Re: [Qemu-devel] [PATCH] migration: introduce migrate_is_blocked()

[Paolo Bonzini]

On 04/05/2016 21:44, Greg Kurz wrote:
> QEMU has currently two ways to prevent migration to occur:
> - migration blocker when it depends on runtime state
> - VMStateDescription.unmigratable when migration is not supported at all
> 
> This patch gathers all the logic into a single function to be called from
> both the savevm and the migrate paths.
> 
> This fixes a bug with 9p, at least, where savevm would succeed and the
> following would happen in the guest after loadvm:
> 
> $ ls /host
> ls: cannot access /host: Protocol error
> 
> With this patch:
> 
> (qemu) savevm foo
> Migration is disabled when VirtFS export path '/' is mounted in the guest
> using mount_tag 'host'
> 
> Signed-off-by: Greg Kurz <address@hidden>
> ---
> 
> Since there has been some activity on 9p again since a few weeks, maybe it
> is not too late for 2.6, if everybody agrees the fix is ok ?

The patch is good, but I think the subject should be

    savevm: fail if migration blockers are present

The subject you used would be good for the include/migration and
migration/migration.c parts alone (where you introduce the function
without any semantic change).

Apart from this,

Reviewed-by: Paolo Bonzini <address@hidden>

Thanks,

Paolo

>  include/migration/migration.h |    1 +
>  migration/migration.c         |   21 +++++++++++++++------
>  migration/savevm.c            |    2 +-
>  3 files changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index ac2c12c2a518..9e36a97fc5e5 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -210,6 +210,7 @@ int migrate_fd_close(MigrationState *s);
>  void add_migration_state_change_notifier(Notifier *notify);
>  void remove_migration_state_change_notifier(Notifier *notify);
>  MigrationState *migrate_init(const MigrationParams *params);
> +bool migration_is_blocked(Error **errp);
>  bool migration_in_setup(MigrationState *);
>  bool migration_has_finished(MigrationState *);
>  bool migration_has_failed(MigrationState *);
> diff --git a/migration/migration.c b/migration/migration.c
> index 991313a8629a..afd883b78179 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -992,6 +992,20 @@ void qmp_migrate_incoming(const char *uri, Error **errp)
>      once = false;
>  }
>  
> +bool migration_is_blocked(Error **errp)
> +{
> +    if (qemu_savevm_state_blocked(errp)) {
> +        return true;
> +    }
> +
> +    if (migration_blockers) {
> +        *errp = error_copy(migration_blockers->data);
> +        return true;
> +    }
> +
> +    return false;
> +}
> +
>  void qmp_migrate(const char *uri, bool has_blk, bool blk,
>                   bool has_inc, bool inc, bool has_detach, bool detach,
>                   Error **errp)
> @@ -1014,12 +1028,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool 
> blk,
>          return;
>      }
>  
> -    if (qemu_savevm_state_blocked(errp)) {
> -        return;
> -    }
> -
> -    if (migration_blockers) {
> -        *errp = error_copy(migration_blockers->data);
> +    if (migration_is_blocked(errp)) {
>          return;
>      }
>  
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 16ba44379870..834664936dfc 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1169,7 +1169,7 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
>      MigrationState *ms = migrate_init(&params);
>      ms->to_dst_file = f;
>  
> -    if (qemu_savevm_state_blocked(errp)) {
> +    if (migration_is_blocked(errp)) {
>          return -EINVAL;
>      }
>  
> 
> 
>