Both undo options print messages now. Undo Load State can now also be

undone ad infinitum. Doing it in succession swaps the current state for
the backed up state.

command.c

@@ -1601,8 +1601,14 @@ static void command_event_undo_save_state(char *s, size_t len)
    {
       snprintf(s, len, "%s \"%s\".",
             msg_hash_to_str(MSG_FAILED_TO_UNDO_SAVE_STATE),
-            "from internal buffer");
+            "RAM");
+
+      return;
    }
+
+   /* TODO/FIXME - use msg_hash_to_str here and there */
+   snprintf(s, len, "%s",
+            "Restored save state.");
 }
 
 /**
@@ -1639,8 +1645,12 @@ static void command_event_undo_load_state(char *s, size_t len)
    {
       snprintf(s, len, "%s \"%s\".",
             msg_hash_to_str(MSG_FAILED_TO_UNDO_LOAD_STATE),
-            "from internal buffer");
+            "RAM");
+      return;
    }
+   /* TODO/FIXME - use msg_hash_to_str here and there */
+   snprintf(s, len, "%s",
+            "Undid load state.");  
 }
 
 static void command_event_main_state(unsigned cmd)

command.h

@@ -49,6 +49,7 @@ enum event_command
    CMD_EVENT_UNLOAD_CORE,
    CMD_EVENT_LOAD_STATE,
    CMD_EVENT_UNDO_LOAD_STATE,
+   /* Rewrites a savestate on disk */
    CMD_EVENT_UNDO_SAVE_STATE,
    CMD_EVENT_SAVE_STATE,
    CMD_EVENT_SAVE_STATE_DECREMENT,

content.h

@@ -47,7 +47,7 @@ bool content_save_ram_file(unsigned slot);
 
 /* Load a state from disk to memory. */
 bool content_load_state(const char* path);
-bool content_load_state_with_backup(const char* path, bool save_to_backup_buffer);
+bool content_load_state_with_backup(const char* path, bool load_to_backup_buffer);
 
 /* Save a state from memory to disk. */
 bool content_save_state(const char *path);
@@ -78,6 +78,9 @@ void content_deinit(void);
  * selected libretro core. */
 bool content_init(void);
 
+/* Resets the state and savefile backup buffers */
+bool content_reset_savestate_backups();
+
 RETRO_END_DECLS
 
 #endif

tasks/task_save_state.c

@@ -64,7 +64,7 @@ struct sram_block
 
 bool content_undo_load_state()
 {
-   if (old_state_buf.data == NULL)
+   if (old_state_buf.data == NULL || old_state_buf.size == 0)
       return false;
 
    unsigned i;
@@ -79,7 +79,7 @@ bool content_undo_load_state()
 
    RARCH_LOG("%s: \"%s\".\n",
          msg_hash_to_str(MSG_LOADING_STATE),
-         "from internal buffer");
+         "RAM");
 
    RARCH_LOG("%s: %u %s.\n",
          msg_hash_to_str(MSG_STATE_SIZE),
@@ -136,11 +136,25 @@ bool content_undo_load_state()
             memcpy(blocks[i].data, ptr, blocks[i].size);
       }
    }
+
+   /* We need to make a temporary copy of the buffer, to allow the swap below */
+   void* temp_data = malloc(old_state_buf.size);
+   size_t temp_data_size = old_state_buf.size;
+   memcpy(temp_data, old_state_buf.data, old_state_buf.size);
+
+   serial_info.data_const = temp_data;
+   serial_info.size       = temp_data_size;
 
-   serial_info.data_const = old_state_buf.data;
-   serial_info.size       = old_state_buf.size;
+   /* Swap the current state with the backup state. This way, we can undo
+   what we're undoing */
+   content_save_state_with_backup("RAM", false);
    bool ret               = core_unserialize(&serial_info);
 
+   /* Clean up the temporary copy */
+   free(temp_data);
+   temp_data = NULL;
+   temp_data_size = 0;
+
    /* Flush back. */
    for (i = 0; i < num_blocks; i++)
    {
@@ -166,16 +180,7 @@ bool content_undo_load_state()
    if (!ret)   
       RARCH_ERR("%s \"%s\".\n",
          msg_hash_to_str(MSG_FAILED_TO_UNDO_LOAD_STATE),
-         "from internal buffer");
-
-   /* Wipe the old state buffer, it's meant to be one use only */
-   old_state_buf.path[0] = '\0';
-   if (old_state_buf.data) {
-      free(old_state_buf.data);
-      old_state_buf.data = NULL;
-   }
-
-   old_state_buf.data = 0;
+         "RAM");
 
    return ret;
 }
@@ -196,7 +201,7 @@ bool content_undo_save_state()
    if (!ret)   
       RARCH_ERR("%s \"%s\".\n",
          msg_hash_to_str(MSG_FAILED_TO_UNDO_SAVE_STATE),
-         "from internal buffer");
+         "RAM");
 
    return ret;
 }
@@ -388,7 +393,7 @@ bool content_load_state_with_backup(const char *path, bool load_to_backup_buffer
    serial_info.size       = size;
 
    /* Backup the current state so we can undo this load */
-   content_save_state_with_backup("internal buffer", false);
+   content_save_state_with_backup("RAM", false);
    ret                    = core_unserialize(&serial_info);
 
    /* Flush back. */
@@ -443,12 +448,14 @@ bool content_rename_state(const char *origin, const char *dest)
 }
 
 /*
-* Resets the state and savefile backups
+* 
 * TODO/FIXME: Figure out when and where this should be called
 *
 */
 bool content_reset_savestate_backups()
 {
+   printf("Resetting undo buffers.\n");
+
    if (old_save_file.data)
    {
       free(old_save_file.data);