migration: simplify blockers

Modify migrate_add_blocker and migrate_del_blocker to take an Error **
reason.  This allows migration to own the Error object, so that if
an error occurs in migrate_add_blocker, migration code can free the Error
and clear the client handle, simplifying client code.  It also simplifies
the migrate_del_blocker call site.

In addition, this is a pre-requisite for a proposed future patch that would
add a mode argument to migration requests to support live update, and
maintain a list of blockers for each mode.  A blocker may apply to a single
mode or to multiple modes, and passing Error** will allow one Error object
to be registered for multiple modes.

No functional change.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Tested-by: Michael Galaxy <mgalaxy@akamai.com>
Reviewed-by: Michael Galaxy <mgalaxy@akamai.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Message-ID: <1697634216-84215-1-git-send-email-steven.sistare@oracle.com>

16 files changed, 31 insertions, 81 deletions

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 323f042e65..af636cfb2d 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -406,11 +406,7 @@ static int coroutine_fn put_fid(V9fsPDU *pdu, V9fsFidState *fidp)
              * delete the migration blocker. Ideally, this
              * should be hooked to transport close notification
              */
-            if (pdu->s->migration_blocker) {
-                migrate_del_blocker(pdu->s->migration_blocker);
-                error_free(pdu->s->migration_blocker);
-                pdu->s->migration_blocker = NULL;
-            }
+            migrate_del_blocker(&pdu->s->migration_blocker);
         }
         return free_fid(pdu, fidp);
     }
@@ -1505,10 +1501,8 @@ static void coroutine_fn v9fs_attach(void *opaque)
         error_setg(&s->migration_blocker,
                    "Migration is disabled when VirtFS export path '%s' is mounted in the guest using mount_tag '%s'",
                    s->ctx.fs_root ? s->ctx.fs_root : "NULL", s->tag);
-        err = migrate_add_blocker(s->migration_blocker, NULL);
+        err = migrate_add_blocker(&s->migration_blocker, NULL);
         if (err < 0) {
-            error_free(s->migration_blocker);
-            s->migration_blocker = NULL;
             clunk_fid(s, fid);
             goto out;
         }
diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index 50c5373b65..37af256219 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -184,8 +184,7 @@ virtio_gpu_base_device_realize(DeviceState *qdev,
 
     if (virtio_gpu_virgl_enabled(g->conf)) {
         error_setg(&g->migration_blocker, "virgl is not yet migratable");
-        if (migrate_add_blocker(g->migration_blocker, errp) < 0) {
-            error_free(g->migration_blocker);
+        if (migrate_add_blocker(&g->migration_blocker, errp) < 0) {
             return false;
         }
     }
@@ -253,10 +252,7 @@ virtio_gpu_base_device_unrealize(DeviceState *qdev)
 {
     VirtIOGPUBase *g = VIRTIO_GPU_BASE(qdev);
 
-    if (g->migration_blocker) {
-        migrate_del_blocker(g->migration_blocker);
-        error_free(g->migration_blocker);
-    }
+    migrate_del_blocker(&g->migration_blocker);
 }
 
