Re: [Qemu-devel] [RFC 24/29] migration: new message MIG_RP_MSG_RESUME_ACK

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

* Peter Xu (peterx@redhat.com) wrote:
> Creating new message to reply for MIG_CMD_POSTCOPY_RESUME. One uint32_t
> is used as payload to let the source know whether destination is ready
> to continue the migration.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/migration.c  | 37 +++++++++++++++++++++++++++++++++++++
>  migration/migration.h  |  1 +
>  migration/savevm.c     |  3 ++-
>  migration/trace-events |  1 +
>  4 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index c2b85ac..62f91ce 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -93,6 +93,7 @@ enum mig_rp_message_type {
>      MIG_RP_MSG_REQ_PAGES_ID, /* data (start: be64, len: be32, id: string) */
>      MIG_RP_MSG_REQ_PAGES,    /* data (start: be64, len: be32) */
>      MIG_RP_MSG_RECV_BITMAP,  /* send recved_bitmap back to source */
> +    MIG_RP_MSG_RESUME_ACK,   /* tell source that we are ready to resume */
>  
>      MIG_RP_MSG_MAX
>  };
> @@ -484,6 +485,14 @@ void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
>      trace_migrate_send_rp_recv_bitmap(block_name, res);
>  }
>  
> +void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value)
> +{
> +    uint32_t buf;
> +
> +    buf = cpu_to_be32(value);
> +    migrate_send_rp_message(mis, MIG_RP_MSG_RESUME_ACK, sizeof(buf), &buf);
> +}
> +
>  MigrationCapabilityStatusList *qmp_query_migrate_capabilities(Error **errp)
>  {
>      MigrationCapabilityStatusList *head = NULL;
> @@ -1595,6 +1604,7 @@ static struct rp_cmd_args {
>      [MIG_RP_MSG_REQ_PAGES]      = { .len = 12, .name = "REQ_PAGES" },
>      [MIG_RP_MSG_REQ_PAGES_ID]   = { .len = -1, .name = "REQ_PAGES_ID" },
>      [MIG_RP_MSG_RECV_BITMAP]    = { .len = -1, .name = "RECV_BITMAP" },
> +    [MIG_RP_MSG_RESUME_ACK]     = { .len =  4, .name = "RESUME_ACK" },
>      [MIG_RP_MSG_MAX]            = { .len = -1, .name = "MAX" },
>  };
>  
> @@ -1652,6 +1662,25 @@ static int migrate_handle_rp_recv_bitmap(MigrationState *s, char *block_name)
>      return ram_dirty_bitmap_reload(s, block);
>  }
>  
> +static int migrate_handle_rp_resume_ack(MigrationState *s, uint32_t value)
> +{
> +    trace_source_return_path_thread_resume_ack(value);
> +
> +    /*
> +     * Currently value will always be one. It can be used in the
> +     * future to notify source that destination cannot continue.
> +     */
> +    assert(value == 1);

Again I prefer the routine to fail than to assert.
Maybe it's worth having a constant rather than the magic 1.


> +    /* Now both sides are active. */
> +    migrate_set_state(&s->state, MIGRATION_STATUS_POSTCOPY_RECOVER,
> +                      MIGRATION_STATUS_POSTCOPY_ACTIVE);
> +
> +    /* TODO: notify send thread that time to continue send pages */
> +
> +    return 0;
> +}
> +
>  /*
>   * Handles messages sent on the return path towards the source VM
>   *
> @@ -1771,6 +1800,14 @@ retry:
>              }
>              break;
>  
> +        case MIG_RP_MSG_RESUME_ACK:
> +            tmp32 = ldl_be_p(buf);
> +            if (migrate_handle_rp_resume_ack(ms, tmp32)) {
> +                mark_source_rp_bad(ms);
> +                goto out;
> +            }
> +            break;
> +
>          default:
>              break;
>          }
> diff --git a/migration/migration.h b/migration/migration.h
> index 4d38308..2a3f905 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -206,5 +206,6 @@ int migrate_send_rp_req_pages(MigrationIncomingState *mis, const char* rbname,
>                                ram_addr_t start, size_t len);
>  void migrate_send_rp_recv_bitmap(MigrationIncomingState *mis,
>                                   char *block_name);
> +void migrate_send_rp_resume_ack(MigrationIncomingState *mis, uint32_t value);
>  
>  #endif
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 2e330bc..02a67ac 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1690,7 +1690,8 @@ static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
>                        MIGRATION_STATUS_POSTCOPY_ACTIVE);
>      qemu_sem_post(&mis->postcopy_pause_sem_fault);
>  
> -    /* TODO: Tell source that "we are ready" */
> +    /* Tell source that "we are ready" */
> +    migrate_send_rp_resume_ack(mis, 1);
>  
>      return 0;
>  }
> diff --git a/migration/trace-events b/migration/trace-events
> index 04dd9d8..0b43fec 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -116,6 +116,7 @@ source_return_path_thread_entry(void) ""
>  source_return_path_thread_loop_top(void) ""
>  source_return_path_thread_pong(uint32_t val) "%x"
>  source_return_path_thread_shut(uint32_t val) "%x"
> +source_return_path_thread_resume_ack(uint32_t v) "%"PRIu32
>  migrate_global_state_post_load(const char *state) "loaded state: %s"
>  migrate_global_state_pre_save(const char *state) "saved state: %s"
>  migration_thread_low_pending(uint64_t pending) "%" PRIu64
> -- 
> 2.7.4

Dave

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