Re: [RFC 1/4] drive-mirror: add support for sync=bitmap mode=never

[Markus Armbruster <armbru@redhat.com>]

Fiona Ebner <f.ebner@proxmox.com> writes:

> From: John Snow <jsnow@redhat.com>
>
> This patch adds support for the "BITMAP" sync mode to drive-mirror and
> blockdev-mirror. It adds support only for the BitmapSyncMode "never,"
> because it's the simplest mode.
>
> This mode simply uses a user-provided bitmap as an initial copy
> manifest, and then does not clear any bits in the bitmap at the
> conclusion of the operation.
>
> Any new writes dirtied during the operation are copied out, in contrast
> to backup. Note that whether these writes are reflected in the bitmap
> at the conclusion of the operation depends on whether that bitmap is
> actually recording!
>
> This patch was originally based on one by Ma Haocong, but it has since
> been modified pretty heavily.
>
> Suggested-by: Ma Haocong <mahaocong@didichuxing.com>
> Signed-off-by: Ma Haocong <mahaocong@didichuxing.com>
> Signed-off-by: John Snow <jsnow@redhat.com>
> [FG: switch to bdrv_dirty_bitmap_merge_internal]
> Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
> Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
> [FE: rebase for 9.0
>      update version and formatting in QAPI]
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

[...]

> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index ab5a93a966..ac05483958 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2181,6 +2181,15 @@
>  #     destination (all the disk, only the sectors allocated in the
>  #     topmost image, or only new I/O).
>  #
> +# @bitmap: The name of a bitmap to use for sync=bitmap mode.  This
> +#     argument must be present for bitmap mode and absent otherwise.
> +#     The bitmap's granularity is used instead of @granularity.
> +#     (Since 9.0).

What happens when the user specifies @granularity anyway?  Error or
silently ignored?

> +#
> +# @bitmap-mode: Specifies the type of data the bitmap should contain
> +#     after the operation concludes.  Must be present if sync is
> +#     "bitmap".  Must NOT be present otherwise.  (Since 9.0)

Members that must be present when and only when some enum member has a
certain value should perhaps be in a union branch.  Perhaps the block
maintainers have an opinion here.

> +#
>  # @granularity: granularity of the dirty bitmap, default is 64K if the
>  #     image format doesn't have clusters, 4K if the clusters are
>  #     smaller than that, else the cluster size.  Must be a power of 2
> @@ -2223,7 +2232,9 @@
>  { 'struct': 'DriveMirror',
>    'data': { '*job-id': 'str', 'device': 'str', 'target': 'str',
>              '*format': 'str', '*node-name': 'str', '*replaces': 'str',
> -            'sync': 'MirrorSyncMode', '*mode': 'NewImageMode',
> +            'sync': 'MirrorSyncMode', '*bitmap': 'str',
> +            '*bitmap-mode': 'BitmapSyncMode',
> +            '*mode': 'NewImageMode',
>              '*speed': 'int', '*granularity': 'uint32',
>              '*buf-size': 'int', '*on-source-error': 'BlockdevOnError',
>              '*on-target-error': 'BlockdevOnError',
> @@ -2507,6 +2518,15 @@
>  #     destination (all the disk, only the sectors allocated in the
>  #     topmost image, or only new I/O).
>  #
> +# @bitmap: The name of a bitmap to use for sync=bitmap mode.  This
> +#     argument must be present for bitmap mode and absent otherwise.
> +#     The bitmap's granularity is used instead of @granularity.
> +#     (Since 9.0).
> +#
> +# @bitmap-mode: Specifies the type of data the bitmap should contain
> +#     after the operation concludes.  Must be present if sync is
> +#     "bitmap".  Must NOT be present otherwise.  (Since 9.0)
> +#
>  # @granularity: granularity of the dirty bitmap, default is 64K if the
>  #     image format doesn't have clusters, 4K if the clusters are
>  #     smaller than that, else the cluster size.  Must be a power of 2
> @@ -2557,7 +2577,8 @@
>  { 'command': 'blockdev-mirror',
>    'data': { '*job-id': 'str', 'device': 'str', 'target': 'str',
>              '*replaces': 'str',
> -            'sync': 'MirrorSyncMode',
> +            'sync': 'MirrorSyncMode', '*bitmap': 'str',
> +            '*bitmap-mode': 'BitmapSyncMode',
>              '*speed': 'int', '*granularity': 'uint32',
>              '*buf-size': 'int', '*on-source-error': 'BlockdevOnError',
>              '*on-target-error': 'BlockdevOnError',

[...]