer_list = NULL;
+static sdb_llist_t      *reader_list = NULL;
+
+static struct {
+	const char   *type;
+	sdb_llist_t **list;
+} all_lists[] = {
+	{ "config",             &config_list },
+	{ "init",               &init_list },
+	{ "collector",          &collector_list },
+	{ "cname",              &cname_list },
+	{ "shutdown",           &shutdown_list },
+	{ "log",                &log_list },
+	{ "timeseries fetcher", &ts_fetcher_list },
+	{ "store writer",       &writer_list },
+	{ "store reader",       &reader_list },
+};
 
 /*
  * private helper functions
@@ -143,8 +168,6 @@ plugin_info_clear(sdb_plugin_info_t *info)
 	if (info->filename)
 		free(info->filename);
 
-	if (info->name)
-		free(info->name);
 	if (info->description)
 		free(info->description);
 	if (info->copyright)
@@ -168,10 +191,8 @@ ctx_key_init(void)
 static int
 plugin_cmp_next_update(const sdb_object_t *a, const sdb_object_t *b)
 {
-	const sdb_plugin_collector_cb_t *ccb1
-		= (const sdb_plugin_collector_cb_t *)a;
-	const sdb_plugin_collector_cb_t *ccb2
-		= (const sdb_plugin_collector_cb_t *)b;
+	const collector_t *ccb1 = (const collector_t *)a;
+	const collector_t *ccb2 = (const collector_t *)b;
 
 	assert(ccb1 && ccb2);
 
@@ -183,50 +204,59 @@ plugin_cmp_next_update(const sdb_object_t *a, const sdb_object_t *b)
 static int
 plugin_lookup_by_name(const sdb_object_t *obj, const void *id)
 {
-	const sdb_plugin_cb_t *cb = SDB_CONST_PLUGIN_CB(obj);
+	const callback_t *cb = CONST_CB(obj);
 	const char *name = id;
 
-	assert(cb && id && cb->cb_ctx);
+	assert(cb && id);
+
+	/* when a plugin was registered from outside a plugin (e.g. the core),
+	 * we don't have a plugin context */
+	if (! cb->cb_ctx)
+		return 1;
+
 	if (!strcasecmp(cb->cb_ctx->info.plugin_name, name))
 		return 0;
 	return 1;
 } /* plugin_lookup_by_name */
 
+/* since this function is called from sdb_plugin_reconfigure_finish()
+ * when iterating through all_plugins, we may not do any additional
+ * modifications to all_plugins except for the optional removal */
 static void
 plugin_unregister_by_name(const char *plugin_name)
 {
+	sdb_object_t *obj;
 	size_t i;
 
-	struct {
-		const char  *type;
-		sdb_llist_t *list;
-	} all_lists[] = {
-		{ "config",    config_list },
-		{ "init",      init_list },
-		{ "collector", collector_list },
-		{ "cname",     cname_list },
-		{ "shutdown",  shutdown_list },
-		{ "log",       log_list },
-	};
-
 	for (i = 0; i < SDB_STATIC_ARRAY_LEN(all_lists); ++i) {
-		const char  *type = all_lists[i].type;
-		sdb_llist_t *list = all_lists[i].list;
+		const char  *type =  all_lists[i].type;
+		sdb_llist_t *list = *all_lists[i].list;
 
 		while (1) {
-			sdb_object_t *obj = sdb_llist_remove(list,
-					plugin_lookup_by_name, plugin_name);
-			sdb_plugin_cb_t *cb = SDB_PLUGIN_CB(obj);
+			callback_t *cb;
 
-			if (! obj)
+			cb = CB(sdb_llist_remove(list,
+						plugin_lookup_by_name, plugin_name));
+			if (! cb)
 				break;
 
+			assert(cb->cb_ctx);
+
 			sdb_log(SDB_LOG_INFO, "core: Unregistering "
-					"%s callback '%s' (module %s)", type, obj->name,
+					"%s callback '%s' (module %s)", type, cb->super.name,
 					cb->cb_ctx->info.plugin_name);
-			sdb_object_deref(obj);
+			sdb_object_deref(SDB_OBJ(cb));
 		}
 	}
+
+	obj = sdb_llist_search_by_name(all_plugins, plugin_name);
+	/* when called from sdb_plugin_reconfigure_finish, the object has already
+	 * been removed from the list */
+	if (obj && (obj->ref_cnt <= 1)) {
+		sdb_llist_remove_by_name(all_plugins, plugin_name);
+		sdb_object_deref(obj);
+	}
+	/* else: other callbacks still reference it */
 } /* plugin_unregister_by_name */
 
 /*
@@ -242,6 +272,8 @@ ctx_init(sdb_object_t *obj, va_list __attribute__((unused)) ap)
 
 	ctx->public = plugin_default_ctx;
 	ctx->info = plugin_default_info;
+	ctx->handle = NULL;
+	ctx->use_cnt = 1;
 	return 0;
 } /* ctx_init */
 
@@ -249,6 +281,20 @@ static void
 ctx_destroy(sdb_object_t *obj)
 {
 	ctx_t *ctx = CTX(obj);
+
+	if (ctx->handle) {
+		const char *err;
+
+		sdb_log(SDB_LOG_INFO, "core: Unloading module %s",
+				ctx->info.plugin_name);
+
+		lt_dlerror();
+		lt_dlclose(ctx->handle);
+		if ((err = lt_dlerror()))
+			sdb_log(SDB_LOG_WARNING, "core: Failed to unload module %s: %s",
+					ctx->info.plugin_name, err);
+	}
+
 	plugin_info_clear(&ctx->info);
 } /* ctx_destroy */
 
@@ -259,21 +305,6 @@ static sdb_type_t ctx_type = {
 	ctx_destroy
 };
 
-static ctx_t *
-ctx_create(const char *name)
-{
-	ctx_t *ctx;
-
-	ctx = CTX(sdb_object_create(name, ctx_type));
-	if (! ctx)
-		return NULL;
-
-	if (! plugin_ctx_key_initialized)
-		ctx_key_init();
-	pthread_setspecific(plugin_ctx_key, ctx);
-	return ctx;
-} /* ctx_create */
-
 static ctx_t *
 ctx_get(void)
 {
@@ -291,10 +322,29 @@ ctx_set(ctx_t *new)
 		ctx_key_init();
 
 	old = pthread_getspecific(plugin_ctx_key);
+	if (old)
+		sdb_object_deref(SDB_OBJ(old));
+	if (new)
+		sdb_object_ref(SDB_OBJ(new));
 	pthread_setspecific(plugin_ctx_key, new);
 	return old;
 } /* ctx_set */
 
