Re: [Xen-devel] [PATCH v8 --for 4.6 COLO 05/25] tools/libxl: add back channel support to write stream

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/07/15 10:18, Yang Hongyang wrote:
> Add back channel support to write stream. If the write stream is
> a back channel stream, this means the write stream is used by
> Secondary to send some records back.
>
> Signed-off-by: Yang Hongyang <yanghy@xxxxxxxxxxxxxx>
> ---
>  tools/libxl/libxl_dom_save.c     |  1 +
>  tools/libxl/libxl_internal.h     |  1 +
>  tools/libxl/libxl_stream_write.c | 16 ++++++++++++++++
>  3 files changed, 18 insertions(+)
>
> diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
> index 9b7159f..25813ce 100644
> --- a/tools/libxl/libxl_dom_save.c
> +++ b/tools/libxl/libxl_dom_save.c
> @@ -445,6 +445,7 @@ void libxl__domain_save(libxl__egc *egc, 
> libxl__domain_save_state *dss)
>      dss->sws.ao  = dss->ao;
>      dss->sws.dss = dss;
>      dss->sws.fd  = dss->fd;
> +    dss->sws.back_channel = false;
>      dss->sws.completion_callback = stream_done;
>  
>      libxl__stream_write_start(egc, &dss->sws);
> diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
> index 9c81d8d..a83d6a5 100644
> --- a/tools/libxl/libxl_internal.h
> +++ b/tools/libxl/libxl_internal.h
> @@ -2989,6 +2989,7 @@ struct libxl__stream_write_state {
>      libxl__ao *ao;
>      libxl__domain_save_state *dss;
>      int fd;
> +    bool back_channel;
>      void (*completion_callback)(libxl__egc *egc,
>                                  libxl__stream_write_state *sws,
>                                  int rc);
> diff --git a/tools/libxl/libxl_stream_write.c 
> b/tools/libxl/libxl_stream_write.c
> index 16f667a..df55277 100644
> --- a/tools/libxl/libxl_stream_write.c
> +++ b/tools/libxl/libxl_stream_write.c
> @@ -47,6 +47,13 @@
>   *  - Toolstack record
>   *  - if (hvm), Qemu record
>   *  - Checkpoint end record
> + *
> + * For back channel stream:
> + * - libxl__stream_write_start()
> + *    - Set up the stream to running state
> + *
> + * - Add a new API to write the record. When the record is written
> + *   out, call stream->checkpoint_callback() to return.
>   */
>  
>  /* Success/error/cleanup handling. */
> @@ -178,6 +185,9 @@ void libxl__stream_write_start(libxl__egc *egc,
>  
>      stream->running = true;
>  
> +    if (stream->back_channel)
> +        return;
> +

Some of the setup below should not be skipped.

While it makes the diff bigger, the end result would be more logical as

dc->ao = ao;
dc->readfd = -1;
dc->writefd = stream->fd;
dc->maxsz = -1;

if (!stream->back_channel) {
    /* Write the stream header. */
    dc->writewhat = "save/migration stream";
    dc->callback = stream_header_done;

    rc = ibxl__datacopier_start(dc);
    ....
}

To split the object setup from the action of sending the stream header,
which are currently mixed.

What happened to the backchannel negotiation header?

~Andrew

>      dc->ao        = ao;
>      dc->readfd    = -1;
>      dc->writewhat = "save/migration stream";
> @@ -207,6 +217,7 @@ void libxl__stream_write_start_checkpoint(libxl__egc *egc,
>  {
>      assert(stream->running);
>      assert(!stream->in_checkpoint);
> +    assert(!stream->back_channel);
>      stream->in_checkpoint = true;
>  
>      write_toolstack_record(egc, stream);
> @@ -500,6 +511,11 @@ static void stream_done(libxl__egc *egc,
>      assert(stream->running);
>      stream->running = false;
>  
> +    if (stream->back_channel) {
> +        stream->completion_callback(egc, stream, stream->rc);
> +        return;
> +    }
> +
>      if (stream->emu_carefd)
>          libxl__carefd_close(stream->emu_carefd);
>      free(stream->emu_body);


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