Re: [PATCH] migration: Provide a test for migratability

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 21 Jan 2021 18:51:13 +0000
"Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:

> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Provide a simple way to see if there's currently a migration blocker in
> operation:
> 
> $ ./x86_64-softmmu/qemu-system-x86_64 -nographic -M pc,usb=on -chardev null,id=n -device usb-serial,chardev=n
> 
> (qemu) info migratable
> Error: State blocked by non-migratable device '0000:00:01.2/1/usb-serial'

FWIW, a vfio device gets:

(qemu) info migratable
Error: VFIO device doesn't support migration

I think your example is getting the device string because you're
testing something with unmigratable = 1 in the vmsd and the iterator
prints a generic string plus the device, we'd need to make our error
message include the device info.  But even without that it seems more
useful than we have currently.  Thanks

Tested-by: Alex Williamson <alex.williamson@redhat.com>

> $ ./x86_64-softmmu/qemu-system-x86_64 -nographic
> 
> (qemu) info migratable
> Migratable
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  hmp-commands-info.hx  | 14 ++++++++++++++
>  include/monitor/hmp.h |  1 +
>  migration/migration.c |  5 +++++
>  monitor/hmp-cmds.c    | 13 +++++++++++++
>  qapi/migration.json   | 14 ++++++++++++++
>  5 files changed, 47 insertions(+)
> 
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 117ba25f91..c2d7ac2f11 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -541,6 +541,20 @@ SRST
>      Show migration status.
>  ERST
>  
> +    {
> +        .name       = "migratable",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "tests if VM is migratable",
> +        .cmd        = hmp_info_migratable,
> +    },
> +
> +SRST
> +  ''info migratable''
> +    Tests whether the VM is currently migratable.
> +ERST
> +
> +
>      {
>          .name       = "migrate_capabilities",
>          .args_type  = "",
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index ed2913fd18..0dd7941daf 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -25,6 +25,7 @@ void hmp_info_status(Monitor *mon, const QDict *qdict);
>  void hmp_info_uuid(Monitor *mon, const QDict *qdict);
>  void hmp_info_chardev(Monitor *mon, const QDict *qdict);
>  void hmp_info_mice(Monitor *mon, const QDict *qdict);
> +void hmp_info_migratable(Monitor *mon, const QDict *qdict);
>  void hmp_info_migrate(Monitor *mon, const QDict *qdict);
>  void hmp_info_migrate_capabilities(Monitor *mon, const QDict *qdict);
>  void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict);
> diff --git a/migration/migration.c b/migration/migration.c
> index 5e330cc6eb..8745a5b9f9 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -2234,6 +2234,11 @@ int64_t qmp_query_migrate_cache_size(Error **errp)
>      return migrate_xbzrle_cache_size();
>  }
>  
> +void qmp_query_migratable(Error **errp)
> +{
> +    migration_is_blocked(errp);
> +}
> +
>  void qmp_migrate_set_speed(int64_t value, Error **errp)
>  {
>      MigrateSetParameters p = {
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index ef569035f8..a7f48b3512 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -216,6 +216,19 @@ static char *SocketAddress_to_str(SocketAddress *addr)
>      }
>  }
>  
> +void hmp_info_migratable(Monitor *mon, const QDict *qdict)
> +{
> +    Error *err = NULL;
> +    /* It's migratable if this succeeds */
> +    qmp_query_migratable(&err);
> +    if (err) {
> +        hmp_handle_error(mon, err);
> +        return;
> +    }
> +
> +    monitor_printf(mon, "Migratable\n");
> +}
> +
>  void hmp_info_migrate(Monitor *mon, const QDict *qdict)
>  {
>      MigrationInfo *info;
> diff --git a/qapi/migration.json b/qapi/migration.json
> index d1d9632c2a..07aee9907c 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -366,6 +366,20 @@
>  ##
>  { 'command': 'query-migrate', 'returns': 'MigrationInfo' }
>  
> +##
> +# @query-migratable:
> +# Tests whether it will be possible to migrate the VM in the current state.
> +#
> +# Returns: nothing on success (i.e. if the VM is migratable)
> +#
> +# Since: 6.0
> +# Example:
> +#
> +# -> { "execute": "query-migratable" }
> +# <- { "return": {} }
> +##
> +{ 'command': 'query-migratable' }
> +
>  ##
>  # @MigrationCapability:
>  #