+static ctx_t *
+ctx_create(const char *name)
+{
+	ctx_t *ctx;
+
+	ctx = CTX(sdb_object_create(name, ctx_type));
+	if (! ctx)
+		return NULL;
+
+	if (! plugin_ctx_key_initialized)
+		ctx_key_init();
+	ctx_set(ctx);
+	return ctx;
+} /* ctx_create */
+
 static int
 plugin_cb_init(sdb_object_t *obj, va_list ap)
 {
@@ -314,12 +364,14 @@ plugin_cb_init(sdb_object_t *obj, va_list ap)
 		return -1;
 	}
 
-	SDB_PLUGIN_CB(obj)->cb_callback = callback;
-	SDB_PLUGIN_CB(obj)->cb_ctx      = ctx_get();
-	sdb_object_ref(SDB_OBJ(SDB_PLUGIN_CB(obj)->cb_ctx));
+	/* cb_ctx may be NULL if the plugin was not registered by a plugin */
+
+	CB(obj)->cb_callback = callback;
+	CB(obj)->cb_ctx      = ctx_get();
+	sdb_object_ref(SDB_OBJ(CB(obj)->cb_ctx));
 
 	sdb_object_ref(ud);
-	SDB_PLUGIN_CB(obj)->cb_user_data = ud;
+	CB(obj)->cb_user_data = ud;
 	return 0;
 } /* plugin_cb_init */
 
@@ -327,92 +379,173 @@ static void
 plugin_cb_destroy(sdb_object_t *obj)
 {
 	assert(obj);
-	sdb_object_deref(SDB_PLUGIN_CB(obj)->cb_user_data);
-	sdb_object_deref(SDB_OBJ(SDB_PLUGIN_CB(obj)->cb_ctx));
+	sdb_object_deref(CB(obj)->cb_user_data);
+	sdb_object_deref(SDB_OBJ(CB(obj)->cb_ctx));
 } /* plugin_cb_destroy */
 
-static sdb_type_t sdb_plugin_cb_type = {
-	sizeof(sdb_plugin_cb_t),
+static sdb_type_t callback_type = {
+	sizeof(callback_t),
 
 	plugin_cb_init,
 	plugin_cb_destroy
 };
 
-static sdb_type_t sdb_plugin_collector_cb_type = {
-	sizeof(sdb_plugin_collector_cb_t),
+static sdb_type_t collector_type = {
+	sizeof(collector_t),
 
 	plugin_cb_init,
 	plugin_cb_destroy
 };
 
 static int
-plugin_add_callback(sdb_llist_t **list, const char *type,
-		const char *name, void *callback, sdb_object_t *user_data)
+plugin_writer_init(sdb_object_t *obj, va_list ap)
 {
-	sdb_object_t *obj;
+	sdb_store_writer_t *impl = va_arg(ap, sdb_store_writer_t *);
+	sdb_object_t       *ud   = va_arg(ap, sdb_object_t *);
 
-	if ((! name) || (! callback))
+	assert(impl);
+
+	if ((! impl->store_host) || (! impl->store_service)
+			|| (! impl->store_metric) || (! impl->store_attribute)) {
+		sdb_log(SDB_LOG_ERR, "core: store writer callback '%s' "
+				"does not fully implement the writer interface.",
+				obj->name);
+		return -1;
+	}
+	if (sdb_llist_search_by_name(writer_list, obj->name)) {
+		sdb_log(SDB_LOG_WARNING, "core: store writer callback '%s' "
+				"has already been registered. Ignoring newly "
+				"registered version.", obj->name);
 		return -1;
+	}
 
-	assert(list);
+	/* ctx may be NULL if the callback was not registered by a plugin */
 
-	if (! *list)
-		*list = sdb_llist_create();
-	if (! *list)
-		return -1;
+	WRITER(obj)->impl = *impl;
+	WRITER(obj)->w_ctx  = ctx_get();
+	sdb_object_ref(SDB_OBJ(WRITER(obj)->w_ctx));
 
-	obj = sdb_object_create(name, sdb_plugin_cb_type,
-			list, type, callback, user_data);
-	if (! obj)
-		return -1;
+	sdb_object_ref(ud);
+	WRITER(obj)->w_user_data = ud;
+	return 0;
+} /* plugin_writer_init */
 
-	if (sdb_llist_append(*list, obj)) {
-		sdb_object_deref(obj);
+static void
+plugin_writer_destroy(sdb_object_t *obj)
+{
+	assert(obj);
+	sdb_object_deref(WRITER(obj)->w_user_data);
+	sdb_object_deref(SDB_OBJ(WRITER(obj)->w_ctx));
+} /* plugin_writer_destroy */
+
+static sdb_type_t writer_type = {
+	sizeof(writer_t),
+
+	plugin_writer_init,
+	plugin_writer_destroy
+};
+
+static int
+plugin_reader_init(sdb_object_t *obj, va_list ap)
+{
+	sdb_store_reader_t *impl = va_arg(ap, sdb_store_reader_t *);
+	sdb_object_t       *ud   = va_arg(ap, sdb_object_t *);
+
+	assert(impl);
+
+	if ((! impl->prepare_query) || (! impl->execute_query)) {
+		sdb_log(SDB_LOG_ERR, "core: store reader callback '%s' "
+				"does not fully implement the reader interface.",
+				obj->name);
+		return -1;
+	}
+	if (sdb_llist_search_by_name(reader_list, obj->name)) {
+		sdb_log(SDB_LOG_WARNING, "core: store reader callback '%s' "
+				"has already been registered. Ignoring newly "
+				"registered version.", obj->name);
 		return -1;
 	}
 
-	/* pass control to the list */
-	sdb_object_deref(obj);
+	/* ctx may be NULL if the callback was not registered by a plugin */
 
-	sdb_log(SDB_LOG_INFO, "core: Registered %s callback '%s'.",
-			type, name);
+	READER(obj)->impl = *impl;
+	READER(obj)->r_ctx  = ctx_get();
+	sdb_object_ref(SDB_OBJ(READER(obj)->r_ctx));
+
+	sdb_object_ref(ud);
+	READER(obj)->r_user_data = ud;
 	return 0;
-} /* plugin_add_callback */
+} /* plugin_reader_init */
 
