options: simplify somewhat by introducing a union for option values

The m_option_value union is supposed to contain a field for each
possible option type (as long as it actually stores data). This helps
avoiding silly temporary memory alocations. Using a pointer to an union
and to a field of the union interchangeably should be allowed by
standard C.

3 files changed, 30 insertions, 20 deletions

diff --git a/m_config.c b/m_config.c
index ae7f528060..11272766d2 100644
--- a/m_config.c
+++ b/m_config.c
@@ -334,15 +334,14 @@ static void m_config_add_option(struct m_config *config,
             } else if (arg->type->flags & M_OPT_TYPE_DYNAMIC) {
                 // Initialize dynamically managed fields from static data (like
                 // string options): copy the option into temporary memory,
-                // clear the original option (to void m_option freeing the
+                // clear the original option (to stop m_option from freeing the
                 // static data), copy it back.
                 if (co->data) {
-                    void *temp = talloc_zero_size(NULL, arg->type->size);
-                    m_option_copy(arg, temp, co->data);
+                    union m_option_value temp = {0};
+                    m_option_copy(arg, &temp, co->data);
                     memset(co->data, 0, arg->type->size);
-                    m_option_copy(arg, co->data, temp);
-                    m_option_free(arg, temp);
-                    talloc_free(temp);
+                    m_option_copy(arg, co->data, &temp);
+                    m_option_free(arg, &temp);
                 }
             }
         }
diff --git a/m_option.h b/m_option.h
index f05fe17bd4..2bd9054ac2 100644
--- a/m_option.h
+++ b/m_option.h
@@ -178,6 +178,25 @@ struct m_sub_options {
 #define CONF_TYPE_TIME          (&m_option_type_time)
 #define CONF_TYPE_TIME_SIZE     (&m_option_type_time_size)
 
+// Possible option values. Code is allowed to access option data without going
+// through this union. It serves for self-documentation and to get minimal
+// size/alignment requirements for option values in general.
+union m_option_value {
+    int flag; // not the C type "bool"!
+    int int_;
+    int64_t int64;
+    float float_;
+    double double_;
+    char *string;
+    char **string_list;
+    int imgfmt;
+    int afmt;
+    m_span_t span;
+    m_obj_settings_t *obj_settings_list;
+    double time;
+    m_time_size_t time_size;
+};
+
 ////////////////////////////////////////////////////////////////////////////
 
 // Option type description
diff --git a/m_property.c b/m_property.c
index e75cbe43ac..ac68d86163 100644
--- a/m_property.c
+++ b/m_property.c
@@ -69,7 +69,7 @@ int m_property_do(const m_option_t *prop_list, const char *name,
                   int action, void *arg, void *ctx)
 {
     const m_option_t *opt;
-    void *val;
+    union m_option_value val = {0};
     int r;
 
     switch (action) {
@@ -85,15 +85,11 @@ int m_property_do(const m_option_t *prop_list, const char *name,
         if ((r =
              do_action(prop_list, name, M_PROPERTY_GET_TYPE, &opt, ctx)) <= 0)
             return r;
-        val = calloc(1, opt->type->size);
-        if ((r = do_action(prop_list, name, M_PROPERTY_GET, val, ctx)) <= 0) {
-            free(val);
+        if ((r = do_action(prop_list, name, M_PROPERTY_GET, &val, ctx)) <= 0)
             return r;
-        }
         if (!arg)
             return M_PROPERTY_ERROR;
-        char *str = m_option_print(opt, val);
-        free(val);
+        char *str = m_option_print(opt, &val);
         *(char **)arg = str;
         return str != NULL;
     case M_PROPERTY_PARSE:
@@ -107,14 +103,10 @@ int m_property_do(const m_option_t *prop_list, const char *name,
             return r;
         if (!arg)
             return M_PROPERTY_ERROR;
-        val = calloc(1, opt->type->size);
-        if ((r = m_option_parse(opt, bstr0(opt->name), bstr0(arg), val)) <= 0) {
-            free(val);
+        if ((r = m_option_parse(opt, bstr0(opt->name), bstr0(arg), &val)) <= 0)
             return r;
-        }
-        r = do_action(prop_list, name, M_PROPERTY_SET, val, ctx);
-        m_option_free(opt, val);
-        free(val);
+        r = do_action(prop_list, name, M_PROPERTY_SET, &val, ctx);
+        m_option_free(opt, &val);
         return r;
     }
     return do_action(prop_list, name, action, arg, ctx);