 static void
diff --git a/hw/intc/arm_gic_kvm.c b/hw/intc/arm_gic_kvm.c
index 1d588946bc..e0d9e512a3 100644
--- a/hw/intc/arm_gic_kvm.c
+++ b/hw/intc/arm_gic_kvm.c
@@ -516,8 +516,7 @@ static void kvm_arm_gic_realize(DeviceState *dev, Error **errp)
     if (!kvm_arm_gic_can_save_restore(s)) {
         error_setg(&s->migration_blocker, "This operating system kernel does "
                                           "not support vGICv2 migration");
-        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
-            error_free(s->migration_blocker);
+        if (migrate_add_blocker(&s->migration_blocker, errp) < 0) {
             return;
         }
     }
diff --git a/hw/intc/arm_gicv3_its_kvm.c b/hw/intc/arm_gicv3_its_kvm.c
index 7eda9fb86e..61c1cc7bdb 100644
--- a/hw/intc/arm_gicv3_its_kvm.c
+++ b/hw/intc/arm_gicv3_its_kvm.c
@@ -114,8 +114,7 @@ static void kvm_arm_its_realize(DeviceState *dev, Error **errp)
         GITS_CTLR)) {
         error_setg(&s->migration_blocker, "This operating system kernel "
                    "does not support vITS migration");
-        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
-            error_free(s->migration_blocker);
+        if (migrate_add_blocker(&s->migration_blocker, errp) < 0) {
             return;
         }
     } else {
diff --git a/hw/intc/arm_gicv3_kvm.c b/hw/intc/arm_gicv3_kvm.c
index 72ad916d3d..77eb37e131 100644
--- a/hw/intc/arm_gicv3_kvm.c
+++ b/hw/intc/arm_gicv3_kvm.c
@@ -878,8 +878,7 @@ static void kvm_arm_gicv3_realize(DeviceState *dev, Error **errp)
                                GICD_CTLR)) {
         error_setg(&s->migration_blocker, "This operating system kernel does "
                                           "not support vGICv3 migration");
-        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
-            error_free(s->migration_blocker);
+        if (migrate_add_blocker(&s->migration_blocker, errp) < 0) {
             return;
         }
     }
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index d66d912172..0447888029 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -903,8 +903,7 @@ static void ivshmem_common_realize(PCIDevice *dev, Error **errp)
     if (!ivshmem_is_master(s)) {
         error_setg(&s->migration_blocker,
                    "Migration is disabled when using feature 'peer mode' in device 'ivshmem'");
-        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
-            error_free(s->migration_blocker);
+        if (migrate_add_blocker(&s->migration_blocker, errp) < 0) {
             return;
         }
     }
@@ -922,10 +921,7 @@ static void ivshmem_exit(PCIDevice *dev)
     IVShmemState *s = IVSHMEM_COMMON(dev);
     int i;
 
-    if (s->migration_blocker) {
-        migrate_del_blocker(s->migration_blocker);
-        error_free(s->migration_blocker);
-    }
+    migrate_del_blocker(&s->migration_blocker);
 
     if (memory_region_is_mapped(s->ivshmem_bar2)) {
         if (!s->hostmem) {
diff --git a/hw/ppc/pef.c b/hw/ppc/pef.c
index cc44d5e339..d28ed3ba73 100644
--- a/hw/ppc/pef.c
+++ b/hw/ppc/pef.c
@@ -63,7 +63,7 @@ static int kvmppc_svm_init(ConfidentialGuestSupport *cgs, Error **errp)
     /* add migration blocker */
     error_setg(&pef_mig_blocker, "PEF: Migration is not implemented");
     /* NB: This can fail if --only-migratable is used */
-    migrate_add_blocker(pef_mig_blocker, &error_fatal);
+    migrate_add_blocker(&pef_mig_blocker, &error_fatal);
 
     cgs->ready = true;
 
diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index cb840676d3..b25093be28 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1761,7 +1761,7 @@ static void spapr_machine_reset(MachineState *machine, ShutdownCause reason)
     /* Signal all vCPUs waiting on this condition */
     qemu_cond_broadcast(&spapr->fwnmi_machine_check_interlock_cond);
 
-    migrate_del_blocker(spapr->fwnmi_migration_blocker);
+    migrate_del_blocker(&spapr->fwnmi_migration_blocker);
 }
 
 static void spapr_create_nvram(SpaprMachineState *spapr)
@@ -2937,13 +2937,6 @@ static void spapr_machine_init(MachineState *machine)
         spapr_create_lmb_dr_connectors(spapr);
     }
 
-    if (spapr_get_cap(spapr, SPAPR_CAP_FWNMI) == SPAPR_CAP_ON) {
-        /* Create the error string for live migration blocker */
-        error_setg(&spapr->fwnmi_migration_blocker,
-            "A machine check is being handled during migration. The handler"
-            "may run and log hardware error on the destination");
-    }
-
     if (mc->nvdimm_supported) {
         spapr_create_nvdimm_dr_connectors(spapr);
     }
diff --git a/hw/ppc/spapr_events.c b/hw/ppc/spapr_events.c
index 4508e40814..deb4641505 100644
--- a/hw/ppc/spapr_events.c
+++ b/hw/ppc/spapr_events.c
@@ -920,7 +920,11 @@ void spapr_mce_req_event(PowerPCCPU *cpu, bool recovered)
      * fails when running with -only-migrate.  A proper interface to
      * delay migration completion for a bit could avoid that.
      */
-    ret = migrate_add_blocker(spapr->fwnmi_migration_blocker, NULL);
+    error_setg(&spapr->fwnmi_migration_blocker,
+        "A machine check is being handled during migration. The handler"
+        "may run and log hardware error on the destination");
+
+    ret = migrate_add_blocker(&spapr->fwnmi_migration_blocker, NULL);
     if (ret == -EBUSY) {
         warn_report("Received a fwnmi while migration was in progress");
     }
diff --git a/hw/ppc/spapr_rtas.c b/hw/ppc/spapr_rtas.c
index 7df21581c2..26c384b261 100644
--- a/hw/ppc/spapr_rtas.c
+++ b/hw/ppc/spapr_rtas.c
@@ -496,7 +496,7 @@ static void rtas_ibm_nmi_interlock(PowerPCCPU *cpu,
     spapr->fwnmi_machine_check_interlock = -1;
     qemu_cond_signal(&spapr->fwnmi_machine_check_interlock_cond);
     rtas_st(rets, 0, RTAS_OUT_SUCCESS);
-    migrate_del_blocker(spapr->fwnmi_migration_blocker);
+    migrate_del_blocker(&spapr->fwnmi_migration_blocker);
 }
 
 static struct rtas_call {
diff --git a/hw/remote/proxy.c b/hw/remote/proxy.c
index 2052d721e5..fbc85a8d36 100644
--- a/hw/remote/proxy.c
+++ b/hw/remote/proxy.c
@@ -107,8 +107,7 @@ static void pci_proxy_dev_realize(PCIDevice *device, Error **errp)
 
     error_setg(&dev->migration_blocker, "%s does not support migration",
                TYPE_PCI_PROXY_DEV);
-    if (migrate_add_blocker(dev->migration_blocker, errp) < 0) {
-        error_free(dev->migration_blocker);
+    if (migrate_add_blocker(&dev->migration_blocker, errp) < 0) {
         object_unref(dev->ioc);
         return;
     }
@@ -134,9 +133,7 @@ static void pci_proxy_dev_exit(PCIDevice *pdev)
         qio_channel_close(dev->ioc, NULL);
     }
 
-    migrate_del_blocker(dev->migration_blocker);
-
-    error_free(dev->migration_blocker);
+    migrate_del_blocker(&dev->migration_blocker);
 
     proxy_memory_listener_deconfigure(&dev->proxy_listener);
 
diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index 2d75f2131f..07a5157c0f 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -332,8 +332,7 @@ static void s390_machine_unprotect(S390CcwMachineState *ms)
         s390_pv_vm_disable();
     }
     ms->pv = false;
-    migrate_del_blocker(pv_mig_blocker);
-    error_free_or_abort(&pv_mig_blocker);
+    migrate_del_blocker(&pv_mig_blocker);
     ram_block_discard_disable(false);
 }
 
@@ -356,11 +355,10 @@ static int s390_machine_protect(S390CcwMachineState *ms)
 
     error_setg(&pv_mig_blocker,
                "protected VMs are currently not migratable.");
-    rc = migrate_add_blocker(pv_mig_blocker, &local_err);
+    rc = migrate_add_blocker(&pv_mig_blocker, &local_err);
     if (rc) {
         ram_block_discard_disable(false);
         error_report_err(local_err);
-        error_free_or_abort(&pv_mig_blocker);
         return rc;
     }
 
@@ -368,8 +366,7 @@ static int s390_machine_protect(S390CcwMachineState *ms)
     rc = s390_pv_vm_enable();
     if (rc) {
         ram_block_discard_disable(false);
-        migrate_del_blocker(pv_mig_blocker);
-        error_free_or_abort(&pv_mig_blocker);
+        migrate_del_blocker(&pv_mig_blocker);
         return rc;
     }
 
diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
index 443f67daa4..14e23cc5b4 100644
--- a/hw/scsi/vhost-scsi.c
+++ b/hw/scsi/vhost-scsi.c
@@ -208,7 +208,7 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
                 "When external environment supports it (Orchestrator migrates "
                 "target SCSI device state or use shared storage over network), "
                 "set 'migratable' property to true to enable migration.");
-        if (migrate_add_blocker(vsc->migration_blocker, errp) < 0) {
+        if (migrate_add_blocker(&vsc->migration_blocker, errp) < 0) {
             goto free_virtio;
         }
     }
@@ -241,10 +241,9 @@ static void vhost_scsi_realize(DeviceState *dev, Error **errp)
  free_vqs:
     g_free(vqs);
     if (!vsc->migratable) {
-        migrate_del_blocker(vsc->migration_blocker);
+        migrate_del_blocker(&vsc->migration_blocker);
     }
  free_virtio:
-    error_free(vsc->migration_blocker);
     virtio_scsi_common_unrealize(dev);
  close_fd:
     if (vhostfd >= 0) {
@@ -260,8 +259,7 @@ static void vhost_scsi_unrealize(DeviceState *dev)
     struct vhost_virtqueue *vqs = vsc->dev.vqs;
 
