Re: [Qemu-devel] [PATCH v7 2/6] qmp: Create IOThrottle structure

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> On 08/16/2017 11:13 AM, Markus Armbruster wrote:
>> Markus Armbruster <armbru@redhat.com> writes:
>> 
>
>>>
>>> Conclusion: no consensus, yet.
>> 
>> All right, let's start over and try to resolve the impasse and/or
>> misunderstanding.
>> 
>> Type BlockIOThrottle lives in qapi/block-core.json, and is used by QMP
>> command block_set_io_throttle.  Since 1.1.
>> 
>> Pradeep has a use case for throttling in fsdev.  Instead of duplicating
>> the relevant parts of BlockIOThrottle, qmp_block_set_io_throttle() and
>> hmp_block_set_io_throttle(), he factors them out smartly, into
>> 
>> * [PATCH 2] IOThrottle, base type of BlockIOThrottle
>> 
>> * [PATCH 3] throttle_set_io_limits(), called by
>>   qmp_block_set_io_throttle()
>> 
>> * [PATCH 4] hmp_initialize_io_throttle(), called by
>>   hmp_block_set_io_throttle()
>> 
>> throttle_set_io_limits() goes into existing util/throttle.c, and
>> hmp_initialize_io_throttle() goes into existing hmp.c.  The question is
>> where IOThrottle should go.
>
> Good summary.
>
>> 
>> Pradeep proposes to put it in new qapi/throttle.json.  Certainly
>> defensible, but I really don't like putting every little thing shared
>> across subsystem boundaries into its own schema file.
>
> I agree with the dislike of creating new files, if an existing file is
> adequate.
>
>> 
>> Let me step back and discuss why we split the QAPI schema into multiple
>> files in the first place.  For me, the one and only reason is
>> MAINTAINERS.
>
> Indeed, that's a good description of why splits would be appropriate.
> So the obvious next question is if this is a case that needs a new
> maintainer.
>
>> 
>> If the block folks should continue to maintain IOThrottle, then it
>> should stay put in block-core.json.
>
> I think Manos' work on making throttling a filter driver at the block
> layer is proof enough that it it is still fine to keep throttling
> maintained in block-core.json.
>
>> 
>> If somebody else should start maintaining it, it should move.  We'd need
>> a suitable entry in MAINTAINERS then.
>> 
>> I don't see why maintenance should change, and therefore believe it
>> should stay put.
>> 
>> Eric?
>
> I think we're in violent agreement: don't create a new file, and having
> the new factored type live in block-core.json is the best fit because we
> haven't come up with any reasons why it needs to be split.

Thanks, Eric.

Pradeep, please put IOThrottle right before BlocIOThrottle in
block-core.json.  Use it in fsdev.json without including
block-core.json.  Sorry for the delay.