-/*
- * public API
- */
+static void
+plugin_reader_destroy(sdb_object_t *obj)
+{
+	assert(obj);
+	sdb_object_deref(READER(obj)->r_user_data);
+	sdb_object_deref(SDB_OBJ(READER(obj)->r_ctx));
+} /* plugin_reader_destroy */
 
-int
-sdb_plugin_load(const char *name, const sdb_plugin_ctx_t *plugin_ctx)
+static sdb_type_t reader_type = {
+	sizeof(reader_t),
+
+	plugin_reader_init,
+	plugin_reader_destroy
+};
+
+static int
+module_init(const char *name, lt_dlhandle lh, sdb_plugin_info_t *info)
+{
+	int (*mod_init)(sdb_plugin_info_t *);
+	int status;
+
+	mod_init = (int (*)(sdb_plugin_info_t *))lt_dlsym(lh, "sdb_module_init");
+	if (! mod_init) {
+		sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
+				"could not find symbol 'sdb_module_init'", name);
+		return -1;
+	}
+
+	status = mod_init(info);
+	if (status) {
+		sdb_log(SDB_LOG_ERR, "core: Failed to initialize "
+				"module '%s'", name);
+		plugin_unregister_by_name(name);
+		return -1;
+	}
+	return 0;
+} /* module_init */
+
+static int
+module_load(const char *basedir, const char *name,
+		const sdb_plugin_ctx_t *plugin_ctx)
 {
-	char  real_name[strlen(name) > 0 ? strlen(name) : 1];
+	char  base_name[name ? strlen(name) + 1 : 1];
 	const char *name_ptr;
 	char *tmp;
 
 	char filename[1024];
-	ctx_t *ctx;
-
 	lt_dlhandle lh;
 
-	int (*mod_init)(sdb_plugin_info_t *);
+	ctx_t *ctx;
+
 	int status;
 
-	if ((! name) || (! *name))
-		return -1;
+	assert(name);
 
-	real_name[0] = '\0';
+	base_name[0] = '\0';
 	name_ptr = name;
 
 	while ((tmp = strstr(name_ptr, "::"))) {
-		strncat(real_name, name_ptr, (size_t)(tmp - name_ptr));
-		strcat(real_name, "/");
+		strncat(base_name, name_ptr, (size_t)(tmp - name_ptr));
+		strcat(base_name, "/");
 		name_ptr = tmp + strlen("::");
 	}
-	strcat(real_name, name_ptr);
+	strcat(base_name, name_ptr);
+
+	if (! basedir)
+		basedir = PKGLIBDIR;
 
-	snprintf(filename, sizeof(filename), "%s/%s.so",
-			PKGLIBDIR, real_name);
+	snprintf(filename, sizeof(filename), "%s/%s.so", basedir, base_name);
 	filename[sizeof(filename) - 1] = '\0';
 
 	if (access(filename, R_OK)) {
@@ -436,7 +569,7 @@ sdb_plugin_load(const char *name, const sdb_plugin_ctx_t *plugin_ctx)
 	if (ctx_get())
 		sdb_log(SDB_LOG_WARNING, "core: Discarding old plugin context");
 
-	ctx = ctx_create(real_name);
+	ctx = ctx_create(name);
 	if (! ctx) {
 		sdb_log(SDB_LOG_ERR, "core: Failed to initialize plugin context");
 		return -1;
@@ -444,25 +577,14 @@ sdb_plugin_load(const char *name, const sdb_plugin_ctx_t *plugin_ctx)
 
 	ctx->info.plugin_name = strdup(name);
 	ctx->info.filename = strdup(filename);
+	ctx->handle = lh;
 
 	if (plugin_ctx)
 		ctx->public = *plugin_ctx;
 
-	mod_init = (int (*)(sdb_plugin_info_t *))lt_dlsym(lh, "sdb_module_init");
-	if (! mod_init) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
-				"could not find symbol 'sdb_module_init'", name);
-		sdb_object_deref(SDB_OBJ(ctx));
-		return -1;
-	}
-
-	status = mod_init(&ctx->info);
-	if (status) {
-		sdb_log(SDB_LOG_ERR, "core: Failed to initialize "
-				"module '%s'", name);
-		plugin_unregister_by_name(ctx->info.plugin_name);
+	if ((status = module_init(name, lh, &ctx->info))) {
 		sdb_object_deref(SDB_OBJ(ctx));
-		return -1;
+		return status;
 	}
 
 	/* compare minor version */
@@ -474,22 +596,14 @@ sdb_plugin_load(const char *name, const sdb_plugin_ctx_t *plugin_ctx)
 				name, SDB_VERSION_DECODE(ctx->info.version),
 				SDB_VERSION_DECODE(SDB_VERSION));
 
-	if (! all_plugins) {
-		if (! (all_plugins = sdb_llist_create())) {
-			sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
-					"internal error while creating linked list", name);
-			plugin_unregister_by_name(ctx->info.plugin_name);
-			sdb_object_deref(SDB_OBJ(ctx));
-			return -1;
-		}
-	}
-
 	sdb_llist_append(all_plugins, SDB_OBJ(ctx));
 
 	sdb_log(SDB_LOG_INFO, "core: Successfully loaded "
-			"plugin '%s' v%i (%s)\n\t%s\n\tLicense: %s",
-			INFO_GET(&ctx->info, name), ctx->info.plugin_version,
-			INFO_GET(&ctx->info, description),
+			"plugin %s v%i (%s)", ctx->info.plugin_name,
+			ctx->info.plugin_version,
+			INFO_GET(&ctx->info, description));
+	sdb_log(SDB_LOG_INFO, "core: Plugin %s: %s, License: %s",
+			ctx->info.plugin_name,
 			INFO_GET(&ctx->info, copyright),
 			INFO_GET(&ctx->info, license));
 
@@ -499,6 +613,113 @@ sdb_plugin_load(const char *name, const sdb_plugin_ctx_t *plugin_ctx)
 	/* reset */
 	ctx_set(NULL);
 	return 0;
+} /* module_load */
+
+static char *
+plugin_get_name(const char *name, char *buf, size_t bufsize)
+{
+	ctx_t *ctx = ctx_get();
+
+	if (ctx)
+		snprintf(buf, bufsize, "%s::%s", ctx->info.plugin_name, name);
+	else
+		snprintf(buf, bufsize, "core::%s", name);
+	return buf;
+} /* plugin_get_name */
+
+static int
+plugin_add_callback(sdb_llist_t **list, const char *type,
+		const char *name, void *callback, sdb_object_t *user_data)
+{
+	sdb_object_t *obj;
+
+	if ((! name) || (! callback))
+		return -1;
+
+	assert(list);
+
+	if (! *list)
+		*list = sdb_llist_create();
+	if (! *list)
+		return -1;
+
+	obj = sdb_object_create(name, callback_type,
+			list, type, callback, user_data);
+	if (! obj)
+		return -1;
+
+	if (sdb_llist_append(*list, obj)) {
+		sdb_object_deref(obj);
+		return -1;
+	}
+
+	/* pass control to the list */
+	sdb_object_deref(obj);
+
+	sdb_log(SDB_LOG_INFO, "core: Registered %s callback '%s'.",
+			type, name);
+	return 0;
+} /* plugin_add_callback */
+
+static void
+get_backend(char **backends, size_t *backends_num)
+{
+	const sdb_plugin_info_t *info;
+
+	info = sdb_plugin_current();
+	if ((! info) || (! info->plugin_name) || (! *info->plugin_name)) {
+		*backends_num = 0;
+		return;
+	}
+
+	backends[0] = info->plugin_name;
+	*backends_num = 1;
+} /* get_backend */
+
+/*
+ * public API
+ */
+
+int
+sdb_plugin_load(const char *basedir, const char *name,
+		const sdb_plugin_ctx_t *plugin_ctx)
+{
+	ctx_t *ctx;
+
+	int status;
+
+	if ((! name) || (! *name))
+		return -1;
+
+	if (! all_plugins) {
+		if (! (all_plugins = sdb_llist_create())) {
+			sdb_log(SDB_LOG_ERR, "core: Failed to load plugin '%s': "
+					"internal error while creating linked list", name);
+			return -1;
+		}
+	}
+
+	ctx = CTX(sdb_llist_search_by_name(all_plugins, name));
+	if (ctx) {
+		/* plugin already loaded */
+		if (! ctx->use_cnt) {
+			/* reloading plugin */
+			ctx_t *old_ctx = ctx_set(ctx);
+
+			status = module_init(ctx->info.plugin_name, ctx->handle, NULL);
+			if (status)
+				return status;
+
+			sdb_log(SDB_LOG_INFO, "core: Successfully reloaded plugin "
+					"'%s' (%s)", ctx->info.plugin_name,
+					INFO_GET(&ctx->info, description));
+			ctx_set(old_ctx);
+		}
+		++ctx->use_cnt;
+		return 0;
+	}
+
+	return module_load(basedir, name, plugin_ctx);
 } /* sdb_plugin_load */
 
 int
@@ -512,16 +733,6 @@ sdb_plugin_set_info(sdb_plugin_info_t *info, int type, ...)
 	va_start(ap, type);
 
 	switch (type) {
-		case SDB_PLUGIN_INFO_NAME:
-			{
-				char *name = va_arg(ap, char *);
-				if (name) {
-					if (info->name)
-						free(info->name);
-					info->name = strdup(name);
-				}
-			}
-			break;
 		case SDB_PLUGIN_INFO_DESC:
 			{
 				char *desc = va_arg(ap, char *);
@@ -571,48 +782,64 @@ sdb_plugin_set_info(sdb_plugin_info_t *info, int type, ...)
 } /* sdb_plugin_set_info */
 
 int
-sdb_plugin_register_config(const char *name, sdb_plugin_config_cb callback)
+sdb_plugin_register_config(sdb_plugin_config_cb callback)
 {
-	return plugin_add_callback(&config_list, "init", name,
-			callback, NULL);
+	ctx_t *ctx = ctx_get();
+
+	if (! ctx) {
+		sdb_log(SDB_LOG_ERR, "core: Invalid attempt to register a "
+				"config callback from outside a plugin");
+		return -1;
+	}
+	return plugin_add_callback(&config_list, "config", ctx->info.plugin_name,
+			(void *)callback, NULL);
 } /* sdb_plugin_register_config */
 
 int
 sdb_plugin_register_init(const char *name, sdb_plugin_init_cb callback,
 		sdb_object_t *user_data)
 {
-	return plugin_add_callback(&init_list, "init", name,
-			callback, user_data);
+	char cb_name[1024];
+	return plugin_add_callback(&init_list, "init",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			(void *)callback, user_data);
 } /* sdb_plugin_register_init */
 
 int
 sdb_plugin_register_shutdown(const char *name, sdb_plugin_shutdown_cb callback,
 		sdb_object_t *user_data)
 {
-	return plugin_add_callback(&shutdown_list, "shutdown", name,
-			callback, user_data);
+	char cb_name[1024];
+	return plugin_add_callback(&shutdown_list, "shutdown",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			(void *)callback, user_data);
 } /* sdb_plugin_register_shutdown */
 
 int
 sdb_plugin_register_log(const char *name, sdb_plugin_log_cb callback,
 		sdb_object_t *user_data)
 {
-	return plugin_add_callback(&log_list, "log", name, callback,
-			user_data);
+	char cb_name[1024];
+	return plugin_add_callback(&log_list, "log",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			callback, user_data);
 } /* sdb_plugin_register_log */
 
 int
 sdb_plugin_register_cname(const char *name, sdb_plugin_cname_cb callback,
 		sdb_object_t *user_data)
 {
-	return plugin_add_callback(&cname_list, "cname", name, callback,
-			user_data);
+	char cb_name[1024];
+	return plugin_add_callback(&cname_list, "cname",
+			plugin_get_name(name, cb_name, sizeof(cb_name)),
+			callback, user_data);
 } /* sdb_plugin_register_cname */
 
 int
 sdb_plugin_register_collector(const char *name, sdb_plugin_collector_cb callback,
 		const sdb_time_t *interval, sdb_object_t *user_data)
 {
+	char cb_name[1024];
 	sdb_object_t *obj;
 
 	if ((! name) || (! callback))
@@ -623,23 +850,29 @@ sdb_plugin_register_collector(const char *name, sdb_plugin_collector_cb callback
 	if (! collector_list)
 		return -1;
 
