qmanager: unpack free ranks in hello and pack into scheduling key

Problem: the sched.hello RPC now includes a `free` key whose value is an
idset of previously partially released ranks. Currently Fluxion doesn't
unpack the key and handle the previously freed resources. The
rv1_noexec doesn't need the freed ranks idset because core only sends
the R that is still allocated in R_lite. However, core doesn't support
processing JGF, so rv1 with the scheduling key contains R with a
scheduling key JGF representing the initial resource set. This leads to
state divergence between core and sched for the rv1 or reader.

Add support for unpacking the `free` key and packing it into the JSON
`scheduling` payload for queue reconstruction and update allocate with
JGF.

qmanager/modules/qmanager_callbacks.cpp

@@ -150,15 +150,21 @@ int qmanager_cb_t::jobmanager_hello_cb (flux_t *h, const flux_msg_t *msg, const
     unsigned int prio;
     uint32_t uid;
     double ts;
+    const char *free_ranks = NULL;
     json_t *jobspec = NULL;
     flux_future_t *f = NULL;
+    json_t *R_jsontmp = NULL;
+    json_t *free_ranks_j = NULL;
+    json_t *sched = NULL;
+    json_error_t json_err;
+    const char *R_final = NULL;
 
     /* Don't expect jobspec to be set here as it is not currently defined
      * in RFC 27.  However, add it anyway in case the hello protocol
      * evolves to include it.  If it is not set, it must be looked up.
      */
     if (flux_msg_unpack (msg,
-                         "{s:I s:i s:i s:f s?o}",
+                         "{s:I s:i s:i s:f s?s s?o}",
                          "id",
                          &id,
                          "priority",
@@ -167,6 +173,8 @@ int qmanager_cb_t::jobmanager_hello_cb (flux_t *h, const flux_msg_t *msg, const
                          &uid,
                          "t_submit",
                          &ts,
+                         "free",
+                         &free_ranks,
                          "jobspec",
                          &jobspec)
         < 0) {
@@ -199,9 +207,34 @@ int qmanager_cb_t::jobmanager_hello_cb (flux_t *h, const flux_msg_t *msg, const
                   queue_name.c_str ());
         goto out;
     }
+    // if free ranks is populated, insert the free ranks into the scheduling key
+    if (free_ranks) {
+        if (!(R_jsontmp = json_loads (R, 0, &json_err))) {
+            errno = ENOMEM;
+            flux_log (h, LOG_ERR, "%s: json_loads", __FUNCTION__);
+            goto out;
+        }
+        if ((sched = json_object_get (R_jsontmp, "scheduling")) == NULL) {
+            R_final = R;
+        } else {
+            free_ranks_j = json_string (free_ranks);
+            json_object_set (sched, "free_ranks", free_ranks_j);
+            if (!(R_final = json_dumps (R_jsontmp, JSON_COMPACT))) {
+                errno = ENOMEM;
+                flux_log (h, LOG_ERR, "%s: json_dumps", __FUNCTION__);
+                goto out;
+            }
+        }
+    } else {
+        R_final = R;
+    }
     queue = ctx->queues.at (queue_name);
-    running_job =
-        std::make_shared<job_t> (job_state_kind_t::RUNNING, id, uid, calc_priority (prio), ts, R);
+    running_job = std::make_shared<job_t> (job_state_kind_t::RUNNING,
+                                           id,
+                                           uid,
+                                           calc_priority (prio),
+                                           ts,
+                                           R_final);
 
     if (queue->reconstruct (static_cast<void *> (h), running_job, R_out) < 0) {
         flux_log_error (h,