Re: [Qemu-devel] [PATCH v3] qapi: add dirty-bitmaps to query-named-block-nodes result

[Markus Armbruster <armbru@redhat.com>]

John Snow <jsnow@redhat.com> writes:

> From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>
> Let's add a possibility to query dirty-bitmaps not only on root nodes.
> It is useful when dealing both with snapshots and incremental backups.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> [Added deprecation information. --js]
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/qapi.c         |  5 +++++
>  qapi/block-core.json |  6 +++++-
>  qemu-deprecated.texi | 12 ++++++++++++
>  3 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/block/qapi.c b/block/qapi.c
> index 917435f022..15f1030264 100644
> --- a/block/qapi.c
> +++ b/block/qapi.c
> @@ -79,6 +79,11 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend *blk,
>          info->backing_file = g_strdup(bs->backing_file);
>      }
>  
> +    if (!QLIST_EMPTY(&bs->dirty_bitmaps)) {
> +        info->has_dirty_bitmaps = true;
> +        info->dirty_bitmaps = bdrv_query_dirty_bitmaps(bs);
> +    }
> +
>      info->detect_zeroes = bs->detect_zeroes;
>  
>      if (blk && blk_get_public(blk)->throttle_group_member.throttle_state) {
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 0d43d4f37c..9210ae233d 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -360,6 +360,9 @@
>  # @write_threshold: configured write threshold for the device.
>  #                   0 if disabled. (Since 2.3)
>  #
> +# @dirty-bitmaps: dirty bitmaps information (only present if node
> +#                 has one or more dirty bitmaps) (Since 4.2)
> +#
>  # Since: 0.14.0
>  #
>  ##
> @@ -378,7 +381,7 @@
>              '*bps_wr_max_length': 'int', '*iops_max_length': 'int',
>              '*iops_rd_max_length': 'int', '*iops_wr_max_length': 'int',
>              '*iops_size': 'int', '*group': 'str', 'cache': 'BlockdevCacheInfo',
> -            'write_threshold': 'int' } }
> +            'write_threshold': 'int', '*dirty-bitmaps': ['BlockDirtyInfo'] } }
>  
>  ##
>  # @BlockDeviceIoStatus:
> @@ -656,6 +659,7 @@
>  #
>  # @dirty-bitmaps: dirty bitmaps information (only present if the
>  #                 driver has one or more dirty bitmaps) (Since 2.0)
> +#                 Deprecated in 4.2; see BlockDirtyInfo instead.
>  #
>  # @io-status: @BlockDeviceIoStatus. Only present if the device
>  #             supports it and the VM is configured to stop on errors
> diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
> index c90b08d553..6374b66546 100644
> --- a/qemu-deprecated.texi
> +++ b/qemu-deprecated.texi
> @@ -134,6 +134,18 @@ The ``status'' field of the ``BlockDirtyInfo'' structure, returned by
>  the query-block command is deprecated. Two new boolean fields,
>  ``recording'' and ``busy'' effectively replace it.
>  
> +@subsection query-block result field dirty-bitmaps (Since 4.2)
> +
> +The ``dirty-bitmaps`` field of the ``BlockInfo`` structure, returned by
> +the query-block command is itself now deprecated. The ``dirty-bitmaps``
> +field of the ``BlockDeviceInfo`` struct should be used instead, which is the
> +type of the ``inserted`` field in query-block replies, as well as the
> +type of array items in query-named-block-nodes.

Would the text be clearer if it talked only about commands, not about
types?

Here's my (laconic) try:

   @subsection query-block result field dirty-bitmaps (Since 4.2)

   In the result of query-block, member ``dirty-bitmaps'' has been moved
   into member ``inserted''.

Aside: same for existing @subsection query-block result field
dirty-bitmaps[i].status (since 4.0).

> +Since the ``dirty-bitmaps`` field is optionally present in both the old and
> +new locations, clients must use introspection to learn where to anticipate
> +the field if/when it does appear in command output.
> +

I find this hint a bit confusing.  Do we need it?

If yes, laconic me again:

   Clients should use introspection to learn whether ``dirty-bitmaps'' is
   in the new location.

>  @subsection query-cpus (since 2.12.0)
>  
>  The ``query-cpus'' command is replaced by the ``query-cpus-fast'' command.