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Re: [Qemu-block] [Qemu-devel] [RFC v4 19/21] blockjobs: Expose manual pr

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [RFC v4 19/21] blockjobs: Expose manual property
Date: Tue, 27 Feb 2018 16:27:37 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

On 02/27/2018 03:57 PM, John Snow wrote:

On 02/27/2018 03:16 PM, Eric Blake wrote:
On 02/23/2018 05:51 PM, John Snow wrote:
Expose the "manual" property via QAPI for the backup-related jobs.
As of this commit, this allows the management API to request the
"concluded" and "dismiss" semantics for backup jobs.

+# @manual: True to use an expanded, more explicit job control flow.
+#          Jobs may transition from a running state to a pending state,
+#          where they must be instructed to complete manually via
+#          block-job-finalize.
+#          Jobs belonging to a transaction must either all or all not
use this
+#          setting. Once a transaction reaches a pending state,
issuing the
+#          finalize command to any one job in the transaction is
+#          to finalize the entire transaction.

The previous commit message talked about mixed-manual transactions, but
this seems to imply it is not possible.  I'm fine if we don't support
mixed-manual transactions, but wonder if it means any changes to the

Otherwise looks reasonable from the UI point of view.

More seriously, this documentation I wrote doesn't address the totality
of the expanded flow. I omitted dismiss here by accident as well. This
is at best a partial definition of the 'manual' property.

I'd like to use _this_ patch to ask the question: "What should the
proper noun for the QEMU 2.12+ Expanded Block Job Management Flow
Mechanism be?"

"Manual" actually doesn't sound too bad; I could also see "Explicit job flow", as in, "within a transaction, all jobs should have the same setting for the choice of Explicit Job Flow" (but then the name 'manual' would have to be changed to match). The idea of a central document, that gets referred to from multiple spots in the QAPI docs, rather than duplicating information throughout the QAPI docs, is reasonable.

I'm not too sure, but "Manual mode" leaves a lot to be desired.

I keep calling it something like "2.12+ Job Management" but that's not
really descriptive.

That, and if someone ever backports the enhanced state machine to a 2.11 branch, it becomes a misnomer.

I conceptualize the feature as the addition of a
purposefully more "needy" and less automatic completion mechanism, hence
the "manual"

Anyway, I'd like to figure out a good "documentation name" for it so I
can point all instances of the creation property (for drive-backup,
drive-mirror, and everyone else) to a central location that explains the
STM and what exactly the differences between manual=on/off are. I'd then
like to expose this property via query and link the documentation there
to this description, too.

"Explicit" and "Manual" are the two best options coming to me as I type this email.

It'd be nice-- under the same arguments that prompted 'dismiss'-- to say
that if a client crashes it can reconnect and discover what kind of
attention certain jobs will need by asking for the manual property back.


Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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