s390/stattrib: Add Error** argument to set_migrationmode() handler

This will prepare ground for future changes adding an Error** argument
to the save_setup() handler. We need to make sure that on failure,
set_migrationmode() always sets a new error. See the Rules section in
qapi/error.h.

Cc: Halil Pasic <pasic@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Thomas Huth <thuth@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/r/20240320064911.545001-2-clg@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>

hw/s390x/s390-stattrib-kvm.c

@@ -17,6 +17,7 @@
 #include "sysemu/kvm.h"
 #include "exec/ram_addr.h"
 #include "kvm/kvm_s390x.h"
+#include "qapi/error.h"
 
 Object *kvm_s390_stattrib_create(void)
 {
@@ -137,14 +138,21 @@ static void kvm_s390_stattrib_synchronize(S390StAttribState *sa)
     }
 }
 
-static int kvm_s390_stattrib_set_migrationmode(S390StAttribState *sa, bool val)
+static int kvm_s390_stattrib_set_migrationmode(S390StAttribState *sa, bool val,
+                                               Error **errp)
 {
     struct kvm_device_attr attr = {
         .group = KVM_S390_VM_MIGRATION,
         .attr = val,
         .addr = 0,
     };
-    return kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
+    int r;
+
+    r = kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attr);
+    if (r) {
+        error_setg_errno(errp, -r, "setting KVM_S390_VM_MIGRATION failed");
+    }
+    return r;
 }
 
 static long long kvm_s390_stattrib_get_dirtycount(S390StAttribState *sa)

hw/s390x/s390-stattrib.c

@@ -60,11 +60,13 @@ void hmp_migrationmode(Monitor *mon, const QDict *qdict)
     S390StAttribState *sas = s390_get_stattrib_device();
     S390StAttribClass *sac = S390_STATTRIB_GET_CLASS(sas);
     uint64_t what = qdict_get_int(qdict, "mode");
+    Error *local_err = NULL;
     int r;
 
-    r = sac->set_migrationmode(sas, what);
+    r = sac->set_migrationmode(sas, what, &local_err);
     if (r < 0) {
-        monitor_printf(mon, "Error: %s", strerror(-r));
+        monitor_printf(mon, "Error: %s", error_get_pretty(local_err));
+        error_free(local_err);
     }
 }
 
@@ -170,13 +172,15 @@ static int cmma_save_setup(QEMUFile *f, void *opaque)
 {
     S390StAttribState *sas = S390_STATTRIB(opaque);
     S390StAttribClass *sac = S390_STATTRIB_GET_CLASS(sas);
+    Error *local_err = NULL;
     int res;
     /*
      * Signal that we want to start a migration, thus needing PGSTE dirty
      * tracking.
      */
-    res = sac->set_migrationmode(sas, 1);
+    res = sac->set_migrationmode(sas, true, &local_err);
     if (res) {
+        error_report_err(local_err);
         return res;
     }
     qemu_put_be64(f, STATTR_FLAG_EOS);
@@ -260,7 +264,7 @@ static void cmma_save_cleanup(void *opaque)
 {
     S390StAttribState *sas = S390_STATTRIB(opaque);
     S390StAttribClass *sac = S390_STATTRIB_GET_CLASS(sas);
-    sac->set_migrationmode(sas, 0);
+    sac->set_migrationmode(sas, false, NULL);
 }
 
 static bool cmma_active(void *opaque)
@@ -293,7 +297,8 @@ static long long qemu_s390_get_dirtycount_stub(S390StAttribState *sa)
 {
     return 0;
 }
-static int qemu_s390_set_migrationmode_stub(S390StAttribState *sa, bool value)
+static int qemu_s390_set_migrationmode_stub(S390StAttribState *sa, bool value,
+                                            Error **errp)
 {
     return 0;
 }

include/hw/s390x/storage-attributes.h

@@ -39,7 +39,7 @@ struct S390StAttribClass {
     int (*set_stattr)(S390StAttribState *sa, uint64_t start_gfn,
                       uint32_t count, uint8_t *values);
     void (*synchronize)(S390StAttribState *sa);
-    int (*set_migrationmode)(S390StAttribState *sa, bool value);
+    int (*set_migrationmode)(S390StAttribState *sa, bool value, Error **errp);
     int (*get_active)(S390StAttribState *sa);
     long long (*get_dirtycount)(S390StAttribState *sa);
 };