[Virtio-fs] [PATCH v3 1/1] vhost-user-fs: add migration type property

[Anton Kuchin]

On 22/02/2023 14:20, Vladimir Sementsov-Ogievskiy wrote:
> On 17.02.23 20:00, Anton Kuchin wrote:
>> Migration of vhost-user-fs device requires transfer of FUSE internal 
>> state
>> from backend. There is no standard way to do it now so by default 
>> migration
>> must be blocked. But if this state can be externally transferred by
>> orchestrator give it an option to explicitly allow migration.
>>
>> Signed-off-by: Anton Kuchin <antonkuchin at yandex-team.ru>
>> ---
>>   hw/core/qdev-properties-system.c    | 10 +++++++++
>>   hw/virtio/vhost-user-fs.c           | 32 ++++++++++++++++++++++++++++-
>>   include/hw/qdev-properties-system.h |  1 +
>>   include/hw/virtio/vhost-user-fs.h   |  2 ++
>>   qapi/migration.json                 | 16 +++++++++++++++
>>   5 files changed, 60 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/core/qdev-properties-system.c 
>> b/hw/core/qdev-properties-system.c
>> index d42493f630..d9b1aa2a5d 100644
>> --- a/hw/core/qdev-properties-system.c
>> +++ b/hw/core/qdev-properties-system.c
>> @@ -1143,3 +1143,13 @@ const PropertyInfo qdev_prop_uuid = {
>>       .set   = set_uuid,
>>       .set_default_value = set_default_uuid_auto,
>>   };
>> +
>> +const PropertyInfo qdev_prop_vhost_user_migration_type = {
>> +    .name = "VhostUserMigrationType",
>> +    .description = "none/external",
>> +    .enum_table = &VhostUserMigrationType_lookup,
>> +    .get = qdev_propinfo_get_enum,
>> +    .set = qdev_propinfo_set_enum,
>> +    .set_default_value = qdev_propinfo_set_default_value_enum,
>> +    .realized_set_allowed = true,
>> +};
>> diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
>> index 83fc20e49e..7deb9df5ec 100644
>> --- a/hw/virtio/vhost-user-fs.c
>> +++ b/hw/virtio/vhost-user-fs.c
>> @@ -298,9 +298,35 @@ static struct vhost_dev 
>> *vuf_get_vhost(VirtIODevice *vdev)
>>       return &fs->vhost_dev;
>>   }
>>   +static int vhost_user_fs_pre_save(void *opaque)
>> +{
>> +    VHostUserFS *fs = opaque;
>> +    g_autofree char *path = object_get_canonical_path(OBJECT(fs));
>> +
>> +    switch (fs->migration_type) {
>> +    case VHOST_USER_MIGRATION_TYPE_NONE:
>> +        error_report("Migration is blocked by device %s", path);
>> +        break;
>> +    case VHOST_USER_MIGRATION_TYPE_EXTERNAL:
>> +        return 0;
>> +    default:
>> +        error_report("Migration type '%s' is not supported by device 
>> %s",
>> + VhostUserMigrationType_str(fs->migration_type), path);
>> +        break;
>> +    }
>> +
>> +    return -1;
>> +}
>
> Should we also add this as .pre_load, to force user select correct 
> migration_type on target too?

Why do we need it? Enum forces user to select at least one of the sane 
option
and I believe this is enough. As this property affects only save and 
don't know
what we can do at load.

>
>> +
>>   static const VMStateDescription vuf_vmstate = {
>>       .name = "vhost-user-fs",
>> -    .unmigratable = 1,
>> +    .minimum_version_id = 0,
>> +    .version_id = 0,
>> +    .fields = (VMStateField[]) {
>> +        VMSTATE_VIRTIO_DEVICE,
>> +        VMSTATE_END_OF_LIST()
>> +    },
>> +   .pre_save = vhost_user_fs_pre_save,
>>   };
>>     static Property vuf_properties[] = {
>> @@ -309,6 +335,10 @@ static Property vuf_properties[] = {
>>       DEFINE_PROP_UINT16("num-request-queues", VHostUserFS,
>>                          conf.num_request_queues, 1),
>>       DEFINE_PROP_UINT16("queue-size", VHostUserFS, conf.queue_size, 
>> 128),
>> +    DEFINE_PROP_UNSIGNED("migration", VHostUserFS, migration_type,
>> +                         VHOST_USER_MIGRATION_TYPE_NONE,
>> +                         qdev_prop_vhost_user_migration_type,
>> +                         VhostUserMigrationType),
>
> 1. I see, other similar qdev_prop_* use DEFINE_PROP_SIGNED

I don't think this should be signed. Enum values are non-negative so 
compilers
(at least gcc and clang that I checked) evaluate underlying enum type to 
be unsigned int.
I don't know why other property types use signed, may be they have 
reasons or just this
is how they were initially implemented.

> 2. All of them except only qdev_prop_fdc_drive_type, define also a 
> convenient macro in include/hw/qdev-properties-system.h

This makes sense if property is used in more than one place, in this 
case I don't see any
benefit from writing more code to handle this specific case. Maybe if 
property finds its
usage in other devices this can be done.

>
> should we follow these patterns?
>
>