     if (!vsc->migratable) {
-        migrate_del_blocker(vsc->migration_blocker);
-        error_free(vsc->migration_blocker);
+        migrate_del_blocker(&vsc->migration_blocker);
     }
 
     /* This will stop vhost backend. */
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 5ff5acf1d8..d806057b40 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -129,11 +129,7 @@ int vfio_block_multiple_devices_migration(VFIODevice *vbasedev, Error **errp)
     error_setg(&multiple_devices_migration_blocker,
                "Multiple VFIO devices migration is supported only if all of "
                "them support P2P migration");
-    ret = migrate_add_blocker(multiple_devices_migration_blocker, errp);
-    if (ret < 0) {
-        error_free(multiple_devices_migration_blocker);
-        multiple_devices_migration_blocker = NULL;
-    }
+    ret = migrate_add_blocker(&multiple_devices_migration_blocker, errp);
 
     return ret;
 }
@@ -145,9 +141,7 @@ void vfio_unblock_multiple_devices_migration(void)
         return;
     }
 
-    migrate_del_blocker(multiple_devices_migration_blocker);
-    error_free(multiple_devices_migration_blocker);
-    multiple_devices_migration_blocker = NULL;
+    migrate_del_blocker(&multiple_devices_migration_blocker);
 }
 
 bool vfio_viommu_preset(VFIODevice *vbasedev)
diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index da43dcd2fe..0aaad65c06 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -891,8 +891,6 @@ static void vfio_migration_deinit(VFIODevice *vbasedev)
 
 static int vfio_block_migration(VFIODevice *vbasedev, Error *err, Error **errp)
 {
-    int ret;
-
     if (vbasedev->enable_migration == ON_OFF_AUTO_ON) {
         error_propagate(errp, err);
         return -EINVAL;
@@ -901,13 +899,7 @@ static int vfio_block_migration(VFIODevice *vbasedev, Error *err, Error **errp)
     vbasedev->migration_blocker = error_copy(err);
     error_free(err);
 
-    ret = migrate_add_blocker(vbasedev->migration_blocker, errp);
-    if (ret < 0) {
-        error_free(vbasedev->migration_blocker);
-        vbasedev->migration_blocker = NULL;
-    }
-
-    return ret;
+    return migrate_add_blocker(&vbasedev->migration_blocker, errp);
 }
 
 /* ---------------------------------------------------------------------- */
@@ -994,9 +986,5 @@ void vfio_migration_exit(VFIODevice *vbasedev)
         vfio_migration_deinit(vbasedev);
     }
 
-    if (vbasedev->migration_blocker) {
-        migrate_del_blocker(vbasedev->migration_blocker);
-        error_free(vbasedev->migration_blocker);
-        vbasedev->migration_blocker = NULL;
-    }
+    migrate_del_blocker(&vbasedev->migration_blocker);
 }
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 9f37206ba0..d737671028 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -1527,9 +1527,8 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
     }
 
     if (hdev->migration_blocker != NULL) {
-        r = migrate_add_blocker(hdev->migration_blocker, errp);
+        r = migrate_add_blocker(&hdev->migration_blocker, errp);
         if (r < 0) {
-            error_free(hdev->migration_blocker);
             goto fail_busyloop;
         }
     }
@@ -1597,10 +1596,7 @@ void vhost_dev_cleanup(struct vhost_dev *hdev)
         memory_listener_unregister(&hdev->memory_listener);
         QLIST_REMOVE(hdev, entry);
     }
-    if (hdev->migration_blocker) {
-        migrate_del_blocker(hdev->migration_blocker);
-        error_free(hdev->migration_blocker);
-    }
+    migrate_del_blocker(&hdev->migration_blocker);
     g_free(hdev->mem);
     g_free(hdev->mem_sections);
     if (hdev->vhost_ops) {