job-ingest: add module parameter to allow root jobs

Problem: Jobs submitted as root are rejected by the job-ingest module
if the instance owner is not also root, but some tests may need to
simulate submission of jobs to an instance running as root.

Add a job-ingest module parameter `allow-root-jobs`, which disables
the check for uid=0 when used.

Author: grondo

src/modules/job-ingest/job-ingest.c

@@ -82,6 +82,12 @@ static const double batch_timeout = 0.01;
  */
 static int max_fluid_generator_id = 16384 - 16 - 1;
 
+/* By default, root (userid=0) jobs are rejected at submission
+ * unless the instance owner is also root. However, for testing
+ * purposes it may be useful to allow root jobs:
+ */
+static bool allow_root_jobs = false;
+
 struct job_ingest_ctx {
     flux_t *h;
     struct pipeline *pipeline;
@@ -579,7 +585,7 @@ static void submit_cb (flux_t *h, flux_msg_handler_t *mh,
     /* Do not allow root user to submit jobs in a multi-user instance.
      * The jobs will fail at runtime anyway.
      */
-    if (ctx->owner != 0 && job->cred.userid == 0) {
+    if (ctx->owner != 0 && !allow_root_jobs && job->cred.userid == 0) {
         errmsg = "submission of jobs as user root not supported";
         goto error;
     }
@@ -703,6 +709,9 @@ static int job_ingest_configure (struct job_ingest_ctx *ctx,
         else if (strstarts (argv[i], "max-fluid-generator-id=")) {
             max_fluid_id = argv[i] + 23;
         }
+        else if (streq (argv[i], "allow-root-jobs")) {
+            allow_root_jobs = true;
+        }
         else {
             errprintf (error, "Invalid option: %s", argv[i]);
             errno = EINVAL;