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

[Peter Xu <peterx@redhat.com>]

On Thu, Mar 01, 2018 at 03:32:19PM +0000, Dr. David Alan Gilbert wrote:
> * 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 :-)

Ah sure. :)

Please just let me know if you want me to post a patch, or I'll assume
you'll handle this together in the next post (and thanks anyways :)

-- 
Peter Xu