On Fri, Aug 10, 2018 at 18:26:57 +0200, Kevin Wolf wrote:
> The block-commit QMP command required specifying the top and base nodes
> of the commit jobs using the file name of that node. While this works
> in simple cases (local files with absolute paths), the file names
> generated for more complicated setups can be hard to predict.
> 
> This adds two new options top-node and base-node to the command, which
> allow specifying node names instead. They are mutually exclusive with
> the old options.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qapi/block-core.json | 24 ++++++++++++++++++------
>  blockdev.c           | 32 ++++++++++++++++++++++++++++++--
>  2 files changed, 48 insertions(+), 8 deletions(-)

While the below is not strictly relevant to this patch usage
block-commit is not possible when using -blockdev. Thus the new
arguments are not very useful otherwise.

With the new options I'm getting:

{"execute":"block-commit",
 "arguments": { "device":"libvirt-3-format",
                "job-id":"libvirt-3-format",
                "top-node":"libvirt-8-format",
                "base-node":"libvirt-9-format",
                "auto-finalize":true,
                "auto-dismiss":false},
 "id":"libvirt-16"}

{"id":"libvirt-16",
 "error":{"class":"GenericError",
          "desc":"Block node is read-only"}}

I'm pointing into the backing chain so the files are declared as read-only.

It works just-fine if I open them as read-write with
-blockdev/blockdev-add but that obviously is not correct as you can't
then share parts of the backing chain with other VMs due to image
locking.

libvirt-3-format is read-write and all other node names are readonly in
the above example.

The same also happens when using filenames:

{"execute":"block-commit",
 "arguments" : {"device":"libvirt-3-format",
                "job-id":"libvirt-3-format",
                "top":"/var/lib/libvirt/images/rhel7.3.1483615252",
                "base":"/var/lib/libvirt/images/rhel7.3.1483605924",
                "auto-finalize":true,
                "auto-dismiss":false},
 "id":"libvirt-13"}

{"id":"libvirt-13","error":{"class":"GenericError","desc":"Block node is read-only"}}


When I use the drive alias rather than the node-name for the 'device'
argument it works as expected.

{"execute":"block-commit",
 "arguments": { "device":"drive-virtio-disk0",
                "job-id":"drive-virtio-disk0",
                "top":"/var/lib/libvirt/images/rhel7.3.1483536402",
                "base":"/var/lib/libvirt/images/rhel7.3.1483545313"},
 "id":"libvirt-18"}


I was not able to find anything which would allow to reopen the file R/W
in case of the block-commit operation, but I suspect it should be done
automatically as previously it was done that way prior to -blockdev.

Peter