m_config: add some convenience functions

To be used by the following commits.

options/m_config.c

@@ -1143,6 +1143,27 @@ void m_config_notify_change_co(struct m_config *config,
         mp_msg_update_msglevels(config->global);
 }
 
+void *mp_get_config_group(void *ta_parent, struct mpv_global *global,
+                          const struct m_sub_options *group)
+{
+    assert(ta_parent); // without you'd necessarily leak memory
+    struct m_config_cache *cache = m_config_cache_alloc(ta_parent, global, group);
+    return cache->opts;
+}
+
+void mp_read_option_raw(struct mpv_global *global, const char *name,
+                        const struct m_option_type *type, void *dst)
+{
+    struct m_config_shadow *shadow = global->config;
+    struct m_config_option *co = m_config_get_co(shadow->root, bstr0(name));
+    assert(co);
+    assert(co->shadow_offset >= 0);
+    assert(co->opt->type == type);
+
+    memset(dst, 0, co->opt->type->size);
+    m_option_copy(co->opt, dst, shadow->data + co->shadow_offset);
+}
+
 struct m_config *mp_get_root_config(struct mpv_global *global)
 {
     return global->config->root;

options/m_config.h

@@ -304,6 +304,20 @@ struct m_config_cache *m_config_cache_alloc(void *ta_parent,
 // data itself will (e.g. string options might be reallocated).
 bool m_config_cache_update(struct m_config_cache *cache);
 
+// Like m_config_cache_alloc(), but return the struct (m_config_cache->opts)
+// directly, with no way to update the config.
+// Warning: does currently not set the child as its own talloc root, which
+//          means the only way to free the struct is by freeing ta_parent.
+void *mp_get_config_group(void *ta_parent, struct mpv_global *global,
+                          const struct m_sub_options *group);
+
+
+// Read a single global option in a thread-safe way. For multiple options,
+// use m_config_cache. The option must exist and match the provided type (the
+// type is used as a sanity check only). Performs semi-expensive lookup.
+void mp_read_option_raw(struct mpv_global *global, const char *name,
+                        const struct m_option_type *type, void *dst);
+
 struct m_config *mp_get_root_config(struct mpv_global *global);
 
 #endif /* MPLAYER_M_CONFIG_H */