Re: [Qemu-devel] [RFC PATCH 04/17] COLO info: use colo info to tell migration target colo is enabled

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

* Yang Hongyang (yanghy@cn.fujitsu.com) wrote:
> migrate colo info to migration target to tell the target colo is
> enabled.

If I understand this correctly this means that you send a 'colo info' device
information for migrations that don't have COLO enabled; that's bad because
it breaks migration unless the destination has it; I guess it's OK if you
were to guard it with a thing so it didn't do it for old machine-types.

You could use the QEMU_VM_COMMAND sections I've created for postcopy;
( http://lists.gnu.org/archive/html/qemu-devel/2014-07/msg00889.html ) and 
add a QEMU_VM_CMD_COLO to indicate you want the destination to become an SVM,
  then check the capability near the start of migration and send the command.

Or perhaps there's a way to add the colo-info device on the command line so it's
not always there.

Dave

> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
> ---
>  Makefile.objs                      |  1 +
>  include/migration/migration-colo.h |  3 ++
>  migration-colo-comm.c              | 68 ++++++++++++++++++++++++++++++++++++++
>  vl.c                               |  4 +++
>  4 files changed, 76 insertions(+)
>  create mode 100644 migration-colo-comm.c
> 
> diff --git a/Makefile.objs b/Makefile.objs
> index cab5824..1836a68 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -50,6 +50,7 @@ common-obj-$(CONFIG_POSIX) += os-posix.o
>  common-obj-$(CONFIG_LINUX) += fsdev/
>  
>  common-obj-y += migration.o migration-tcp.o
> +common-obj-y += migration-colo-comm.o
>  common-obj-$(CONFIG_COLO) += migration-colo.o
>  common-obj-y += vmstate.o
>  common-obj-y += qemu-file.o
> diff --git a/include/migration/migration-colo.h b/include/migration/migration-colo.h
> index 35b384c..e3735d8 100644
> --- a/include/migration/migration-colo.h
> +++ b/include/migration/migration-colo.h
> @@ -12,6 +12,9 @@
>  #define QEMU_MIGRATION_COLO_H
>  
>  #include "qemu-common.h"
> +#include "migration/migration.h"
> +
> +void colo_info_mig_init(void);
>  
>  bool colo_supported(void);
>  
> diff --git a/migration-colo-comm.c b/migration-colo-comm.c
> new file mode 100644
> index 0000000..ccbc246
> --- /dev/null
> +++ b/migration-colo-comm.c
> @@ -0,0 +1,68 @@
> +/*
> + *  COarse-grain LOck-stepping Virtual Machines for Non-stop Service (COLO)
> + *  (a.k.a. Fault Tolerance or Continuous Replication)
> + *
> + *  Copyright (C) 2014 FUJITSU LIMITED
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or
> + * later.  See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include <migration/migration-colo.h>
> +
> +#define DEBUG_COLO
> +
> +#ifdef DEBUG_COLO
> +#define DPRINTF(fmt, ...) \
> +    do { fprintf(stdout, "COLO: " fmt, ## __VA_ARGS__); } while (0)
> +#else
> +#define DPRINTF(fmt, ...) \
> +    do { } while (0)
> +#endif
> +
> +static bool colo_requested;
> +
> +/* save */
> +
> +static bool migrate_use_colo(void)
> +{
> +    MigrationState *s = migrate_get_current();
> +    return s->enabled_capabilities[MIGRATION_CAPABILITY_COLO];
> +}
> +
> +static void colo_info_save(QEMUFile *f, void *opaque)
> +{
> +    qemu_put_byte(f, migrate_use_colo());
> +}
> +
> +/* restore */
> +
> +static int colo_info_load(QEMUFile *f, void *opaque, int version_id)
> +{
> +    int value = qemu_get_byte(f);
> +
> +    if (value && !colo_supported()) {
> +        fprintf(stderr, "COLO is not supported\n");
> +        return -EINVAL;
> +    }
> +
> +    if (value && !colo_requested) {
> +        DPRINTF("COLO requested!\n");
> +    }
> +
> +    colo_requested = value;
> +
> +    return 0;
> +}
> +
> +static SaveVMHandlers savevm_colo_info_handlers = {
> +    .save_state = colo_info_save,
> +    .load_state = colo_info_load,
> +};
> +
> +void colo_info_mig_init(void)
> +{
> +    register_savevm_live(NULL, "colo info", -1, 1,
> +                         &savevm_colo_info_handlers, NULL);
> +}
> diff --git a/vl.c b/vl.c
> index fe451aa..1a282d8 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -89,6 +89,7 @@ int main(int argc, char **argv)
>  #include "sysemu/dma.h"
>  #include "audio/audio.h"
>  #include "migration/migration.h"
> +#include "migration/migration-colo.h"
>  #include "sysemu/kvm.h"
>  #include "qapi/qmp/qjson.h"
>  #include "qemu/option.h"
> @@ -4339,6 +4340,9 @@ int main(int argc, char **argv, char **envp)
>  
>      blk_mig_init();
>      ram_mig_init();
> +    if (colo_supported()) {
> +        colo_info_mig_init();
> +    }
>  
>      /* open the virtual block devices */
>      if (snapshot)
> -- 
> 1.9.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK