On Wed, Feb 25, 2015 at 04:51:46PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> 
> Once postcopy is enabled (with migrate_set_capability), the migration
> will still start on precopy mode.  To cause a transition into postcopy
> the:
> 
>   migrate_start_postcopy
> 
> command must be issued.  Postcopy will start sometime after this
> (when it's next checked in the migration loop).
> 
> Issuing the command before migration has started will error,
> and issuing after it has finished is ignored.
> 
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  hmp-commands.hx               | 15 +++++++++++++++
>  hmp.c                         |  7 +++++++
>  hmp.h                         |  1 +
>  include/migration/migration.h |  3 +++
>  migration/migration.c         | 22 ++++++++++++++++++++++
>  qapi-schema.json              |  8 ++++++++
>  qmp-commands.hx               | 19 +++++++++++++++++++
>  7 files changed, 75 insertions(+)
> 
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index e37bc8b..03b8b78 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -985,6 +985,21 @@ Enable/Disable the usage of a capability @var{capability} for migration.
>  ETEXI
>  
>      {
> +        .name       = "migrate_start_postcopy",
> +        .args_type  = "",
> +        .params     = "",
> +        .help       = "Switch migration to postcopy mode",
> +        .mhandler.cmd = hmp_migrate_start_postcopy,
> +    },
> +
> +STEXI
> +@item migrate_start_postcopy
> +@findex migrate_start_postcopy
> +Switch in-progress migration to postcopy mode. Ignored after the end of
> +migration (or once already in postcopy).
> +ETEXI
> +
> +    {
>          .name       = "client_migrate_info",
>          .args_type  = "protocol:s,hostname:s,port:i?,tls-port:i?,cert-subject:s?",
>          .params     = "protocol hostname port tls-port cert-subject",
> diff --git a/hmp.c b/hmp.c
> index b47f331..df9736c 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -1140,6 +1140,13 @@ void hmp_migrate_set_capability(Monitor *mon, const QDict *qdict)
>      }
>  }
>  
> +void hmp_migrate_start_postcopy(Monitor *mon, const QDict *qdict)
> +{
> +    Error *err = NULL;
> +    qmp_migrate_start_postcopy(&err);
> +    hmp_handle_error(mon, &err);
> +}
> +
>  void hmp_set_password(Monitor *mon, const QDict *qdict)
>  {
>      const char *protocol  = qdict_get_str(qdict, "protocol");
> diff --git a/hmp.h b/hmp.h
> index 4bb5dca..da1334f 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -64,6 +64,7 @@ void hmp_migrate_set_downtime(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_set_speed(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_set_capability(Monitor *mon, const QDict *qdict);
>  void hmp_migrate_set_cache_size(Monitor *mon, const QDict *qdict);
> +void hmp_migrate_start_postcopy(Monitor *mon, const QDict *qdict);
>  void hmp_set_password(Monitor *mon, const QDict *qdict);
>  void hmp_expire_password(Monitor *mon, const QDict *qdict);
>  void hmp_eject(Monitor *mon, const QDict *qdict);
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index e6a814a..293c83e 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -104,6 +104,9 @@ struct MigrationState
>      int64_t xbzrle_cache_size;
>      int64_t setup_time;
>      int64_t dirty_sync_count;
> +
> +    /* Flag set once the migration has been asked to enter postcopy */
> +    bool start_postcopy;
>  };
>  
>  void process_incoming_migration(QEMUFile *f);
> diff --git a/migration/migration.c b/migration/migration.c
> index a4fc7d7..43ca656 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -372,6 +372,28 @@ void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
>      }
>  }
>  
> +void qmp_migrate_start_postcopy(Error **errp)
> +{
> +    MigrationState *s = migrate_get_current();
> +
> +    if (!migrate_postcopy_ram()) {
> +        error_setg(errp, "Enable postcopy with migration_set_capability before"
> +                         " the start of migration");
> +        return;
> +    }
> +
> +    if (s->state == MIG_STATE_NONE) {
> +        error_setg(errp, "Postcopy must be started after migration has been"
> +                         " started");
> +        return;
> +    }
> +    /*
> +     * we don't error if migration has finished since that would be racy
> +     * with issuing this command.
> +     */
> +    atomic_set(&s->start_postcopy, true);

Why atomic_set?

> +}
> +
>  /* shared migration helpers */
>  
>  static void migrate_set_state(MigrationState *s, int old_state, int new_state)
> diff --git a/qapi-schema.json b/qapi-schema.json
> index a8af1cb..7ff61e9 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -542,6 +542,14 @@
>  { 'command': 'query-migrate-capabilities', 'returns':   ['MigrationCapabilityStatus']}
>  
>  ##
> +# @migrate-start-postcopy
> +#
> +# Switch migration to postcopy mode
> +#
> +# Since: 2.3
> +{ 'command': 'migrate-start-postcopy' }
> +
> +##
>  # @MouseInfo:
>  #
>  # Information about a mouse device.
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index a85d847..25d2208 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -685,6 +685,25 @@ Example:
>  
>  EQMP
>      {
> +        .name       = "migrate-start-postcopy",
> +        .args_type  = "",
> +        .mhandler.cmd_new = qmp_marshal_input_migrate_start_postcopy,
> +    },
> +
> +SQMP
> +migrate-start-postcopy
> +----------------------
> +
> +Switch an in-progress migration to postcopy mode. Ignored after the end of
> +migration (or once already in postcopy).
> +
> +Example:
> +-> { "execute": "migrate-start-postcopy" }
> +<- { "return": {} }
> +
> +EQMP
> +
> +    {
>          .name       = "query-migrate-cache-size",
>          .args_type  = "",
>          .mhandler.cmd_new = qmp_marshal_input_query_migrate_cache_size,

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson