Lazy provider registration

[lttng-ust.git] / liblttng-ust / lttng-probes.c

diff --git a/liblttng-ust/lttng-probes.c b/liblttng-ust/lttng-probes.c
index ecf28646e26e768c6f7182d8b42c26ae842ef79a..b1d5fe28558433209f70460119125ca81b433793 100644 (file)
--- a/liblttng-ust/lttng-probes.c
+++ b/liblttng-ust/lttng-probes.c
@@ -40,25 +40,21 @@
  */
 static CDS_LIST_HEAD(_probe_list);
 
-struct cds_list_head *lttng_get_probe_list_head(void)
-{
-       return &_probe_list;
-}
-
-static
-const struct lttng_probe_desc *find_provider(const char *provider)
-{
-       struct lttng_probe_desc *iter;
-       struct cds_list_head *probe_list;
+/*
+ * List of probes registered by not yet processed.
+ */
+static CDS_LIST_HEAD(lazy_probe_init);
 
-       probe_list = lttng_get_probe_list_head();
-       cds_list_for_each_entry(iter, probe_list, head) {
-               if (!strcmp(iter->provider, provider))
-                       return iter;
-       }
-       return NULL;
-}
+/*
+ * lazy_nesting counter ensures we don't trigger lazy probe registration
+ * fixup while we are performing the fixup. It is protected by the ust
+ * mutex.
+ */
+static int lazy_nesting;
 
+/*
+ * Called under ust lock.
+ */
 static
 int check_event_provider(struct lttng_probe_desc *desc)
 {
@@ -76,22 +72,15 @@ int check_event_provider(struct lttng_probe_desc *desc)
        return 1;
 }
 
-int lttng_probe_register(struct lttng_probe_desc *desc)
+/*
+ * Called under ust lock.
+ */
+static
+void lttng_lazy_probe_register(struct lttng_probe_desc *desc)
 {
        struct lttng_probe_desc *iter;
-       int ret = 0;
-       int i;
        struct cds_list_head *probe_list;
-
-       ust_lock();
-
-       /*
-        * Check if the provider has already been registered.
-        */
-       if (find_provider(desc->provider)) {
-               ret = -EEXIST;
-               goto end;
-       }
+       int i;
 
        /*
         * Each provider enforce that every event name begins with the
@@ -111,7 +100,7 @@ int lttng_probe_register(struct lttng_probe_desc *desc)
         * We sort the providers by struct lttng_probe_desc pointer
         * address.
         */
-       probe_list = lttng_get_probe_list_head();
+       probe_list = &_probe_list;
        cds_list_for_each_entry_reverse(iter, probe_list, head) {
                BUG_ON(iter == desc); /* Should never be in the list twice */
                if (iter < desc) {
@@ -130,6 +119,7 @@ desc_added:
         */
        for (i = 0; i < desc->nr_events; i++) {
                const struct lttng_event_desc *ed;
+               int ret;
 
                ed = desc->event_desc[i];
                DBG("Registered event probe \"%s\" with signature \"%s\"",
@@ -137,6 +127,74 @@ desc_added:
                ret = lttng_fix_pending_event_desc(ed);
                assert(!ret);
        }
+}
+
+/*
+ * Called under ust lock.
+ */
+static
+void fixup_lazy_probes(void)
+{
+       struct lttng_probe_desc *iter, *tmp;
+
+       lazy_nesting++;
+       cds_list_for_each_entry_safe(iter, tmp,
+                       &lazy_probe_init, lazy_init_head) {
+               lttng_lazy_probe_register(iter);
+               iter->lazy = 0;
+               cds_list_del(&iter->lazy_init_head);
+       }
+       lazy_nesting--;
+}
+
+/*
+ * Called under ust lock.
+ */
+struct cds_list_head *lttng_get_probe_list_head(void)
+{
+       if (!lazy_nesting && !cds_list_empty(&lazy_probe_init))
+               fixup_lazy_probes();
+       return &_probe_list;
+}
+
+static
+const struct lttng_probe_desc *find_provider(const char *provider)
+{
+       struct lttng_probe_desc *iter;
+       struct cds_list_head *probe_list;
+
+       probe_list = lttng_get_probe_list_head();
+       cds_list_for_each_entry(iter, probe_list, head) {
+               if (!strcmp(iter->provider, provider))
+                       return iter;
+       }
+       return NULL;
+}
+
+int lttng_probe_register(struct lttng_probe_desc *desc)
+{
+       int ret = 0;
+
+       ust_lock();
+
+       /*
+        * Check if the provider has already been registered.
+        */
+       if (find_provider(desc->provider)) {
+               ret = -EEXIST;
+               goto end;
+       }
+       cds_list_add(&desc->lazy_init_head, &lazy_probe_init);
+       desc->lazy = 1;
+       DBG("adding probe %s containing %u events to lazy registration list",
+               desc->provider, desc->nr_events);
+       /*
+        * If there is at least one active session, we need to register
+        * the probe immediately, since we cannot delay event
+        * registration because they are needed ASAP.
+        */
+       if (lttng_session_active())
+               fixup_lazy_probes();
 end:
        ust_unlock();
        return ret;
@@ -151,7 +209,10 @@ int ltt_probe_register(struct lttng_probe_desc *desc)
 void lttng_probe_unregister(struct lttng_probe_desc *desc)
 {
        ust_lock();
-       cds_list_del(&desc->head);
+       if (!desc->lazy)
+               cds_list_del(&desc->head);
+       else
+               cds_list_del(&desc->lazy_init_head);
        DBG("just unregistered probe %s", desc->provider);
        ust_unlock();
 }