[Qemu-devel] [PATCH v2] numa: improve cpu hotplug error message with a wrong node-id

[Laurent Vivier <lvivier@redhat.com>]

On pseries, core-ids are strongly binded to a node-id by the command
line option. If an user tries to add a CPU to the wrong node, he has
an error but it is not really helpful:

  qemu-system-ppc64 ... -smp 1,maxcpus=64,cores=1,threads=1,sockets=1 \
                        -numa node,nodeid=0 -numa node,nodeid=1 ...

  (qemu) device_add power9_v2.0-spapr-cpu-core,core-id=30,node-id=1
  Error: node-id=1 must match numa node specified with -numa option

This patch improves this error message by giving to the user the good
topology information (node-id, socket-id and thread-id if they are
available) to use with the core-id he's providing:

  Error: core-id 30 can only be plugged into node-id 0

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---

Notes:
    v2: display full topology in the error message

 numa.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/numa.c b/numa.c
index 3875e1efda3a..7413f821e2bb 100644
--- a/numa.c
+++ b/numa.c
@@ -458,6 +458,27 @@ void qmp_set_numa_node(NumaOptions *cmd, Error **errp)
     set_numa_options(MACHINE(qdev_get_machine()), cmd, errp);
 }
 
+static char *cpu_topology_to_string(const CPUArchId *cpu)
+{
+    GString *s = g_string_new(NULL);
+    if (cpu->props.has_socket_id) {
+        g_string_append_printf(s, "socket-id %"PRId64, cpu->props.socket_id);
+    }
+    if (cpu->props.has_node_id) {
+        if (s->len) {
+            g_string_append_printf(s, ", ");
+        }
+        g_string_append_printf(s, "node-id %"PRId64, cpu->props.node_id);
+    }
+    if (cpu->props.has_thread_id) {
+        if (s->len) {
+            g_string_append_printf(s, ", ");
+        }
+        g_string_append_printf(s, "thread-id %"PRId64, cpu->props.thread_id);
+    }
+    return g_string_free(s, false);
+}
+
 void numa_cpu_pre_plug(const CPUArchId *slot, DeviceState *dev, Error **errp)
 {
     int node_id = object_property_get_int(OBJECT(dev), "node-id", &error_abort);
@@ -470,8 +491,11 @@ void numa_cpu_pre_plug(const CPUArchId *slot, DeviceState *dev, Error **errp)
                                     "node-id", errp);
         }
     } else if (node_id != slot->props.node_id) {
-        error_setg(errp, "node-id=%d must match numa node specified "
-                   "with -numa option", node_id);
+        char *topology = cpu_topology_to_string(slot);
+        error_setg(errp,
+                   "core-id %"PRId64" can only be plugged into %s",
+                   slot->props.core_id, topology);
+        g_free(topology);
     }
 }
 
-- 
2.20.1