hw/xen/xen-hvm-common: skip ioreq creation on ioreq registration failure

On ARM it is possible to have a functioning xenpv machine with only the
PV backends and no IOREQ server. If the IOREQ server creation fails continue
to the PV backends initialization.

Also, moved the IOREQ registration and mapping subroutine to new function
xen_do_ioreq_register().

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Signed-off-by: Vikram Garhwal <vikram.garhwal@amd.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Paul Durrant <paul@xen.org>

hw/xen/xen-hvm-common.c

@@ -764,27 +764,12 @@ void xen_shutdown_fatal_error(const char *fmt, ...)
     qemu_system_shutdown_request(SHUTDOWN_CAUSE_HOST_ERROR);
 }
 
-void xen_register_ioreq(XenIOState *state, unsigned int max_cpus,
-                        MemoryListener xen_memory_listener)
+static void xen_do_ioreq_register(XenIOState *state,
+                                           unsigned int max_cpus,
+                                           MemoryListener xen_memory_listener)
 {
     int i, rc;
 
-    setup_xen_backend_ops();
-
-    state->xce_handle = qemu_xen_evtchn_open();
-    if (state->xce_handle == NULL) {
-        perror("xen: event channel open");
-        goto err;
-    }
-
-    state->xenstore = xs_daemon_open();
-    if (state->xenstore == NULL) {
-        perror("xen: xenstore open");
-        goto err;
-    }
-
-    xen_create_ioreq_server(xen_domid, &state->ioservid);
-
     state->exit.notify = xen_exit_notifier;
     qemu_add_exit_notifier(&state->exit);
 
@@ -849,12 +834,46 @@ void xen_register_ioreq(XenIOState *state, unsigned int max_cpus,
     QLIST_INIT(&state->dev_list);
     device_listener_register(&state->device_listener);
 
+    return;
+
+err:
+    error_report("xen hardware virtual machine initialisation failed");
+    exit(1);
+}
+
+void xen_register_ioreq(XenIOState *state, unsigned int max_cpus,
+                        MemoryListener xen_memory_listener)
+{
+    int rc;
+
+    setup_xen_backend_ops();
+
+    state->xce_handle = qemu_xen_evtchn_open();
+    if (state->xce_handle == NULL) {
+        perror("xen: event channel open");
+        goto err;
+    }
+
+    state->xenstore = xs_daemon_open();
+    if (state->xenstore == NULL) {
+        perror("xen: xenstore open");
+        goto err;
+    }
+
+    rc = xen_create_ioreq_server(xen_domid, &state->ioservid);
+    if (!rc) {
+        xen_do_ioreq_register(state, max_cpus, xen_memory_listener);
+    } else {
+        warn_report("xen: failed to create ioreq server");
+    }
+
     xen_bus_init();
 
     xen_be_init();
 
     return;
+
 err:
-    error_report("xen hardware virtual machine initialisation failed");
+    error_report("xen hardware virtual machine backend registration failed");
     exit(1);
 }