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

[Yang Hongyang <yanghy@xxxxxxxxxxxxxx>]

On 07/16/2015 01:25 AM, Andrew Cooper wrote:
> 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?
There's no negotiation header currently...If it is a broken back channel,
COLO will fail.

> ~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);
> .
--
Thanks,
Yang.

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