Re: [Qemu-block] [Qemu-devel] [RFC v4 07/21] blockjobs: add block_job_verb permission table

[Eric Blake]

On 02/23/2018 05:51 PM, John Snow wrote:
> Which commands ("verbs") are appropriate for jobs in which state is
> also somewhat burdensome to keep track of.
>
> As of this commit, it looks rather useless, but begins to look more
> interesting the more states we add to the STM table.
>
> A recurring theme is that no verb will apply to an 'undefined' job.

Back to the argument of whether we even want that state.

> =======
> Changes
> =======
>
> (1)
>
> To facilitate "nice" error checking, all five major block-job verb
> interfaces in blockjob.c now support an errp parameter:
>
> - block_job_user_cancel is added as a new interface.
> - block_job_user_pause gains an errp paramter
> - block_job_user_resume gains an errp parameter
> - block_job_set_speed already had an errp parameter.
> - block_job_complete already had an errp parameter.
>
> (2)
>
> block-job-pause and block-job-resume will no longer no-op when trying
> to pause an already paused job, or trying to resume a job that isn't
> paused. These functions will now report that they did not perform the
> action requested because it was not possible.
>
> iotests have been adjusted to address this new behavior.

Seems reasonable.  Hopefully shouldn't trip up libvirt too badly (if 
libvirt attempted a redundant job transition that used to silently 
succeed and now fails, the failure message should be pretty obvious that 
it was a no-op attempt).

> (3)
>
> block-job-complete doesn't worry about checking !block_job_started,
> because the permission table guards against this.
>
> (4)
>
> test-bdrv-drain's job implementation needs to announce that it is
> 'ready' now, in order to be completed.
>
> Signed-off-by: John Snow <address@hidden>
> ---

Reviewed-by: Eric Blake <address@hidden>

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