Re: [PATCH v2 2/2] qapi: deprecate implicit filters

[Peter Krempa <pkrempa@redhat.com>]

On Fri, Nov 08, 2019 at 13:16:55 +0300, Vladimir Sementsov-Ogievskiy wrote:
> To get rid of implicit filters related workarounds in future let's
> deprecate them now.
> 
> Deprecation warning breaks some bash iotests output, so fix it here
> too: in most of cases just add filter-node-name in test.
> 
> In 161 add FIXME and deprecation warning into 161.out.
> 
> In 249, the test case is changed, as we don't need to test "default"
> filter node name anymore.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  qemu-deprecated.texi       |  6 ++++++
>  qapi/block-core.json       |  9 ++++++---
>  include/block/block_int.h  | 10 +++++++++-
>  blockdev.c                 | 10 ++++++++++
>  tests/qemu-iotests/094     |  1 +
>  tests/qemu-iotests/095     |  6 ++++--
>  tests/qemu-iotests/109     |  1 +
>  tests/qemu-iotests/127     |  1 +
>  tests/qemu-iotests/141     |  5 ++++-
>  tests/qemu-iotests/144     |  3 ++-
>  tests/qemu-iotests/156     |  1 +
>  tests/qemu-iotests/161     |  7 +++++++
>  tests/qemu-iotests/161.out |  1 +
>  tests/qemu-iotests/185     |  3 +++
>  tests/qemu-iotests/191     |  2 ++
>  tests/qemu-iotests/229     |  1 +
>  tests/qemu-iotests/247     |  8 +++++---
>  tests/qemu-iotests/249     |  5 +++--
>  tests/qemu-iotests/249.out |  2 +-
>  19 files changed, 68 insertions(+), 14 deletions(-)
> 
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index 296bfc93a3..c969faf55a 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -204,6 +204,12 @@ and accurate ``query-qmp-schema'' command.
>  Character devices creating sockets in client mode should not specify
>  the 'wait' field, which is only applicable to sockets in server mode
>  
> +@subsection implicit filters in mirror and commit (since 4.2)
> +
> +Mirror and commit jobs insert filters, which becomes implicit if user
> +omitted @option(filter-node-name) parameter. So omitting it is deprecated
> +in ``blockdev-mirror'', ``drive-mirror'' and ``block-commit'', set it always.
> +
>  @section Human Monitor Protocol (HMP) commands
>  
>  @subsection The hub_id parameter of 'hostfwd_add' / 'hostfwd_remove' (since 3.1)
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 93530d3a13..37caed775f 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1659,7 +1659,8 @@
>  # @filter-node-name: the node name that should be assigned to the
>  #                    filter driver that the commit job inserts into the graph
>  #                    above @top. If this option is not given, a node name is
> -#                    autogenerated. (Since: 2.9)
> +#                    autogenerated. Omitting this option is deprecated, it will
> +#                    be required in future. (Since: 2.9)
>  #
>  # @auto-finalize: When false, this job will wait in a PENDING state after it has
>  #                 finished its work, waiting for @block-job-finalize before

Note that 'block-commit' and 'drive-mirror' commands are used by libvirt
in the pre-blockdev era. In those instances we gather statistics of
block devices by nesting in the output of query-blockstats and
query-block rather than selecting the appropriate info by any other
means (e.g. by node name).

This means that the output MUST stay consistend when block jobs are used
and the hack this patch is deprcating will break those.

Note that in libvirt we don't plan to invest time to add workarounds for
non-blockdev cases since blockdev by itself is complex enough and I'd
strongly prefer not having a third code path to care about.

Given that -blockdev can't be used in all cases (e.g. for sd-cards)
which also blocks deprecation of -drive I don't think that hiding of
implicit filter nodes can be deprecated until -drive is deprecated.