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>

4 files changed, 8 insertions, 11 deletions

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 {