Re: [Qemu-devel] [PATCH 1/3] block: Support streaming to an intermediate layer

[Kevin Wolf]

Am 05.03.2015 um 15:58 hat Alberto Garcia geschrieben:
> On Thu, Mar 05, 2015 at 03:04:25PM +0100, Kevin Wolf wrote:
> 
> > The bs parameter is now only used for the following things:
> > 
> > 1. As the default for top
> 
> Right.
> 
> > 2. For error handling: Any errors are reported for bs, even though
> >    they are actually for top. Is this correct behaviour? It looks
> >    questionable to me.
> 
> Hmm... I guess you mean when calling block_job_error_action(), I
> probably overlooked that.

Yes, that and the check whether iostatus is enabled.

> > 3. As the BDS that owns the job
> > 
> > My question is whether we can't simply call stream_start() with an
> > intermediate node as bs instead of introducing a new parameter. I'm
> > not completely sure about the consequences of 3., i.e. moving
> > ownership of a block job to some BDS somewhere down the chain, but
> > otherwise it should be possible and seems cleaner.
> 
> We can, that was actually the first thing I tried and it does work,
> but then I noticed that other parts of the code would need changes,
> e.g. qmp_query_block_jobs() must be modified to iterate over all nodes
> of each device.
> 
> Since I was also not sure about the consequences of such a change I
> opted for the conservative approach.

I see. I'm worried about the external API. If we let the root node own
the job, we may paint ourselves into a corner with respect to nodes with
multiple users and therefore multiple possible root nodes.

Kevin