Re: [PATCH v5 04/10] vfio: Use new Error** argument in vfio_save_setup()

["Cédric Le Goater" <clg@redhat.com>]

On 5/13/24 15:21, Avihai Horon wrote:
> 
> On 06/05/2024 12:20, Cédric Le Goater wrote:
>> External email: Use caution opening links or attachments
> 
> Nit: change commit title prefix to vfio/migration (also in other patches that are closely related to vfio migration)
> 
> Plus, maybe change subject to "Add an Error** argument to vfio_migration_set_state() and adjust callers" as it's the main subject of the patch?
> 
>>
>> Add an Error** argument to vfio_migration_set_state() and adjust
>> callers, including vfio_save_setup(). The error will be propagated up
>> to qemu_savevm_state_setup() where the save_setup() handler is
>> executed.
>>
>> Modify vfio_vmstate_change_prepare() and vfio_vmstate_change() to
>> store a reported error under the migration stream if a migration is in
>> progress.
>>
>> Signed-off-by: Cédric Le Goater <clg@redhat.com>
>> ---
>>
>>   Changes in v5:
>>
>>   - Replaced error_setg() by error_setg_errno() in vfio_migration_set_state()
>>   - Rebased on 20c64c8a51a4 ("migration: migration_file_set_error")
>>
>>   hw/vfio/migration.c | 76 +++++++++++++++++++++++++--------------------
>>   1 file changed, 43 insertions(+), 33 deletions(-)
>>
>> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
>> index bf2fd0759ba6e4fb103cc5c1a43edb180a3d0de4..9b6375c949f7a8dca857ead2506855f63fa051e4 100644
>> --- a/hw/vfio/migration.c
>> +++ b/hw/vfio/migration.c
>> @@ -82,7 +82,8 @@ static const char *mig_state_to_str(enum vfio_device_mig_state state)
>>
>>   static int vfio_migration_set_state(VFIODevice *vbasedev,
>>                                       enum vfio_device_mig_state new_state,
>> -                                    enum vfio_device_mig_state recover_state)
>> +                                    enum vfio_device_mig_state recover_state,
>> +                                    Error **errp)
>>   {
>>       VFIOMigration *migration = vbasedev->migration;
>>       uint64_t buf[DIV_ROUND_UP(sizeof(struct vfio_device_feature) +
>> @@ -102,25 +103,26 @@ static int vfio_migration_set_state(VFIODevice *vbasedev,
>>           ret = -errno;
>>
>>           if (recover_state == VFIO_DEVICE_STATE_ERROR) {
>> -            error_report("%s: Failed setting device state to %s, err: %s. "
>> -                         "Recover state is ERROR. Resetting device",
>> -                         vbasedev->name, mig_state_to_str(new_state),
>> -                         strerror(errno));
>> +            error_setg_errno(errp, errno,
>> +                             "%s: Failed setting device state to %s. "
>> +                             "Recover state is ERROR. Resetting device",
>> +                             vbasedev->name, mig_state_to_str(new_state));
>>
>>               goto reset_device;
>>           }
>>
>> -        error_report(
>> -            "%s: Failed setting device state to %s, err: %s. Setting device in recover state %s",
>> -                     vbasedev->name, mig_state_to_str(new_state),
>> -                     strerror(errno), mig_state_to_str(recover_state));
>> +        error_setg_errno(errp, errno,
>> +                         "%s: Failed setting device state to %s. "
>> +                         "Setting device in recover state %s",
>> +                         vbasedev->name, mig_state_to_str(new_state),
>> +                         mig_state_to_str(recover_state));
>>
>>           mig_state->device_state = recover_state;
>>           if (ioctl(vbasedev->fd, VFIO_DEVICE_FEATURE, feature)) {
>>               ret = -errno;
>> -            error_report(
>> -                "%s: Failed setting device in recover state, err: %s. Resetting device",
>> -                         vbasedev->name, strerror(errno));
>> +            error_setg_errno(errp, errno,
>> +                             "%s: Failed setting device in recover state. "
>> +                             "Resetting device", vbasedev->name);
> 
> Here we set errp again when it's already set.

yes.