-	obj = sdb_object_create(name, sdb_plugin_collector_cb_type,
+	plugin_get_name(name, cb_name, sizeof(cb_name));
+
+	obj = sdb_object_create(cb_name, collector_type,
 			&collector_list, "collector", callback, user_data);
 	if (! obj)
 		return -1;
 
 	if (interval)
-		SDB_PLUGIN_CCB(obj)->ccb_interval = *interval;
+		CCB(obj)->ccb_interval = *interval;
 	else {
-		sdb_time_t tmp = sdb_plugin_get_ctx().interval;
+		ctx_t *ctx = ctx_get();
 
-		if (tmp > 0)
-			SDB_PLUGIN_CCB(obj)->ccb_interval = tmp;
-		else
-			SDB_PLUGIN_CCB(obj)->ccb_interval = 0;
+		if (! ctx) {
+			sdb_log(SDB_LOG_ERR, "core: Cannot determine interval "
+					"for collector %s; none specified and no plugin "
+					"context found", cb_name);
+			return -1;
+		}
+
+		CCB(obj)->ccb_interval = ctx->public.interval;
 	}
 
-	if (! (SDB_PLUGIN_CCB(obj)->ccb_next_update = sdb_gettime())) {
+	if (! (CCB(obj)->ccb_next_update = sdb_gettime())) {
 		char errbuf[1024];
 		sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
 				"time: %s", sdb_strerror(errno, errbuf, sizeof(errbuf)));
@@ -657,21 +890,119 @@ sdb_plugin_register_collector(const char *name, sdb_plugin_collector_cb callback
 	sdb_object_deref(obj);
 
 	sdb_log(SDB_LOG_INFO, "core: Registered collector callback '%s' "
-			"(interval = %.3fs).", name,
-			SDB_TIME_TO_DOUBLE(SDB_PLUGIN_CCB(obj)->ccb_interval));
+			"(interval = %.3fs).", cb_name,
+			SDB_TIME_TO_DOUBLE(CCB(obj)->ccb_interval));
 	return 0;
 } /* sdb_plugin_register_collector */
 
-sdb_plugin_ctx_t
-sdb_plugin_get_ctx(void)
+int
+sdb_plugin_register_ts_fetcher(const char *name,
+		sdb_plugin_fetch_ts_cb callback, sdb_object_t *user_data)
 {
-	ctx_t *c;
+	return plugin_add_callback(&ts_fetcher_list, "time-series fetcher",
+			name, callback, user_data);
+} /* sdb_plugin_register_ts_fetcher */
 
-	c = ctx_get();
-	if (! c) {
-		sdb_plugin_log(SDB_LOG_ERR, "core: Invalid read access to plugin "
-				"context outside a plugin");
-		return plugin_default_ctx;
+int
+sdb_plugin_register_writer(const char *name,
+		sdb_store_writer_t *writer, sdb_object_t *user_data)
+{
+	char cb_name[1024];
+	sdb_object_t *obj;
+
+	if ((! name) || (! writer))
+		return -1;
+
+	if (! writer_list)
+		writer_list = sdb_llist_create();
+	if (! writer_list)
+		return -1;
+
+	plugin_get_name(name, cb_name, sizeof(cb_name));
+
+	obj = sdb_object_create(cb_name, writer_type,
+			writer, user_data);
+	if (! obj)
+		return -1;
+
+	if (sdb_llist_append(writer_list, obj)) {
+		sdb_object_deref(obj);
+		return -1;
+	}
+
+	/* pass control to the list */
+	sdb_object_deref(obj);
+
+	sdb_log(SDB_LOG_INFO, "core: Registered store writer callback '%s'.",
+			cb_name);
+	return 0;
+} /* sdb_store_register_writer */
+
+int
+sdb_plugin_register_reader(const char *name,
+		sdb_store_reader_t *reader, sdb_object_t *user_data)
+{
+	char cb_name[1024];
+	sdb_object_t *obj;
+
+	if ((! name) || (! reader))
+		return -1;
+
+	if (! reader_list)
+		reader_list = sdb_llist_create();
+	if (! reader_list)
+		return -1;
+
+	plugin_get_name(name, cb_name, sizeof(cb_name));
+
+	obj = sdb_object_create(cb_name, reader_type,
+			reader, user_data);
+	if (! obj)
+		return -1;
+
+	if (sdb_llist_append(reader_list, obj)) {
+		sdb_object_deref(obj);
+		return -1;
+	}
+
+	/* pass control to the list */
+	sdb_object_deref(obj);
+
+	sdb_log(SDB_LOG_INFO, "core: Registered store reader callback '%s'.",
+			cb_name);
+	return 0;
+} /* sdb_plugin_register_reader */
+
+void
+sdb_plugin_unregister_all(void)
+{
+	size_t i;
+
+	for (i = 0; i < SDB_STATIC_ARRAY_LEN(all_lists); ++i) {
+		const char  *type =  all_lists[i].type;
+		sdb_llist_t *list = *all_lists[i].list;
+
+		size_t len = sdb_llist_len(list);
+
+		if (! len)
+			continue;
+
+		sdb_llist_clear(list);
+		sdb_log(SDB_LOG_INFO, "core: Unregistered %zu %s callback%s",
+				len, type, len == 1 ? "" : "s");
+	}
+} /* sdb_plugin_unregister_all */
+
+sdb_plugin_ctx_t
+sdb_plugin_get_ctx(void)
+{
+	ctx_t *c;
+
+	c = ctx_get();
+	if (! c) {
+		sdb_plugin_log(SDB_LOG_ERR, "core: Invalid read access to plugin "
+				"context outside a plugin");
+		return plugin_default_ctx;
 	}
 	return c->public;
 } /* sdb_plugin_get_ctx */
@@ -694,10 +1025,20 @@ sdb_plugin_set_ctx(sdb_plugin_ctx_t ctx, sdb_plugin_ctx_t *old)
 	return 0;
 } /* sdb_plugin_set_ctx */
 
+const sdb_plugin_info_t *
+sdb_plugin_current(void)
+{
+	ctx_t *ctx = ctx_get();
+
+	if (! ctx)
+		return NULL;
+	return &ctx->info;
+} /* sdb_plugin_current */
+
 int
 sdb_plugin_configure(const char *name, oconfig_item_t *ci)
 {
-	sdb_plugin_cb_t *plugin;
+	callback_t *plugin;
 	sdb_plugin_config_cb callback;
 
 	ctx_t *old_ctx;
@@ -707,12 +1048,13 @@ sdb_plugin_configure(const char *name, oconfig_item_t *ci)
 	if ((! name) || (! ci))
 		return -1;
 
