Re: [Xen-devel] [PATCH v10 10/31] tools/libxl: add back channel support to write stream

[Wen Congyang <wency@xxxxxxxxxxxxxx>]

On 02/25/2016 11:54 PM, Wei Liu wrote:
> On Mon, Feb 22, 2016 at 10:52:14AM +0800, Wen Congyang 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 <hongyang.yang@xxxxxxxxxxxx>
>> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
>> ---
>>  tools/libxl/libxl_dom_save.c     |  1 +
>>  tools/libxl/libxl_internal.h     |  1 +
>>  tools/libxl/libxl_stream_write.c | 26 ++++++++++++++++++++------
>>  3 files changed, 22 insertions(+), 6 deletions(-)
>>
>> diff --git a/tools/libxl/libxl_dom_save.c b/tools/libxl/libxl_dom_save.c
>> index 72b61c7..18946c5 100644
>> --- a/tools/libxl/libxl_dom_save.c
>> +++ b/tools/libxl/libxl_dom_save.c
>> @@ -404,6 +404,7 @@ 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 3d3e8e8..e02e554 100644
>> --- a/tools/libxl/libxl_internal.h
>> +++ b/tools/libxl/libxl_internal.h
>> @@ -3044,6 +3044,7 @@ 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 f6ea55d..5379126 100644
>> --- a/tools/libxl/libxl_stream_write.c
>> +++ b/tools/libxl/libxl_stream_write.c
>> @@ -49,6 +49,13 @@
>>   *  - if (hvm)
>>   *      - Emulator context 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.
> 
> What does this mean? Which new API?

The next patch introduces this API. The commits is very old.

I think I can merge these two patches into one patch.

> 
>>   */
>>  
>>  /* Success/error/cleanup handling. */
>> @@ -225,6 +232,15 @@ void libxl__stream_write_start(libxl__egc *egc,
>>  
>>      stream->running = true;
>>  
>> +    dc->ao        = ao;
>> +    dc->readfd    = -1;
>> +    dc->copywhat  = "save v2 stream";
>> +    dc->writefd   = stream->fd;
>> +    dc->maxsz     = -1;
>> +
>> +    if (stream->back_channel)
>> +        return;
>> +
> 
> There seems to be very subtle change of behaviour.
> 
> Before this patch, the dc->* are not set until the emulator check is
> done. With this path, it is possible in the normal case some of the
> fields are initialised in the error path.
> 
> I think this is OK given the callbacks in the upper layer and in
> the writer don't rely on those fields to clean up. Just one thing to
> note.
> 
> That said, I suggest you move all initialisation of dc->* in one place.

OK, I will do it.

> 
>>      if (dss->type == LIBXL_DOMAIN_TYPE_HVM) {
>>          stream->device_model_version =
>>              libxl__device_model_version_running(gc, dss->domid);
>> @@ -249,12 +265,7 @@ void libxl__stream_write_start(libxl__egc *egc,
>>          stream->emu_sub_hdr.index = 0;
>>      }
>>  
>> -    dc->ao        = ao;
>> -    dc->readfd    = -1;
>>      dc->writewhat = "stream header";
>> -    dc->copywhat  = "save v2 stream";
>> -    dc->writefd   = stream->fd;
>> -    dc->maxsz     = -1;
>>      dc->callback  = stream_header_done;
>>  
>>      rc = libxl__datacopier_start(dc);
>> @@ -279,6 +290,7 @@ 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_emulator_xenstore_record(egc, stream);
>> @@ -590,7 +602,9 @@ static void stream_done(libxl__egc *egc,
>>          libxl__carefd_close(stream->emu_carefd);
>>      free(stream->emu_body);
>>  
>> -    check_all_finished(egc, stream, rc);
>> +    if (!stream->back_channel)
>> +        /* back channel stream doesn't have save helper */
>> +        check_all_finished(egc, stream, rc);
> 
> Though it doesn't have helper, do you not need to check if the back
> channel stream itself is OK? The comment itself doesn't seem to justify
> this change.

What do you want to check? assert(!stream->shs) or 
assert(!libxl__stream_write_inuse(stream))?

Thanks
Wen Congyang

> 
> Wei.
> 
>>  }
>>  
>>  static void checkpoint_done(libxl__egc *egc,
>> -- 
>> 2.5.0
>>
>>
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxx
>> http://lists.xen.org/xen-devel
> 
> 
> .
> 




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel