Re: [PATCH v7 2/4] qcow2: add configurations for zoned format extension

[Markus Armbruster <armbru@redhat.com>]

Sam Li <faithilikerun@gmail.com> writes:

> Markus Armbruster <armbru@redhat.com> 于2024年2月19日周一 21:42写道：
>>
>> Sam Li <faithilikerun@gmail.com> writes:
>>
>> > Markus Armbruster <armbru@redhat.com> 于2024年2月19日周一 16:56写道：
>> >>
>> >> Sam Li <faithilikerun@gmail.com> writes:
>> >>
>> >> > Markus Armbruster <armbru@redhat.com> 于2024年2月19日周一 15:40写道：
>> >> >>
>> >> >> Sam Li <faithilikerun@gmail.com> writes:
>> >> >>
>> >> >> > Markus Armbruster <armbru@redhat.com> 于2024年2月19日周一 13:05写道：
>> >> >> >>
>> >> >> >> One more thing...
>> >> >> >>
>> >> >> >> Markus Armbruster <armbru@redhat.com> writes:
>> >> >> >>
>> >> >> >> > I apologize for the delayed review.
>> >> >> >
>> >> >> > No problems. Thanks for reviewing!
>> >> >> >
>> >> >> >> >
>> >> >> >> > Sam Li <faithilikerun@gmail.com> writes:
>> >> >> >> >
>> >> >> >> >> To configure the zoned format feature on the qcow2 driver, it
>> >> >> >> >> requires settings as: the device size, zone model, zone size,
>> >> >> >> >> zone capacity, number of conventional zones, limits on zone
>> >> >> >> >> resources (max append bytes, max open zones, and max_active_zones).
>> >> >> >> >>
>> >> >> >> >> To create a qcow2 image with zoned format feature, use command like
>> >> >> >> >> this:
>> >> >> >> >> qemu-img create -f qcow2 zbc.qcow2 -o size=768M \
>> >> >> >> >> -o zone.size=64M -o zone.capacity=64M -o zone.conventional_zones=0 \
>> >> >> >> >> -o zone.max_append_bytes=4096 -o zone.max_open_zones=6 \
>> >> >> >> >> -o zone.max_active_zones=8 -o zone.mode=host-managed
>> >> >> >> >>
>> >> >> >> >> Signed-off-by: Sam Li <faithilikerun@gmail.com>
>> >> >> >> >
>> >> >> >> > [...]
>> >> >> >> >
>> >> >> >> >> diff --git a/qapi/block-core.json b/qapi/block-core.json
>> >> >> >> >> index ca390c5700..e2e0ec21a5 100644
>> >> >> >> >> --- a/qapi/block-core.json
>> >> >> >> >> +++ b/qapi/block-core.json
>> >> >> >> >> @@ -5038,6 +5038,67 @@
>> >> >> >> >>  { 'enum': 'Qcow2CompressionType',
>> >> >> >> >>    'data': [ 'zlib', { 'name': 'zstd', 'if': 'CONFIG_ZSTD' } ] }
>> >> >> >> >>
>> >> >> >> >> +##
>> >> >> >> >> +# @Qcow2ZoneModel:
>> >> >> >> >> +#
>> >> >> >> >> +# Zoned device model used in qcow2 image file
>> >> >> >> >> +#
>> >> >> >> >> +# @host-managed: The host-managed model only allows sequential write over the
>> >> >> >> >> +#     device zones.
>> >> >> >> >> +#
>> >> >> >> >> +# Since 8.2
>> >> >> >> >> +##
>> >> >> >> >> +{ 'enum': 'Qcow2ZoneModel',
>> >> >> >> >> +  'data': [ 'host-managed'] }
>> >> >> >> >> +
>> >> >> >> >> +##
>> >> >> >> >> +# @Qcow2ZoneHostManaged:
>> >> >> >> >> +#
>> >> >> >> >> +# The host-managed zone model.  It only allows sequential writes.
>> >> >> >> >> +#
>> >> >> >> >> +# @size: Total number of bytes within zones.
>> >> >> >> >
>> >> >> >> > Default?
>> >> >> >
>> >> >> > It should be set by users. No default value provided. If it's unset
>> >> >> > then it is zero and an error will be returned.
>> >> >>
>> >> >> If the user must provide @size, why is it optional then?
>> >> >
>> >> > It is not optional when the zone model is host-managed. If it's
>> >> > non-zoned, then we don't care about zone info. I am not sure how to
>> >> > make it unoptional.
>> >>
>> >> We have:
>> >>
>> >>    blockdev-create argument @options of type BlockdevCreateOptions
>> >>
>> >>    BlockdevCreateOptions union branch @qcow2 of type
>> >>    BlockdevCreateOptionsQcow2, union tag member is @driver
>> >>
>> >>    BlockdevCreateOptionsQcow2 optional member @zone of type
>> >>    Qcow2ZoneCreateOptions, default not zoned
>> >>
>> >>    Qcow2ZoneCreateOptions union branch @host-managed of type
>> >>    Qcow2ZoneHostManaged, union tag member is @mode
>> >>
>> >>    Qcow2ZoneHostManaged optional member @size of type size.
>> >>
>> >> Making this member @size mandatory means we must specify it when
>> >> BlockdevCreateOptionsQcow2 member @zone is present and @zone's member
>> >> @mode is "host-managed".  Feels right to me.  Am I missing anything?
>> >
>> > That's right. And the checks when creating such an img can help do
>> > that. It's not specified in the .json file directly.
>>
>> What would break if we did specify it in the QAPI schema directly?
>
> Nothing I think. We can keep the current schema and add a default zone
> size like 131072.

I believe making the member mandatory makes a lot more sense.

I guess we can keep @capacity and @max-append-bytes keep optional *if*
we can come up with sensible defaults.

>> [...]