Re: [Qemu-devel] [PATCH v5 23/45] migrate_start_postcopy: Command to trigger transition to postcopy

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* David Gibson (david@gibson.dropbear.id.au) wrote:
> 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?

It's being read by the migration thread, this is happening in the main thread.

There's no strict ordering requirement or anything.

Dave

> 
> > +}
> > +
> >  /* 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


--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK