Re: [Qemu-devel] [PATCH v3 0/7] block: Handle null backing link

[Eric Blake <eblake@redhat.com>]

On 02/24/2018 09:40 AM, Max Reitz wrote:
> Currently, we try to rewrite every occurrence of "backing": null into
> "backing": "" in qmp_blockdev_add().  However, that breaks using the
> same "backing": null construction in json:{} file names (which do not go
> through qmp_blockdev_add()).  Currently, these then just behave as if
> the option has not been specified.
> 
> Since there is actually only one place where we evaluate the @backing
> option to find out whether not to use a backing file, we can instead
> just check for null there.  It doesn't matter that this changes the
> runtime state of the option from "" to null, because nobody really does
> anything with that runtime state anyway (except put it into qemu again,
> but qemu doesn't care whether it's "" or null).
> 
> And in the future, it's much better if we get it to be null in that
> runtime state sooner than later -- see patch 7.
> 
> 
> Note that it was Markus (who's away having a good time, I hope) who
> proposed qobject_to(), so I guess he won't object too much to seeing the
> concept having landed in his tree once he returns.
> (Although he hasn't reviewed the previous iteration of this series,
>   which included it already.)
> 
> 
> v3:
> - Added patch 1 so we can use a common macro in patch 2 (instead of
>    invoking _Static_assert() directly), but still keep the explanatory
>    message
> 

This series mostly touches QAPI, so I'm probably going to include it in 
my pending qapi pull request in time for soft freeze.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org