Re: [Qemu-devel] [PATCH 2/2] qapi: deprecate implicit filters

[John Snow <jsnow@redhat.com>]

On 8/14/19 6:07 AM, Vladimir Sementsov-Ogievskiy wrote:
> To get rid of implicit filters related workarounds in future let's
> deprecate them now.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  qemu-deprecated.texi      |  7 +++++++
>  qapi/block-core.json      |  6 ++++--
>  include/block/block_int.h | 10 +++++++++-
>  blockdev.c                | 10 ++++++++++
>  4 files changed, 30 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index 2753fafd0b..8222440148 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -183,6 +183,13 @@ the 'wait' field, which is only applicable to sockets in server mode
>  
>  Use blockdev-mirror and blockdev-backup instead.
>  
> +@subsection implicit filters (since 4.2)
> +
> +Mirror and commit jobs inserts filters, which becomes implicit if user
> +omitted filter-node-name parameter. So omitting it is deprecated, set it
> +always. Note, that drive-mirror don't have this parameter, so it will
> +create implicit filter anyway, but drive-mirror is deprecated itself too.
> +
>  @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 4e35526634..0505ac9d8b 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1596,7 +1596,8 @@
>  # @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
> @@ -2249,7 +2250,8 @@
>  # @filter-node-name: the node name that should be assigned to the
>  #                    filter driver that the mirror job inserts into the graph
>  #                    above @device. 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)
>  #
>  # @copy-mode: when to copy data to the destination; defaults to 'background'
>  #             (Since: 3.0)
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 3aa1e832a8..624da0b4a2 100644
> --- a/include/block/block_int.h
> +++ b/include/block/block_int.h
> @@ -762,7 +762,15 @@ struct BlockDriverState {
>      bool sg;        /* if true, the device is a /dev/sg* */
>      bool probed;    /* if true, format was probed rather than specified */
>      bool force_share; /* if true, always allow all shared permissions */
> -    bool implicit;  /* if true, this filter node was automatically inserted */
> +
> +    /*
> +     * @implicit field is deprecated, don't set it to true for new filters.
> +     * If true, this filter node was automatically inserted and user don't
> +     * know about it and unprepared for any effects of it. So, implicit
> +     * filters are workarounded and skipped in many places of the block
> +     * layer code.
> +     */
> +    bool implicit;
>  
>      BlockDriver *drv; /* NULL means no media */
>      void *opaque;
> diff --git a/blockdev.c b/blockdev.c
> index 36e9368e01..b3cfaccce1 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -3292,6 +3292,11 @@ void qmp_block_commit(bool has_job_id, const char *job_id, const char *device,
>      BlockdevOnError on_error = BLOCKDEV_ON_ERROR_REPORT;
>      int job_flags = JOB_DEFAULT;
>  
> +    if (!has_filter_node_name) {
> +        warn_report("Omitting filter-node-name parameter is deprecated, it "
> +                    "will be required in future");
> +    }
> +
>      if (!has_speed) {
>          speed = 0;
>      }
> @@ -3990,6 +3995,11 @@ void qmp_blockdev_mirror(bool has_job_id, const char *job_id,
>      Error *local_err = NULL;
>      int ret;
>  
> +    if (!has_filter_node_name) {
> +        warn_report("Omitting filter-node-name parameter is deprecated, it "
> +                    "will be required in future");
> +    }
> +
>      bs = qmp_get_root_bs(device, errp);
>      if (!bs) {
>          return;
> 

This might be OK to do right away, though.

I asked Markus this not too long ago; do we want to amend the QAPI
schema specification to allow commands to return with "Warning" strings,
or "Deprecated" stings to allow in-band deprecation notices for cases
like these?

example:

{ "return": {},
  "deprecated": True,
  "warning": "Omitting filter-node-name parameter is deprecated, it will
be required in the future"
}

There's no "error" key, so this should be recognized as success by
compatible clients, but they'll definitely see the extra information.

Part of my motivation is to facilitate a more aggressive deprecation of
legacy features by ensuring that we are able to rigorously notify users
through any means that they need to adjust their scripts.

--js