Re: [Qemu-devel] [PATCH] migration: Fix block failure cases

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

* Peter Xu (peterx@redhat.com) wrote:
> On Wed, Feb 28, 2018 at 04:49:37PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > 
> > This fixes a couple of cases where the block migration capability
> > doesn't get cleared when a migration failed.
> > 
> > 1) When block migration is compiled out:
> >   (qemu) migrate -d -b  "exec:cat > /dev/null"
> >   QEMU compiled without old-style (blk/-b, inc/-i) block migration
> >   Use drive_mirror+NBD instead.
> >   (qemu) migrate_set_capability xbzrle off
> >   QEMU compiled without old-style (blk/-b, inc/-i) block migration
> >   Use drive_mirror+NBD instead.
> > 
> >   This corresponds to https://bugzilla.redhat.com/show_bug.cgi?id=1550022
> > 
> > 2) When a migration with a bad protocol is tried:
> >   (qemu) migrate -d -b "foo:bah"
> >   Parameter 'uri' expects a valid migration protocol
> >   (qemu) info migrate_capabilities
> >   xbzrle: off
> >   rdma-pin-all: off
> >   auto-converge: off
> >   zero-blocks: off
> >   compress: off
> >   events: off
> >   postcopy-ram: off
> >   x-colo: off
> >   release-ram: off
> >   block: on   <<<<<<-----
> >   return-path: off
> >   pause-before-switchover: off
> >   x-multifd: off
> > 
> > Fixes: 2833c59b947
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> >  migration/migration.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/migration/migration.c b/migration/migration.c
> > index b913b98803..da0e4a1f56 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1391,11 +1391,12 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
> >              return;
> >          }
> >          migrate_set_block_enabled(true, &local_err);
> > +        s->must_remove_block_options = true;
> >          if (local_err) {
> >              error_propagate(errp, local_err);
> > +            block_cleanup_parameters(s);
> >              return;
> >          }
> > -        s->must_remove_block_options = true;
> >      }
> >  
> >      if (has_inc && inc) {
> > @@ -1417,11 +1418,10 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
> >      } else if (strstart(uri, "fd:", &p)) {
> >          fd_start_outgoing_migration(s, p, &local_err);
> >      } else {
> > -        error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "uri",
> > +        error_setg(&local_err, QERR_INVALID_PARAMETER_VALUE, "uri",
> >                     "a valid migration protocol");
> >          migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
> >                            MIGRATION_STATUS_FAILED);
> > -        return;
> >      }
> >  
> >      if (local_err) {
> > -- 
> > 2.14.3
> > 
> 
> Ouch...
> 
> Instead it seems to be my fault in 4a84214ebe ("migration: provide
> migrate_caps_check()", 2017-07-18).  For now I cannot understand why I
> did that before since it's obviously strange if without this
> squashed...
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 0aa596f867..88ed9375aa 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -747,13 +747,15 @@ void qmp_migrate_set_capabilities(MigrationCapabilityStatusList *params,
>  {
>      MigrationState *s = migrate_get_current();
>      MigrationCapabilityStatusList *cap;
> +    bool cap_list[MIGRATION_CAPABILITY__MAX];
>  
>      if (migration_is_setup_or_active(s->state)) {
>          error_setg(errp, QERR_MIGRATION_ACTIVE);
>          return;
>      }
>  
> -    if (!migrate_caps_check(s->enabled_capabilities, params, errp)) {
> +    memcpy(cap_list, s->enabled_capabilities, sizeof(cap_list));
> +    if (!migrate_caps_check(cap_list, params, errp)) {
>          return;
>      }

> 
> Otherwise I'll get:
> 
> (qemu) migrate_set_capability postcopy-ram on                                  
> (qemu) migrate_set_capability compress on                                      
> Postcopy is not currently compatible with compression                          
> (qemu) info migrate_capabilities       
> xbzrle: off                            
> rdma-pin-all: off                      
> auto-converge: off                     
> zero-blocks: off                       
> compress: on         <------------------------- :(
> events: off                            
> postcopy-ram: on                       
> x-colo: off                            
> release-ram: off                       
> block: off                             
> return-path: off                       
> pause-before-switchover: off           
> x-multifd: off
>  
> And it looks very likely that this should solve the block bug too.

Yes, it looks like it should - but it doesn't solve the 2nd of my cases;
so we also need the 2nd half of my change.

> (So I think either I got a brain fart last July, or now...)

Of course it's the combination of two bugs :-)

Dave

> Thanks,
> 
> -- 
> Peter Xu
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK