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

[Greg Kurz]

On Wed, 11 May 2016 13:59:19 +0200
Paolo Bonzini <address@hidden> wrote:

> 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).
> 

Yeah, I agree the subject you are suggesting is far more informative :)

> Apart from this,
> 
> Reviewed-by: Paolo Bonzini <address@hidden>
> 

Thanks for the review !

> Thanks,
> 
> Paolo
> 

Cheers.

--
Greg

> >  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;
> >      }
> >  
> > 
> > 
> >   
>