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Re: [Qemu-block] [Qemu-devel] [PATCH v10 00/14] block: incremental backu

From: John Snow
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH v10 00/14] block: incremental backup transactions using BlockJobTxn
Date: Tue, 3 Nov 2015 17:07:25 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

On 11/03/2015 12:46 PM, John Snow wrote:
> On 11/03/2015 10:22 AM, Stefan Hajnoczi wrote:
>> On Fri, Oct 23, 2015 at 07:56:38PM -0400, John Snow wrote:
>>> Welcome to V10!
>>> Where'd 8 and 9 go? Private off-list missives from Fam.
>>> Now you, I, and everyone on qemu-devel are staring at V10.
>>> What's new in V10?
>>> I replaced the per-action "transactional-cancel" parameter with
>>> a per-transaction paremeter named "err-cancel" which is implemented
>>> as an enum in case we want to add new behaviors in the future, such
>>> as a "jobs only" cancel mode.
>>> For now, it's "all" or "none", and if you use it with actions that
>>> do not support the latent transactional cancel, you will receive
>>> an error for your troubles.
>> I left comments on a few patches.
>> The "err-cancel" and "ActionCancelMode" naming does not describe the
>> concept fully, since successful block jobs will also behave differently
>> (waiting for each other to finish before fully completing).
>> "blockjob-transactions" is the best name I can think of that describes
>> the full concept rather than focus on just cancellation.
> There's two hard problems in Computer Science...
> I mean, cancellation certainly is the biggest change in net behavior,
> though we are fiddling with the timings of the completion notices.
> OK, so continuing on my inability to name this feature ...
> blockjob-transactions = { individual, grouped, jobs-only }
> where we'd support "individual" as the default,
> "grouped" is the forced cancellation mode, and
> jobs-only is a hypothetical future mode that adds jobs to the group, and
> ignoring non-jobs' inability to join the transaction.
> Still, it seems weird to have:
> transaction 'properties': {'blockjob-transactions': 'grouped'},
> it feels redundant to me.
> How about:
> completion-mode = { individual, grouped }
> Avoids repeating "Transaction" and does not hyperfocus on cancellation.

Version "10.5" is on https://github.com/jnsnow/qemu.git

- Rebased on master to play nice with the new QAPI checkins (#3, #12)
- Fixed error path leak (#3)
- Renamed the Transaction Property and enum values (#12, #13) as above
  ("completion-mode", "individual", "grouped")
- Fixed a leak in the block_job_txn qtest (#14)

If the names and QMP interface look good I'll publish as v11.


>> Besides that I'm happy with the QMP interface.

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