migration: Unify failure check for migrate_add_blocker()

Most callers check the return value.  Some check whether it set an
error.  Functionally equivalent, but the former tends to be easier on
the eyes, so do that everywhere.

Prior art: commit c6ecec4 "qemu-option: Check return value instead
of @err where convenient".

Signed-off-by: Markus Armbruster <[email protected]>
Message-Id: <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>

Author: Markus Armbruster

backends/tpm/tpm_emulator.c

@@ -492,8 +492,7 @@ static int tpm_emulator_block_migration(TPMEmulator *tpm_emu)
         error_setg(&tpm_emu->migration_blocker,
                    "Migration disabled: TPM emulator does not support "
                    "migration");
-        migrate_add_blocker(tpm_emu->migration_blocker, &err);
-        if (err) {
+        if (migrate_add_blocker(tpm_emu->migration_blocker, &err) < 0) {
             error_report_err(err);
             error_free(tpm_emu->migration_blocker);
             tpm_emu->migration_blocker = NULL;

hw/virtio/vhost.c

@@ -1372,7 +1372,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
 
     if (hdev->migration_blocker != NULL) {
         r = migrate_add_blocker(hdev->migration_blocker, errp);
-        if (*errp) {
+        if (r < 0) {
             error_free(hdev->migration_blocker);
             goto fail_busyloop;
         }

target/i386/kvm/kvm.c

@@ -1435,7 +1435,7 @@ static int hyperv_init_vcpu(X86CPU *cpu)
                    "'hv-passthrough' CPU flag prevents migration, use explicit"
                    " set of hv-* flags instead");
         ret = migrate_add_blocker(hv_passthrough_mig_blocker, &local_err);
-        if (local_err) {
+        if (ret < 0) {
             error_report_err(local_err);
             return ret;
         }
@@ -1449,7 +1449,7 @@ static int hyperv_init_vcpu(X86CPU *cpu)
                    " make sure SMT is disabled and/or that vCPUs are properly"
                    " pinned)");
         ret = migrate_add_blocker(hv_no_nonarch_cs_mig_blocker, &local_err);
-        if (local_err) {
+        if (ret < 0) {
             error_report_err(local_err);
             return ret;
         }
@@ -1888,7 +1888,7 @@ int kvm_arch_init_vcpu(CPUState *cs)
                        "State blocked by non-migratable CPU device"
                        " (invtsc flag)");
             r = migrate_add_blocker(invtsc_mig_blocker, &local_err);
-            if (local_err) {
+            if (r < 0) {
                 error_report_err(local_err);
                 return r;
             }

target/i386/nvmm/nvmm-all.c

@@ -926,8 +926,7 @@ nvmm_init_vcpu(CPUState *cpu)
         error_setg(&nvmm_migration_blocker,
             "NVMM: Migration not supported");
 
-        (void)migrate_add_blocker(nvmm_migration_blocker, &local_error);
-        if (local_error) {
+        if (migrate_add_blocker(nvmm_migration_blocker, &local_error) < 0) {
             error_report_err(local_error);
             error_free(nvmm_migration_blocker);
             return -EINVAL;

target/i386/whpx/whpx-all.c

@@ -1346,8 +1346,7 @@ int whpx_init_vcpu(CPUState *cpu)
                "State blocked due to non-migratable CPUID feature support,"
                "dirty memory tracking support, and XSAVE/XRSTOR support");
 
-        (void)migrate_add_blocker(whpx_migration_blocker, &local_error);
-        if (local_error) {
+        if (migrate_add_blocker(whpx_migration_blocker, &local_error) < 0) {
             error_report_err(local_error);
             error_free(whpx_migration_blocker);
             ret = -EINVAL;