audio: change a detail about filter insertion

The af_add() function has a problem: if the inserted filter returns
AF_DETACH during init, the function will have a dangling pointer. Until
now this was avoided by making sure none of the used filters actually
return AF_DETACH, but it's getting infeasible.

Solve this by requiring passing an unique label to af_add(), which is
then used instead of the pointer.

3 files changed, 14 insertions, 10 deletions

diff --git a/audio/filter/af.c b/audio/filter/af.c
index 2889e87bb7..48f6d58868 100644
--- a/audio/filter/af.c
+++ b/audio/filter/af.c
@@ -689,8 +689,14 @@ int af_init(struct af_stream *s)
    to the stream s. The filter will be inserted somewhere nice in the
    list of filters. The return value is a pointer to the new filter,
    If the filter couldn't be added the return value is NULL. */
-struct af_instance *af_add(struct af_stream *s, char *name, char **args)
+struct af_instance *af_add(struct af_stream *s, char *name, char *label,
+                           char **args)
 {
+    assert(label);
+
+    if (af_find_by_label(s, label))
+        return NULL;
+
     struct af_instance *new;
     // Insert the filter somewhere nice
     if (af_is_conversion_filter(s->first->next))
@@ -699,17 +705,14 @@ struct af_instance *af_add(struct af_stream *s, char *name, char **args)
         new = af_prepend(s, s->first->next, name, args);
     if (!new)
         return NULL;
+    new->label = talloc_strdup(new, label);
 
     // Reinitalize the filter list
     if (af_reinit(s) != AF_OK) {
-        af_remove(s, new);
-        if (af_reinit(s) != AF_OK) {
-            af_uninit(s);
-            af_init(s);
-        }
+        af_remove_by_label(s, label);
         return NULL;
     }
-    return new;
+    return af_find_by_label(s, label);
 }
 
 struct af_instance *af_find_by_label(struct af_stream *s, char *label)
diff --git a/audio/filter/af.h b/audio/filter/af.h
index 4c67208123..65a30f7dd1 100644
--- a/audio/filter/af.h
+++ b/audio/filter/af.h
@@ -141,7 +141,8 @@ struct af_stream *af_new(struct mpv_global *global);
 void af_destroy(struct af_stream *s);
 int af_init(struct af_stream *s);
 void af_uninit(struct af_stream *s);
-struct af_instance *af_add(struct af_stream *s, char *name, char **args);
+struct af_instance *af_add(struct af_stream *s, char *name, char *label,
+                           char **args);
 int af_remove_by_label(struct af_stream *s, char *label);
 struct af_instance *af_find_by_label(struct af_stream *s, char *label);
 struct af_instance *af_control_any_rev(struct af_stream *s, int cmd, void *arg);
diff --git a/audio/mixer.c b/audio/mixer.c
index 0eb9c86453..7ae7ed458d 100644
--- a/audio/mixer.c
+++ b/audio/mixer.c
@@ -135,7 +135,7 @@ static void setvolume_internal(struct mixer *mixer, float l, float r)
         if (gain == 1.0)
             return;
         MP_VERBOSE(mixer, "Inserting volume filter.\n");
-        if (!(af_add(mixer->af, "volume", NULL)
+        if (!(af_add(mixer->af, "volume", "softvol", NULL)
               && af_control_any_rev(mixer->af, AF_CONTROL_SET_VOLUME, &gain)))
             MP_ERR(mixer, "No volume control available.\n");
     }
@@ -222,7 +222,7 @@ void mixer_setbalance(struct mixer *mixer, float val)
     if (val == 0)
         return;
 
-    if (!(af_pan_balance = af_add(mixer->af, "pan", NULL))) {
+    if (!(af_pan_balance = af_add(mixer->af, "pan", "autopan", NULL))) {
         MP_ERR(mixer, "No balance control available.\n");
         return;
     }