Re: [Qemu-devel] [PATCH v7 14/42] Return path: Send responses from destination to source

[Juan Quintela]

"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> "Dr. David Alan Gilbert (git)" <address@hidden> wrote:
>> > From: "Dr. David Alan Gilbert" <address@hidden>
>> >
>> > Add migrate_send_rp_message to send a message from destination to source 
>> > along the return path.
>> >   (It uses a mutex to let it be called from multiple threads)
>> > Add migrate_send_rp_shut to send a 'shut' message to indicate
>> >   the destination is finished with the RP.
>> > Add migrate_send_rp_ack to send a 'PONG' message in response to a PING
>> >   Use it in the MSG_RP_PING handler
>> >
>> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>> > ---
>> >  include/migration/migration.h | 17 ++++++++++++++++
>> >  migration/migration.c         | 45 
>> > +++++++++++++++++++++++++++++++++++++++++++
>> >  migration/savevm.c            |  2 +-
>> >  trace-events                  |  1 +
>> >  4 files changed, 64 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/include/migration/migration.h b/include/migration/migration.h
>> > index 65fe5db..36caab9 100644
>> > --- a/include/migration/migration.h
>> > +++ b/include/migration/migration.h
>> > @@ -42,12 +42,20 @@ struct MigrationParams {
>> >      bool shared;
>> >  };
>> >  
>> > +/* Messages sent on the return path from destination to source */
>> > +enum mig_rp_message_type {
>> > +    MIG_RP_MSG_INVALID = 0,  /* Must be 0 */
>> > +    MIG_RP_MSG_SHUT,         /* sibling will not send any more RP 
>> > messages */
>> > +    MIG_RP_MSG_PONG,         /* Response to a PING; data (seq: be32 ) */
>> > +};
>> > +
>> >  typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
>> >  /* State for the incoming migration */
>> >  struct MigrationIncomingState {
>> >      QEMUFile *file;
>> >  
>> >      QEMUFile *return_path;
>> > +    QemuMutex      rp_mutex;    /* We send replies from multiple threads 
>> > */
>> >  
>> >      /* See savevm.c */
>> >      LoadStateEntry_Head loadvm_handlers;
>> > @@ -179,6 +187,15 @@ int migrate_compress_level(void);
>> >  int migrate_compress_threads(void);
>> >  int migrate_decompress_threads(void);
>> >  
>> > +/* Sending on the return path - generic and then for each message type */
>> > +void migrate_send_rp_message(MigrationIncomingState *mis,
>> > +                             enum mig_rp_message_type message_type,
>> > +                             uint16_t len, void *data);
>> > +void migrate_send_rp_shut(MigrationIncomingState *mis,
>> > +                          uint32_t value);
>> > +void migrate_send_rp_pong(MigrationIncomingState *mis,
>> > +                          uint32_t value);
>> > +
>> >  void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
>> >  void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
>> >  void ram_control_load_hook(QEMUFile *f, uint64_t flags);
>> > diff --git a/migration/migration.c b/migration/migration.c
>> > index 295f15a..afb19a1 100644
>> > --- a/migration/migration.c
>> > +++ b/migration/migration.c
>> > @@ -85,6 +85,7 @@ MigrationIncomingState 
>> > *migration_incoming_state_new(QEMUFile* f)
>> >      mis_current = g_malloc0(sizeof(MigrationIncomingState));
>> >      mis_current->file = f;
>> >      QLIST_INIT(&mis_current->loadvm_handlers);
>> > +    qemu_mutex_init(&mis_current->rp_mutex);
>> >  
>> >      return mis_current;
>> >  }
>> > @@ -182,6 +183,50 @@ void process_incoming_migration(QEMUFile *f)
>> >      qemu_coroutine_enter(co, f);
>> >  }
>> >  
>> > +/*
>> > + * Send a message on the return channel back to the source
>> > + * of the migration.
>> > + */
>> > +void migrate_send_rp_message(MigrationIncomingState *mis,
>> > +                             enum mig_rp_message_type message_type,
>> > +                             uint16_t len, void *data)
>> > +{
>> > +    trace_migrate_send_rp_message((int)message_type, len);
>> > +    qemu_mutex_lock(&mis->rp_mutex);
>> > +    qemu_put_be16(mis->return_path, (unsigned int)message_type);
>> > +    qemu_put_be16(mis->return_path, len);
>> if (len) {
>> 
>> > +    qemu_put_buffer(mis->return_path, data, len);
>> }
>> 
>> 
>> ?
>> 
>> We check for zero sized command on control commands but not on
>> responses?
>
> Or should I remove the check in the control commands case?
> qemu_put_buffer looks like it's safe for size == 0

I would go for this just for consistence?