Add usage reference count for tracepoints

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

diff --git a/liblttng-ust/tracepoint.c b/liblttng-ust/tracepoint.c
index e68ca58be07ff59703e7fa4ead0f2627587ca9b9..8c137a3892a99558d26ce4066db1c341e87639a4 100644 (file)
--- a/liblttng-ust/tracepoint.c
+++ b/liblttng-ust/tracepoint.c
@@ -95,6 +95,7 @@ struct tracepoint_entry {
        struct cds_hlist_node hlist;
        struct tracepoint_probe *probes;
        int refcount;   /* Number of times armed. 0 if disarmed. */
+       int callsite_refcount;  /* how many libs use this tracepoint */
        const char *signature;
        char name[0];
 };
@@ -295,6 +296,7 @@ static struct tracepoint_entry *add_tracepoint(const char *name,
        e->name[name_len] = '\0';
        e->probes = NULL;
        e->refcount = 0;
+       e->callsite_refcount = 0;
        e->signature = signature;
        cds_hlist_add_head(&e->hlist, head);
        return e;
@@ -369,6 +371,7 @@ static void add_callsite(struct tracepoint_lib * lib, struct tracepoint *tp)
        const char *name = tp->name;
        size_t name_len = strlen(name);
        uint32_t hash;
+       struct tracepoint_entry *tp_entry;
 
        if (name_len > LTTNG_UST_SYM_NAME_LEN - 1) {
                WARN("Truncating tracepoint name %s which exceeds size limits of %u chars", name, LTTNG_UST_SYM_NAME_LEN - 1);
@@ -381,6 +384,11 @@ static void add_callsite(struct tracepoint_lib * lib, struct tracepoint *tp)
        cds_hlist_add_head(&e->hlist, head);
        e->tp = tp;
        cds_list_add(&e->node, &lib->callsites);
+
+       tp_entry = get_tracepoint(name);
+       if (!tp_entry)
+               return;
+       tp_entry->callsite_refcount++;
 }
 
 /*
@@ -389,6 +397,14 @@ static void add_callsite(struct tracepoint_lib * lib, struct tracepoint *tp)
  */
 static void remove_callsite(struct callsite_entry *e)
 {
+       struct tracepoint_entry *tp_entry;
+
+       tp_entry = get_tracepoint(e->tp->name);
+       if (tp_entry) {
+               tp_entry->callsite_refcount--;
+               if (tp_entry->callsite_refcount == 0)
+                       disable_tracepoint(e->tp);
+       }
        cds_hlist_del(&e->hlist);
        cds_list_del(&e->node);
        free(e);
@@ -705,24 +721,6 @@ static void new_tracepoints(struct tracepoint * const *start, struct tracepoint
        }
 }
 
-static
-void lib_disable_tracepoints(struct tracepoint_lib *lib)
-{
-       struct tracepoint * const *begin;
-       struct tracepoint * const *end;
-       struct tracepoint * const *iter;
-
-       begin = lib->tracepoints_start;
-       end = lib->tracepoints_start + lib->tracepoints_count;
-
-       for (iter = begin; iter < end; iter++) {
-               if (!*iter)
-                       continue;       /* skip dummy */
-               disable_tracepoint(*iter);
-       }
-
-}
-
 int tracepoint_register_lib(struct tracepoint * const *tracepoints_start,
                            int tracepoints_count)
 {
@@ -780,13 +778,11 @@ int tracepoint_unregister_lib(struct tracepoint * const *tracepoints_start)
 
                cds_list_del(&lib->list);
                /*
-                * Force tracepoint disarm for all tracepoints of this lib.
-                * This takes care of destructor of library that would leave a
-                * LD_PRELOAD wrapper override function enabled for tracing, but
-                * the session teardown would not be able to reach the
-                * tracepoint anymore to disable it.
+                * Unregistering a callsite also decreases the
+                * callsite reference count of the corresponding
+                * tracepoint, and disables the tracepoint if
+                * the reference count drops to zero.
                 */
-               lib_disable_tracepoints(lib);
                lib_unregister_callsites(lib);
                DBG("just unregistered a tracepoints section from %p",
                        lib->tracepoints_start);