From 740d8b0d4b70bb1d6a3c3e73531991d98e1c216b Mon Sep 17 00:00:00 2001
From: Rodrigo Arias <rodrigo.arias@bsc.es>
Date: Tue, 21 Mar 2023 16:55:59 +0100
Subject: [PATCH] Only allow one rank per host in ovnisync

---
 src/emu/ovnisync.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/src/emu/ovnisync.c b/src/emu/ovnisync.c
index a129362..ef58ce1 100644
--- a/src/emu/ovnisync.c
+++ b/src/emu/ovnisync.c
@@ -368,6 +368,27 @@ print_drift_row(FILE *out, struct offset_table *table)
 static void
 print_table_detailed(FILE *out, struct offset_table *table)
 {
+	int fail = 0;
+
+	/* Ensure each hostname is unique */
+	for (int i = 0; i < table->nprocs; i++) {
+		struct offset *a = table->offset[i];
+		for (int j = 0; j < i; j++) {
+			struct offset *b = table->offset[j];
+
+			if (strcmp(a->hostname, b->hostname) == 0) {
+				fprintf(stderr, "FATAL: ranks %d and %d run in same hostname %s\n",
+						j, i, a->hostname);
+				fail = 1;
+			}
+		}
+	}
+
+	if (fail) {
+		fprintf(stderr, "Please run %s with one rank per host\n", progname);
+		exit(EXIT_FAILURE);
+	}
+
 	fprintf(out, "%-10s %-20s %-20s %-20s %-20s\n",
 			"rank", "hostname", "offset_median", "offset_mean", "offset_std");