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Re: [PATCH 0/9] mirror: allow switching from background to active mode

From: Fiona Ebner
Subject: Re: [PATCH 0/9] mirror: allow switching from background to active mode
Date: Wed, 1 Mar 2023 15:49:17 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0

Am 01.03.23 um 15:34 schrieb Vladimir Sementsov-Ogievskiy:
> On 24.02.23 17:48, Fiona Ebner wrote:
>> With active mode, the guest write speed is limited by the synchronous
>> writes to the mirror target. For this reason, management applications
>> might want to start out in background mode and only switch to active
>> mode later, when certain conditions are met. This series adds a
>> block-job-change QMP command to acheive that, as well as
>> job-type-specific information when querying block jobs, which
>> can be used to decide when the switch should happen.
>> For now, only the direction background -> active is supported.
>> The information added upon querying is whether the target is actively
>> synced, the total data sent, and the remaining dirty bytes.
>> Initially, I tried to go for a more general 'job-change' command, but
>> I couldn't figure out a way to avoid mutual inclusion between
>> block-core.json and job.json.
> Hmm, what do you mean? As I understand job-* API is "new" and
> block-job-* is "old", so we'd better add job-change command

My issue is that when I go for that with a JobChangeOptions union in
job.json and declare JobChangeOptionsMirror in block-core.json (it needs
to know about MirrorCopyMode and all other mirror-related declarations
are there so it's the natural place), then I need to include
block-core.json in job.json so that the JobChangeOptions union can
reference JobChangeOptionsMirror. But that is a mutual inclusion.

I guess it would be possible to move MirrorCopyMode to job.json and
declare JobChangeOptionsMirror in job.json, but that didn't feel right
and would mean moving more and more to job.json whenever extending
job-change requires it.

But maybe I'm missing something obvious? Haven't worked much with the
QAPI yet.

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