> Maybe in this case just:
> 
> error_report_err(*errp);
> *errp = NULL;
> error_setg_errno(errp, errno,
>                   "%s: Failed setting device in recover state. "
>                   "Resetting device", vbasedev->name);
> ?


I see two alternatives for the recover state error :

1. append to the existing one, but we lack an error_append() helper
2. report as done today.

I tend to prefer 2. and we cab come back to 1. later on.

> 
>>
>>               goto reset_device;
>>           }
>> @@ -137,7 +139,7 @@ static int vfio_migration_set_state(VFIODevice *vbasedev,
>>                * This can happen if the device is asynchronously reset and
>>                * terminates a data transfer.
>>                */
>> -            error_report("%s: data_fd out of sync", vbasedev->name);
>> +            error_setg(errp, "%s: data_fd out of sync", vbasedev->name);
>>               close(mig_state->data_fd);
>>
>>               return -EBADF;
>> @@ -168,10 +170,11 @@ reset_device:
>>    */
>>   static int
>>   vfio_migration_set_state_or_reset(VFIODevice *vbasedev,
>> -                                  enum vfio_device_mig_state new_state)
>> +                                  enum vfio_device_mig_state new_state,
>> +                                  Error **errp)
>>   {
>>       return vfio_migration_set_state(vbasedev, new_state,
>> -                                    VFIO_DEVICE_STATE_ERROR);
>> +                                    VFIO_DEVICE_STATE_ERROR, errp);
>>   }
>>
>>   static int vfio_load_buffer(QEMUFile *f, VFIODevice *vbasedev,
>> @@ -399,10 +402,8 @@ static int vfio_save_setup(QEMUFile *f, void *opaque, Error **errp)
>>           switch (migration->device_state) {
>>           case VFIO_DEVICE_STATE_RUNNING:
>>               ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_PRE_COPY,
>> -                                           VFIO_DEVICE_STATE_RUNNING);
>> +                                           VFIO_DEVICE_STATE_RUNNING, errp);
>>               if (ret) {
>> -                error_setg(errp, "%s: Failed to set new PRE_COPY state",
>> -                           vbasedev->name);
>>                   return ret;
>>               }
>>
>> @@ -435,13 +436,20 @@ static void vfio_save_cleanup(void *opaque)
>>   {
>>       VFIODevice *vbasedev = opaque;
>>       VFIOMigration *migration = vbasedev->migration;
>> +    Error *local_err = NULL;
>> +    int ret;
>>
>>       /*
>>        * Changing device state from STOP_COPY to STOP can take time. Do it here,
>>        * after migration has completed, so it won't increase downtime.
>>        */
>>       if (migration->device_state == VFIO_DEVICE_STATE_STOP_COPY) {
>> -        vfio_migration_set_state_or_reset(vbasedev, VFIO_DEVICE_STATE_STOP);
>> +        ret = vfio_migration_set_state_or_reset(vbasedev,
>> +                                                VFIO_DEVICE_STATE_STOP,
>> +                                                &local_err);
>> +        if (ret) {
>> +            error_report_err(local_err);
>> +        }
>>       }
>>
>>       g_free(migration->data_buffer);
>> @@ -549,11 +557,13 @@ static int vfio_save_complete_precopy(QEMUFile *f, void *opaque)
>>       VFIODevice *vbasedev = opaque;
>>       ssize_t data_size;
>>       int ret;
>> +    Error *local_err = NULL;
>>
>>       /* We reach here with device state STOP or STOP_COPY only */
>>       ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_STOP_COPY,
>> -                                   VFIO_DEVICE_STATE_STOP);
>> +                                   VFIO_DEVICE_STATE_STOP, &local_err);
>>       if (ret) {
>> +        error_report_err(local_err);
>>           return ret;
>>       }
>>
>> @@ -591,14 +601,9 @@ static void vfio_save_state(QEMUFile *f, void *opaque)
>>   static int vfio_load_setup(QEMUFile *f, void *opaque, Error **errp)
>>   {
>>       VFIODevice *vbasedev = opaque;
>> -    int ret;
>>
>> -    ret = vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
