Re: [Qemu-devel] [PATCH v12 10/19] block: Add QMP support for streaming to an intermediate layer

[Kevin Wolf <kwolf@redhat.com>]

Am 26.10.2016 um 19:23 hat Alberto Garcia geschrieben:
> On Wed 26 Oct 2016 04:58:00 PM CEST, Kevin Wolf <kwolf@redhat.com> wrote:
> > Am 26.10.2016 um 12:29 hat Alberto Garcia geschrieben:
> >> This patch makes the 'device' parameter of the 'block-stream' command
> >> accept a node name that is not a root node.
> >> 
> >> In addition to that, operation blockers will be checked in all
> >> intermediate nodes between the top and the base node.
> >> 
> >> Signed-off-by: Alberto Garcia <berto@igalia.com>
> >
> >> --- a/qapi/block-core.json
> >> +++ b/qapi/block-core.json
> >> @@ -1464,6 +1464,10 @@
> >>  # with query-block-jobs.  The operation can be stopped before it has completed
> >>  # using the block-job-cancel command.
> >>  #
> >> +# The node that receives the data is called the top image, can be located in
> >> +# any part of the chain (but always above the base image; see below) and can be
> >> +# specified using its device or node name.
> >> +#
> >>  # If a base file is specified then sectors are not copied from that base file and
> >>  # its backing chain.  When streaming completes the image file will have the base
> >>  # file as its backing file.  This can be used to stream a subset of the backing
> >> @@ -1475,12 +1479,12 @@
> >>  # @job-id: #optional identifier for the newly-created block job. If
> >>  #          omitted, the device name will be used. (Since 2.7)
> >>  #
> >> -# @device: the device name or node-name of a root node
> >> +# @device: the device or node name of the top image
> >>  #
> >>  # @base:   #optional the common backing file name
> >>  #
> >> -# @backing-file: #optional The backing file string to write into the active
> >> -#                          layer. This filename is not validated.
> >> +# @backing-file: #optional The backing file string to write into the top
> >> +#                          image. This filename is not validated.
> >>  #
> >>  #                          If a pathname string is such that it cannot be
> >>  #                          resolved by QEMU, that means that subsequent QMP or
> >
> > As we discussed in v10, this is not discoverable through
> > introspection.  You added patch 18 which introduces a base-node option
> > and can serve as a witness for the changed semantics, which is
> > good. Should this be documented here?
> 
> In the commit message I don't see why not, but in the JSON file?
> 
> "This feature was added together with the base-node parameter" ?

Eric may have a better suggestion for the wording, but maybe something
like this:

"Presence of this feature can't directly be tested with introspection;
check for the presence of base-node instead as a witness for it."

Kevin