-	plugin = SDB_PLUGIN_CB(sdb_llist_search_by_name(config_list, name));
+	plugin = CB(sdb_llist_search_by_name(config_list, name));
 	if (! plugin) {
-		/* XXX: check if any such plugin has been loaded */
 		ctx_t *ctx = CTX(sdb_llist_search_by_name(all_plugins, name));
 		if (! ctx)
-			sdb_log(SDB_LOG_ERR, "core: Plugin '%s' not loaded.", name);
+			sdb_log(SDB_LOG_ERR, "core: Cannot configure unknown "
+					"plugin '%s'. Missing 'LoadPlugin \"%s\"'?",
+					name, name);
 		else
 			sdb_log(SDB_LOG_ERR, "core: Plugin '%s' did not register "
 					"a config callback.", name);
@@ -721,12 +1063,72 @@ sdb_plugin_configure(const char *name, oconfig_item_t *ci)
 	}
 
 	old_ctx = ctx_set(plugin->cb_ctx);
-	callback = plugin->cb_callback;
+	callback = (sdb_plugin_config_cb)plugin->cb_callback;
 	status = callback(ci);
 	ctx_set(old_ctx);
 	return status;
 } /* sdb_plugin_configure */
 
+int
+sdb_plugin_reconfigure_init(void)
+{
+	sdb_llist_iter_t *iter;
+
+	iter = sdb_llist_get_iter(config_list);
+	if (config_list && (! iter))
+		return -1;
+
+	/* deconfigure all plugins */
+	while (sdb_llist_iter_has_next(iter)) {
+		callback_t *plugin;
+		sdb_plugin_config_cb callback;
+		ctx_t *old_ctx;
+
+		plugin = CB(sdb_llist_iter_get_next(iter));
+		old_ctx = ctx_set(plugin->cb_ctx);
+		callback = (sdb_plugin_config_cb)plugin->cb_callback;
+		callback(NULL);
+		ctx_set(old_ctx);
+	}
+	sdb_llist_iter_destroy(iter);
+
+	iter = sdb_llist_get_iter(all_plugins);
+	if (all_plugins && (! iter))
+		return -1;
+
+	/* record all plugins as being unused */
+	while (sdb_llist_iter_has_next(iter))
+		CTX(sdb_llist_iter_get_next(iter))->use_cnt = 0;
+	sdb_llist_iter_destroy(iter);
+
+	sdb_plugin_unregister_all();
+	return 0;
+} /* sdb_plugin_reconfigure_init */
+
+int
+sdb_plugin_reconfigure_finish(void)
+{
+	sdb_llist_iter_t *iter;
+
+	iter = sdb_llist_get_iter(all_plugins);
+	if (all_plugins && (! iter))
+		return -1;
+
+	while (sdb_llist_iter_has_next(iter)) {
+		ctx_t *ctx = CTX(sdb_llist_iter_get_next(iter));
+		if (ctx->use_cnt)
+			continue;
+
+		sdb_log(SDB_LOG_INFO, "core: Module %s no longer in use",
+				ctx->info.plugin_name);
+		sdb_llist_iter_remove_current(iter);
+		plugin_unregister_by_name(ctx->info.plugin_name);
+		sdb_object_deref(SDB_OBJ(ctx));
+	}
+	sdb_llist_iter_destroy(iter);
+	return 0;
+} /* sdb_plugin_reconfigure_finish */
+
 int
 sdb_plugin_init_all(void)
 {
@@ -735,29 +1137,61 @@ sdb_plugin_init_all(void)
 
 	iter = sdb_llist_get_iter(init_list);
 	while (sdb_llist_iter_has_next(iter)) {
-		sdb_plugin_cb_t *cb;
+		callback_t *cb;
 		sdb_plugin_init_cb callback;
 		ctx_t *old_ctx;
 
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
-		cb = SDB_PLUGIN_CB(obj);
+		cb = CB(obj);
 
-		callback = cb->cb_callback;
+		callback = (sdb_plugin_init_cb)cb->cb_callback;
 
 		old_ctx = ctx_set(cb->cb_ctx);
 		if (callback(cb->cb_user_data)) {
 			sdb_log(SDB_LOG_ERR, "core: Failed to initialize plugin "
 					"'%s'. Unregistering all callbacks.", obj->name);
+			ctx_set(old_ctx);
 			plugin_unregister_by_name(cb->cb_ctx->info.plugin_name);
 			++ret;
 		}
-		ctx_set(old_ctx);
+		else
+			ctx_set(old_ctx);
 	}
 	sdb_llist_iter_destroy(iter);
 	return ret;
 } /* sdb_plugin_init_all */
 
+int
+sdb_plugin_shutdown_all(void)
+{
+	sdb_llist_iter_t *iter;
+	int ret = 0;
+
+	iter = sdb_llist_get_iter(shutdown_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		callback_t *cb;
+		sdb_plugin_shutdown_cb callback;
+		ctx_t *old_ctx;
+
+		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
+		assert(obj);
+		cb = CB(obj);
+
+		callback = (sdb_plugin_shutdown_cb)cb->cb_callback;
+
+		old_ctx = ctx_set(cb->cb_ctx);
+		if (callback(cb->cb_user_data)) {
+			sdb_log(SDB_LOG_ERR, "core: Failed to shutdown plugin '%s'.",
+					obj->name);
+			++ret;
+		}
+		ctx_set(old_ctx);
+	}
+	sdb_llist_iter_destroy(iter);
+	return ret;
+} /* sdb_plugin_shutdown_all */
+
 int
 sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 {
@@ -780,18 +1214,18 @@ sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 		if (! obj)
 			return -1;
 
-		callback = SDB_PLUGIN_CCB(obj)->ccb_callback;
+		callback = (sdb_plugin_collector_cb)CCB(obj)->ccb_callback;
 
 		if (! (now = sdb_gettime())) {
 			char errbuf[1024];
 			sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
 					"time in collector main loop: %s",
 					sdb_strerror(errno, errbuf, sizeof(errbuf)));
-			now = SDB_PLUGIN_CCB(obj)->ccb_next_update;
+			now = CCB(obj)->ccb_next_update;
 		}
 
