Merge branch 't/writer_cleanups'

diff --combined write_common.c
index 7131a94042dae3b989a73ee5a1b8cd4c84bf2b02,be7f9c221f5bda21b5b7cb79db02ec8f748a3102..04db8ff0d1e0da00207930e682fddc84678e88d2
--- 1/write_common.c
--- 2/write_common.c
+++ b/write_common.c
@@@ -66,27 -66,32 +66,32 @@@ void *check_writer_arg(const char *wa, 
                c = wa[len];
                if (c && c != ' ')
                        continue;
-               if (c && !writers[i].parse_config)
-                       return NULL;
                *writer_num = i;
-               return writers[i].parse_config(c? wa + len + 1 : "");
+               return writers[i].parse_config_or_die(c? wa + len + 1 : "");
        }
        PARA_ERROR_LOG("writer not found\n");
        return NULL;
  }
  
+ /**
+  * Open a writer node and register the corresponding task.
+  *
+  * \param wn The writer node to open.
+  * \param parent The parent btr node (the source for the writer node).
+  *
+  * The configuration of the writer node stored in \p wn->conf must be
+  * initialized before this function may be called.
+  */
  void register_writer_node(struct writer_node *wn, struct btr_node *parent)
  {
        struct writer *w = writers + wn->writer_num;
        char *name = make_message("%s writer", writer_names[wn->writer_num]);
-       int ret;
  
        wn->btrn = btr_new_node(&(struct btr_node_description)
                EMBRACE(.name = name, .parent = parent,
                .handler = w->execute, .context = wn));
        strcpy(wn->task.status, name);
        free(name);
-       ret = w->open(wn);
        wn->task.post_select = w->post_select;
        wn->task.pre_select = w->pre_select;
        register_task(&wn->task);
@@@ -115,7 -120,7 +120,7 @@@ int setup_writer_node(const char *arg, 
                wn->conf = check_writer_arg(arg, &wn->writer_num);
        else {
                wn->writer_num = DEFAULT_WRITER;
-               wn->conf = writers[DEFAULT_WRITER].parse_config("");
+               wn->conf = writers[DEFAULT_WRITER].parse_config_or_die("");
        }
        if (!wn->conf)
                return -E_WRITE_COMMON_SYNTAX;
@@@ -123,7 -128,6 +128,6 @@@
        return 1;
  }
  
- 
  /**
   * Print the help text of all writers to stdout.
   *
@@@ -153,15 -157,7 +157,15 @@@ static void get_btr_value(struct btr_no
        char *buf = NULL;
        int ret = btr_exec_up(btrn, cmd, &buf);
  
 -      assert(ret >= 0);
 +      if (ret < 0) {
 +              /*
 +               * This really should not happen. It means one of our parent
 +               * nodes died unexpectedly. Proceed with fingers crossed.
 +               */
 +              PARA_CRIT_LOG("cmd %s: %s\n", cmd, para_strerror(-ret));
 +              *result = 0;
 +              return;
 +      }
        ret = para_atoi32(buf, result);
        assert(ret >= 0);
        free(buf);