Re: [Qemu-devel] [PATCH 2/3] block: Add QMP support for streaming to an intermediate layer

[Alberto Garcia <berto@igalia.com>]

On Thu, Mar 05, 2015 at 03:09:58PM +0100, Kevin Wolf wrote:

> >  { 'command': 'block-stream',
> > -  'data': { 'device': 'str', '*base': 'str', '*backing-file': 'str',
> > -            '*speed': 'int', '*on-error': 'BlockdevOnError' } }
> > +  'data': { 'device': 'str', '*base': 'str', '*top': 'str',
> > +            '*backing-file': 'str', '*speed': 'int',
> > +            '*on-error': 'BlockdevOnError' } }

> A better interface would probably be to allow node names for
> 'device' and leave everything else as it is.

That's possible, but if the API is the same how does libvirt know if
streaming to an intermediate node is possible or not?

> There is no point in specifying some root node as 'device' that
> isn't actually involved in the operation; worse, it isn't even
> possible in the general case because 'top' could have multiple
> users/parents.

The latter is actually a good point, if 'top' is used by 2+ parents
then it makes sense that the ownership of the block job in in 'top',
not in the root node.

I think I will need to investigate the consequences of that.

Berto