Re: [Qemu-devel] [PATCH v4 08/15] qmp: add block_job_cancel command

[Eric Blake <eblake@redhat.com>]

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On 01/20/2012 01:30 AM, Kevin Wolf wrote:

>>> +++ b/hmp-commands.hx

>> Looking at this from libvirt's perspective, would it be possible to give
>> this a different name?  Then libvirt would know that if
>> block_job_cancel_async exists, we have the official semantics; and if it
>> doesn't exist, then we can try block_job_cancel as a fallback to see if
>> we have the old blocking semantics.
>>
>> But by using the same name as the old unofficial blocking command, it's
>> difficult to tell if we should expect an event, or whether completion of
>> the command means completion of the cancel.
>>

> 
> You're quoting the HMP part, is that intentional? You shouldn't be using
> this at all.

Oh - I missed the .hx file name when trimming my reply.  I agree that
libvirt will be using the QMP, not HMP command.

> 
> Anyway, are there even any qemu versions out there that implement an
> older interface?

The older interface was backported into RHEL 6.2 qemu, so libvirt has to
maintain the distinction (although it can equally be argued that the
distinction only exists in the RHEL build, and therefore, only the RHEL
build of libvirt has to deal with the issues of an early backport of a
qemu feature).

>> Is there any policy on _ vs - in command names?  It seems awkward to
>> have block_job_cancel but query-block-jobs.
> 
> block_job_cancel is HMP, whereas query-block-jobs is a QMP command. QMP
> uses - consistently. Not sure if HMP is consistent, but it tends to use _.

OK, on RHEL 6.2, 'help' on HMP includes help for block_job_cancel, and
'{"execute":"query-commands"}' on QMP includes
{"name":"block_job_cancel"}, with underscores in both locations.  So if
your new QMP command is block-job-cancel, you've met the goal of having
a different spelling from the RHEL backport of the earlier semantics.
And if you stuck with underscores, then it's RHEL's problem to solve :)

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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