Re: [Xen-devel] [PATCH v3 2/5] remus: resume immediately if libxl__xc_domain_save_done() completes

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2016-01-12 at 09:40 +0800, Wen Congyang wrote:
> On 01/09/2016 12:27 AM, Ian Campbell wrote:
> > On Fri, 2016-01-08 at 14:38 +0800, Wen Congyang wrote:
> > > For example: if the secondary host is down, and we fail to send the
> > > data
> > > to
> > > the secondary host. xc_domain_save() returns 0.
> > 
> > Just to be check: On failure in this way xc_domain_save() returns 0
> > (i.e.
> > success)?
> 
> Yes, it returns 0. I am not sure the return value is right.
> 
> > 
> > > ÂSo in the function
> > > libxl__xc_domain_save_done(), rc is 0(the helper program exits
> > > normally),
> > > and retval is 0(it is xc_domain_save()'s return value). In such case,
> > > we
> > > just need to complete the stream.
> > > 
> > > Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> > > ---
> > > Âtools/libxl/libxl_stream_write.c | 13 +++++++++++--
> > > Â1 file changed, 11 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/tools/libxl/libxl_stream_write.c
> > > b/tools/libxl/libxl_stream_write.c
> > > index 80d9208..82e7719 100644
> > > --- a/tools/libxl/libxl_stream_write.c
> > > +++ b/tools/libxl/libxl_stream_write.c
> > > @@ -354,8 +354,17 @@ void libxl__xc_domain_save_done(libxl__egc *egc,
> > > void *dss_void,
> > > ÂÂÂÂÂÂ* alive, and check_all_finished() may have torn it down around
> > > us.
> > > ÂÂÂÂÂÂ* If the stream is not still alive, we must not continue any
> > > work.
> > > ÂÂÂÂÂÂ*/
> > > -ÂÂÂÂif (libxl__stream_write_inuse(stream))
> > > -ÂÂÂÂÂÂÂÂwrite_emulator_xenstore_record(egc, stream);
> > > +ÂÂÂÂif (libxl__stream_write_inuse(stream)) {
> > > +ÂÂÂÂÂÂÂÂif (dss->remus)
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂ/*
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂ* For remus, if libxl__xc_domain_save_done() completes,
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂ* there was an error sending data to the secondary.
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂ* Resume the primary ASAP.
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂ*/
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂstream_complete(egc, stream, 0);
> > 
> > Is there an indication to the caller that things have failed in this
> > way?
> > Would that information be of use to the caller?
> 
> For remus, when we come here, something is wrong regardless of the return
> value.

But does the caller know this? Can it tell.

> 
> > 
> > Or does the called infer this has happened because
> > otherwise libxl_domain_remus_start is not supposed to return?
> 
> Yes, libxl_domain_remus_start() should not return unless somethins is
> wrong.

This really ought to be documented somewhere.



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