Re: [PATCH 1/5] remus: don't call stream_continue() when doing failover

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 30/12/2015 01:39, Wen Congyang wrote:
> stream_continue() is used for migration to read emulator
> xenstore data and emulator context. For remus, if we do
> failover, we have read it in the checkpoint cycle, and
> we only need to complete the stream.
>
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>, with one suggestion

> ---
>   tools/libxl/libxl_stream_read.c | 18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/tools/libxl/libxl_stream_read.c b/tools/libxl/libxl_stream_read.c
> index 258dec4..42c087f 100644
> --- a/tools/libxl/libxl_stream_read.c
> +++ b/tools/libxl/libxl_stream_read.c
> @@ -758,6 +758,9 @@ void libxl__xc_domain_restore_done(libxl__egc *egc, void *dcs_void,
>       libxl__stream_read_state *stream = &dcs->srs;
>       STATE_AO_GC(dcs->ao);
>   
> +    /* convenience aliases */
> +    const int checkpointed_stream = dcs->restore_params.checkpointed_stream;
> +
>       if (rc)
>           goto err;
>   
> @@ -777,11 +780,16 @@ void libxl__xc_domain_restore_done(libxl__egc *egc, void *dcs_void,
>        * If the stream is not still alive, we must not continue any work.
>        */
>       if (libxl__stream_read_inuse(stream)) {
> -        /*
> -         * Libxc has indicated that it is done with the stream.  Resume reading
> -         * libxl records from it.
> -         */
> -        stream_continue(egc, stream);
> +        if (checkpointed_stream) {
> +            /* failover */

I would recommend extending this comment to include the information in 
the commit message.  Something like:

/* Failover from primary.  Domain state is currently at a consistent 
checkpoint, ready to go. */

> +            stream_complete(egc, stream, 0);
> +        } else {
> +            /*
> +             * Libxc has indicated that it is done with the stream.
> +             * Resume reading libxl records from it.
> +             */
> +            stream_continue(egc, stream);
> +        }
>       }
>   }
>