>> -                                   vbasedev->migration->device_state);
>> -    if (ret) {
>> -        error_setg(errp, "%s: Failed to set RESUMING state", vbasedev->name);
>> -    }
>> -    return ret;
>> +    return vfio_migration_set_state(vbasedev, VFIO_DEVICE_STATE_RESUMING,
>> +                                    vbasedev->migration->device_state, errp);
>>   }
>>
>>   static int vfio_load_cleanup(void *opaque)
>> @@ -714,19 +719,20 @@ static void vfio_vmstate_change_prepare(void *opaque, bool running,
>>       VFIODevice *vbasedev = opaque;
>>       VFIOMigration *migration = vbasedev->migration;
>>       enum vfio_device_mig_state new_state;
>> +    Error *local_err = NULL;
>>       int ret;
>>
>>       new_state = migration->device_state == VFIO_DEVICE_STATE_PRE_COPY ?
>>                       VFIO_DEVICE_STATE_PRE_COPY_P2P :
>>                       VFIO_DEVICE_STATE_RUNNING_P2P;
>>
>> -    ret = vfio_migration_set_state_or_reset(vbasedev, new_state);
>> +    ret = vfio_migration_set_state_or_reset(vbasedev, new_state, &local_err);
>>       if (ret) {
>>           /*
>>            * Migration should be aborted in this case, but vm_state_notify()
>>            * currently does not support reporting failures.
>>            */
>> -        migration_file_set_error(ret, NULL);
>> +        migration_file_set_error(ret, local_err);
>>       }
>>
>>       trace_vfio_vmstate_change_prepare(vbasedev->name, running,
>> @@ -738,6 +744,7 @@ static void vfio_vmstate_change(void *opaque, bool running, RunState state)
>>   {
>>       VFIODevice *vbasedev = opaque;
>>       enum vfio_device_mig_state new_state;
>> +    Error *local_err = NULL;
>>       int ret;
>>
>>       if (running) {
>> @@ -750,13 +757,13 @@ static void vfio_vmstate_change(void *opaque, bool running, RunState state)
>>                   VFIO_DEVICE_STATE_STOP;
>>       }
>>
>> -    ret = vfio_migration_set_state_or_reset(vbasedev, new_state);
>> +    ret = vfio_migration_set_state_or_reset(vbasedev, new_state, &local_err);
>>       if (ret) {
>>           /*
>>            * Migration should be aborted in this case, but vm_state_notify()
>>            * currently does not support reporting failures.
>>            */
>> -        migration_file_set_error(ret, NULL);
>> +        migration_file_set_error(ret, local_err);
>>       }
>>
>>       trace_vfio_vmstate_change(vbasedev->name, running, RunState_str(state),
>> @@ -769,13 +776,16 @@ static int vfio_migration_state_notifier(NotifierWithReturn *notifier,
>>       VFIOMigration *migration = container_of(notifier, VFIOMigration,
>>                                               migration_state);
>>       VFIODevice *vbasedev = migration->vbasedev;
>> +    int ret = 0;
>>
>>       trace_vfio_migration_state_notifier(vbasedev->name, e->type);
>>
>>       if (e->type == MIG_EVENT_PRECOPY_FAILED) {
>> -        vfio_migration_set_state_or_reset(vbasedev, VFIO_DEVICE_STATE_RUNNING);
>> +        ret = vfio_migration_set_state_or_reset(vbasedev,
>> +                                                VFIO_DEVICE_STATE_RUNNING,
>> +                                                errp);
>>       }
>> -    return 0;
>> +    return ret;
> 
> In MigrationNotifyFunc declaration it's stated that:
> 
> /*
>   * A MigrationNotifyFunc may return an error code and an Error object,
>   * but only when @e->type is MIG_EVENT_PRECOPY_SETUP.  The code is an int
>   * to allow for different failure modes and recovery actions.
>   */
> 
> And indeed migration_call_notifiers() will assert if this notifier fails on MIG_EVENT_PRECOPY_FAILED.

My series has been out of tree for too long :/

> So I guess we should simply report the error locally and return 0.

yes. That said, I don't see why migrate_fd_cleanup() or postcopy_start()
could not use a local_err and report the error themselves. For later.
I will add a comment though.

Thanks,

C.


> 
> Thanks.
> 
>>   }
>>
>>   static void vfio_migration_free(VFIODevice *vbasedev)
>> -- 
>> 2.45.0
>>
>