-		if (now < SDB_PLUGIN_CCB(obj)->ccb_next_update) {
-			interval = SDB_PLUGIN_CCB(obj)->ccb_next_update - now;
+		if (now < CCB(obj)->ccb_next_update) {
+			interval = CCB(obj)->ccb_next_update - now;
 
 			errno = 0;
 			while (loop->do_loop && sdb_sleep(interval, &interval)) {
@@ -800,22 +1234,30 @@ sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 					sdb_log(SDB_LOG_ERR, "core: Failed to sleep "
 							"in collector main loop: %s",
 							sdb_strerror(errno, errbuf, sizeof(errbuf)));
+					sdb_llist_insert_sorted(collector_list, obj,
+							plugin_cmp_next_update);
+					sdb_object_deref(obj);
 					return -1;
 				}
 				errno = 0;
 			}
 
-			if (! loop->do_loop)
+			if (! loop->do_loop) {
+				/* put back; don't worry about errors */
+				sdb_llist_insert_sorted(collector_list, obj,
+						plugin_cmp_next_update);
+				sdb_object_deref(obj);
 				return 0;
+			}
 		}
 
-		old_ctx = ctx_set(SDB_PLUGIN_CCB(obj)->ccb_ctx);
-		if (callback(SDB_PLUGIN_CCB(obj)->ccb_user_data)) {
+		old_ctx = ctx_set(CCB(obj)->ccb_ctx);
+		if (callback(CCB(obj)->ccb_user_data)) {
 			/* XXX */
 		}
 		ctx_set(old_ctx);
 
-		interval = SDB_PLUGIN_CCB(obj)->ccb_interval;
+		interval = CCB(obj)->ccb_interval;
 		if (! interval)
 			interval = loop->default_interval;
 		if (! interval) {
@@ -826,21 +1268,21 @@ sdb_plugin_collector_loop(sdb_plugin_loop_t *loop)
 			continue;
 		}
 
-		SDB_PLUGIN_CCB(obj)->ccb_next_update += interval;
+		CCB(obj)->ccb_next_update += interval;
 
 		if (! (now = sdb_gettime())) {
 			char errbuf[1024];
 			sdb_log(SDB_LOG_ERR, "core: Failed to determine current "
 					"time in collector main loop: %s",
 					sdb_strerror(errno, errbuf, sizeof(errbuf)));
-			now = SDB_PLUGIN_CCB(obj)->ccb_next_update;
+			now = CCB(obj)->ccb_next_update;
 		}
 
-		if (now > SDB_PLUGIN_CCB(obj)->ccb_next_update) {
+		if (now > CCB(obj)->ccb_next_update) {
 			sdb_log(SDB_LOG_WARNING, "core: Plugin '%s' took too "
 					"long; skipping iterations to keep up.",
 					obj->name);
-			SDB_PLUGIN_CCB(obj)->ccb_next_update = now;
+			CCB(obj)->ccb_next_update = now;
 		}
 
 		if (sdb_llist_insert_sorted(collector_list, obj,
@@ -878,8 +1320,8 @@ sdb_plugin_cname(char *hostname)
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
 
-		callback = SDB_PLUGIN_CB(obj)->cb_callback;
-		cname = callback(hostname, SDB_PLUGIN_CB(obj)->cb_user_data);
+		callback = (sdb_plugin_cname_cb)CB(obj)->cb_callback;
+		cname = callback(hostname, CB(obj)->cb_user_data);
 		if (cname) {
 			free(hostname);
 			hostname = cname;
@@ -896,12 +1338,11 @@ sdb_plugin_log(int prio, const char *msg)
 	sdb_llist_iter_t *iter;
 	int ret = -1;
 
+	bool logged = 0;
+
 	if (! msg)
 		return 0;
 
-	if (! log_list)
-		return fprintf(stderr, "[%s] %s\n", SDB_LOG_PRIO_TO_STRING(prio), msg);
-
 	iter = sdb_llist_get_iter(log_list);
 	while (sdb_llist_iter_has_next(iter)) {
 		sdb_plugin_log_cb callback;
@@ -910,12 +1351,19 @@ sdb_plugin_log(int prio, const char *msg)
 		sdb_object_t *obj = sdb_llist_iter_get_next(iter);
 		assert(obj);
 
-		callback = SDB_PLUGIN_CB(obj)->cb_callback;
-		tmp = callback(prio, msg, SDB_PLUGIN_CB(obj)->cb_user_data);
+		callback = (sdb_plugin_log_cb)CB(obj)->cb_callback;
+		tmp = callback(prio, msg, CB(obj)->cb_user_data);
 		if (tmp > ret)
 			ret = tmp;
+
+		if (CB(obj)->cb_ctx)
+			logged = 1;
+		/* else: this is an internally registered callback */
 	}
 	sdb_llist_iter_destroy(iter);
+
+	if (! logged)
+		return fprintf(stderr, "[%s] %s\n", SDB_LOG_PRIO_TO_STRING(prio), msg);
 	return ret;
 } /* sdb_plugin_log */
 
@@ -960,5 +1408,392 @@ sdb_plugin_logf(int prio, const char *fmt, ...)
 	return ret;
 } /* sdb_plugin_logf */
 
