weston-log: Add 'destroy_subscription' callback for the subscription

As 'new_subscription' can create additional objects, 'destroy_subscription'
will be needed when cleaning up.

As this requires a libweston_major bump (noticed by @pq), bump it up to
8.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Suggested-by: Daniel Stone <daniel.stone@collabora.com>

libweston/backend-drm/drm.c

@@ -3408,7 +3408,7 @@ drm_backend_create(struct weston_compositor *compositor,
 	b->debug = weston_compositor_add_log_scope(compositor->weston_log_ctx,
 						   "drm-backend",
 						   "Debug messages from DRM/KMS backend\n",
-						    NULL, NULL);
+						    NULL, NULL, NULL);
 
 	compositor->backend = &b->base;
 

libweston/compositor.c

@@ -7309,7 +7309,7 @@ weston_compositor_create(struct wl_display *display,
 	ec->debug_scene =
 		weston_compositor_add_log_scope(ec->weston_log_ctx, "scene-graph",
 						"Scene graph details\n",
-						debug_scene_graph_cb,
+						debug_scene_graph_cb, NULL,
 						ec);
 
 	return ec;

libweston/content-protection.c

@@ -343,6 +343,6 @@ weston_compositor_enable_content_protection(struct weston_compositor *compositor
 	cp->debug = weston_compositor_add_log_scope(compositor->weston_log_ctx,
 						    "content-protection-debug",
 						    "debug-logs for content-protection",
-						    NULL, NULL);
+						    NULL, NULL, NULL);
 	return 0;
 }

libweston/weston-log.c

@@ -82,6 +82,7 @@ struct weston_log_scope {
 	char *name;
 	char *desc;
 	weston_log_scope_cb new_subscription;
+	weston_log_scope_cb destroy_subscription;
 	void *user_data;
 	struct wl_list compositor_link;
 	struct wl_list subscription_list;  /**< weston_log_subscription::source_link */
@@ -260,6 +261,10 @@ void
 weston_log_subscription_destroy(struct weston_log_subscription *sub)
 {
 	assert(sub);
+
+	if (sub->source->destroy_subscription)
+		sub->source->destroy_subscription(sub, sub->source->user_data);
+
 	if (sub->owner)
 		wl_list_remove(&sub->owner_link);
 
@@ -518,6 +523,8 @@ weston_compositor_is_debug_protocol_enabled(struct weston_compositor *wc)
  * @param description The log scope description for humans; must not be NULL.
  * @param new_subscription Optional callback when a client subscribes to this
  * scope.
+ * @param destroy_subscription Optional callback when a client destroys the
+ * subscription.
  * @param user_data Optional user data pointer for the callback.
  * @returns A valid pointer on success, NULL on failure.
  *
@@ -561,6 +568,7 @@ weston_compositor_add_log_scope(struct weston_log_context *log_ctx,
 				const char *name,
 				const char *description,
 				weston_log_scope_cb new_subscription,
+				weston_log_scope_cb destroy_subscription,
 				void *user_data)
 {
 	struct weston_log_scope *scope;
@@ -593,6 +601,7 @@ weston_compositor_add_log_scope(struct weston_log_context *log_ctx,
 	scope->name = strdup(name);
 	scope->desc = strdup(description);
 	scope->new_subscription = new_subscription;
+	scope->destroy_subscription = destroy_subscription;
 	scope->user_data = user_data;
 	wl_list_init(&scope->subscription_list);