+sdb_timeseries_t *
+sdb_plugin_fetch_timeseries(const char *type, const char *id,
+		sdb_timeseries_opts_t *opts)
+{
+	callback_t *plugin;
+	sdb_plugin_fetch_ts_cb callback;
+	sdb_timeseries_t *ts;
+
+	ctx_t *old_ctx;
+
+	if ((! type) || (! id) || (! opts))
+		return NULL;
+
+	plugin = CB(sdb_llist_search_by_name(ts_fetcher_list, type));
+	if (! plugin) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot fetch time-series of type %s: "
+				"no such plugin loaded", type);
+		errno = ENOENT;
+		return NULL;
+	}
+
+	old_ctx = ctx_set(plugin->cb_ctx);
+	callback = (sdb_plugin_fetch_ts_cb)plugin->cb_callback;
+	ts = callback(id, opts, plugin->cb_user_data);
+	ctx_set(old_ctx);
+	return ts;
+} /* sdb_plugin_fetch_timeseries */
+
+int
+sdb_plugin_query(sdb_ast_node_t *ast,
+		sdb_store_writer_t *w, sdb_object_t *wd, sdb_strbuf_t *errbuf)
+{
+	size_t n = sdb_llist_len(reader_list);
+	reader_t *reader;
+	sdb_object_t *q;
+	int status = 0;
+
+	if (! ast)
+		return 0;
+
+	if ((ast->type != SDB_AST_TYPE_FETCH)
+			&& (ast->type != SDB_AST_TYPE_LIST)
+			&& (ast->type != SDB_AST_TYPE_LOOKUP)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot execute query of type %s",
+				SDB_AST_TYPE_TO_STRING(ast));
+		sdb_strbuf_sprintf(errbuf, "Cannot execute query of type %s",
+				SDB_AST_TYPE_TO_STRING(ast));
+		return -1;
+	}
+
+	if (n != 1) {
+		char *msg = (n > 0)
+			? "Cannot execute query: multiple readers not supported"
+			: "Cannot execute query: no readers registered";
+		sdb_strbuf_sprintf(errbuf, "%s", msg);
+		sdb_log(SDB_LOG_ERR, "core: %s", msg);
+		return -1;
+	}
+
+	reader = READER(sdb_llist_get(reader_list, 0));
+	assert(reader);
+
+	q = reader->impl.prepare_query(ast, errbuf, reader->r_user_data);
+	if (q)
+		status = reader->impl.execute_query(q, w, SDB_OBJ(wd),
+				errbuf, reader->r_user_data);
+	else
+		status = -1;
+
+	sdb_object_deref(SDB_OBJ(q));
+	sdb_object_deref(SDB_OBJ(reader));
+	return status;
+} /* sdb_plugin_query */
+
+int
+sdb_plugin_store_host(const char *name, sdb_time_t last_update)
+{
+	sdb_store_host_t host = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	int status = 0;
+
+	if (! name)
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store host: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(name));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	host.name = cname;
+	host.last_update = last_update;
+	host.backends = (const char * const *)backends;
+	get_backend(backends, &host.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_host(&host, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+	free(cname);
+	return status;
+} /* sdb_plugin_store_host */
+
+int
+sdb_plugin_store_service(const char *hostname, const char *name,
+		sdb_time_t last_update)
+{
+	sdb_store_service_t service = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	sdb_data_t d;
+
+	int status = 0;
+
+	if ((! hostname) || (! name))
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store service: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	service.hostname = cname;
+	service.name = name;
+	service.last_update = last_update;
+	service.backends = (const char * const *)backends;
+	get_backend(backends, &service.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_service(&service, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+
+	if (! status) {
+		/* record the hostname as an attribute */
+		d.type = SDB_TYPE_STRING;
+		d.data.string = cname;
+		if (sdb_plugin_store_service_attribute(cname, name,
+					"hostname", &d, last_update))
+			status = -1;
+	}
+
+	free(cname);
+	return status;
+} /* sdb_plugin_store_service */
+
+int
+sdb_plugin_store_metric(const char *hostname, const char *name,
+		sdb_metric_store_t *store, sdb_time_t last_update)
+{
+	sdb_store_metric_t metric = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	sdb_data_t d;
+
+	int status = 0;
+
+	if ((! hostname) || (! name))
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store metric: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	if (store && ((! store->type) || (! store->id)))
+		store = NULL;
+
+	metric.hostname = cname;
+	metric.name = name;
+	if (store) {
+		metric.store.type = store->type;
+		metric.store.id = store->id;
+	}
+	metric.last_update = last_update;
+	metric.backends = (const char * const *)backends;
+	get_backend(backends, &metric.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_metric(&metric, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+
+	if (! status) {
+		/* record the hostname as an attribute */
+		d.type = SDB_TYPE_STRING;
+		d.data.string = cname;
+		if (sdb_plugin_store_metric_attribute(cname, name,
+					"hostname", &d, last_update))
+			status = -1;
+	}
+
+	free(cname);
+	return status;
+} /* sdb_plugin_store_metric */
+
+int
+sdb_plugin_store_attribute(const char *hostname, const char *key,
+		const sdb_data_t *value, sdb_time_t last_update)
+{
+	sdb_store_attribute_t attr = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	int status = 0;
+
+	if ((! hostname) || (! key) || (! value))
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store attribute: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	attr.parent_type = SDB_HOST;
+	attr.parent = cname;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update;
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+	free(cname);
+	return status;
+} /* sdb_plugin_store_attribute */
+
+int
+sdb_plugin_store_service_attribute(const char *hostname, const char *service,
+		const char *key, const sdb_data_t *value, sdb_time_t last_update)
+{
+	sdb_store_attribute_t attr = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	int status = 0;
+
+	if ((! hostname) || (! service) || (! key) || (! value))
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store service attribute: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	attr.hostname = cname;
+	attr.parent_type = SDB_SERVICE;
+	attr.parent = service;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update;
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+	free(cname);
+	return status;
+} /* sdb_plugin_store_service_attribute */
+
+int
+sdb_plugin_store_metric_attribute(const char *hostname, const char *metric,
+		const char *key, const sdb_data_t *value, sdb_time_t last_update)
+{
+	sdb_store_attribute_t attr = { 0 };
+	char *backends[1];
+	char *cname;
+
+	sdb_llist_iter_t *iter;
+	int status = 0;
+
+	if ((! hostname) || (! metric) || (! key) || (! value))
+		return -1;
+
+	if (! sdb_llist_len(writer_list)) {
+		sdb_log(SDB_LOG_ERR, "core: Cannot store metric attribute: "
+				"no writers registered");
+		return -1;
+	}
+
+	cname = sdb_plugin_cname(strdup(hostname));
+	if (! cname) {
+		sdb_log(SDB_LOG_ERR, "core: strdup failed");
+		return -1;
+	}
+
+	attr.hostname = cname;
+	attr.parent_type = SDB_METRIC;
+	attr.parent = metric;
+	attr.key = key;
+	attr.value = *value;
+	attr.last_update = last_update;
+	attr.backends = (const char * const *)backends;
+	get_backend(backends, &attr.backends_num);
+
+	iter = sdb_llist_get_iter(writer_list);
+	while (sdb_llist_iter_has_next(iter)) {
+		writer_t *writer = WRITER(sdb_llist_iter_get_next(iter));
+		int s;
+		assert(writer);
+		s = writer->impl.store_attribute(&attr, writer->w_user_data);
+		if (((s > 0) && (status >= 0)) || (s < 0))
+			status = s;
+	}
+	sdb_llist_iter_destroy(iter);
+	free(cname);
+	return status;
+} /* sdb_plugin_store_metric_attribute */
+
 /* vim: set tw=78 sw=4 ts=4 noexpandtab : */