Re: [Qemu-devel] [PATCH v2 1/1] qmp: marking qmp_cpu as deprecated

[Eric Blake <eblake@redhat.com>]

On 12/19/2017 06:19 AM, Daniel Henrique Barboza wrote:

>> Let's compare behavior:
>>
>> 0. Status quo                       do nothing and succeed
>> 1. Your patch                       fail with GenericError
>> 2. Your patch less error_setg()     do nothing and succeed
>> 3. Immediate removal                fail with CommandNotFound
>>
>> Does the difference between 1. and 3. matter at all?  Or is it just
>> deprecation cargo cult?
> 
> Good point. If both the deprecation message and the removal will
> result in error for the user ....
> 
>>
>> Here's my take on it.  I'd prefer 3. Immediate removal.  I'd also be
>> fine with 2. Your patch less error_setg(), followed by removal after the
>> customary deprecation period.  1. plus later removal just doesn't make
>> sense to me, but it's really no big deal, so if you guys want it...
> 
> It all goes down to whether we consider qmp_cpu, a QMP command that does
> nothing since its creation and apparently no one ever used it, a 
> feature. If it's a
> feature, then I vote for (2) and removal after 2 releases following the 
> regular
> deprecation policy.
> 
> If we consider that applying the policy to qmp_cpu is more trouble than 
> it's worth,
> I'll gladly resend this patch removing it entirely and rewording the 
> qemu-doc.texi
> entry to mention that it was removed because it did nothing and it was of
> no use for anyone.
> 

My vote: (3).  No one was using qmp_cpu for anything, while deprecation 
exists to allow a user a chance to fix their workflow to adjust from one 
thing that works (but badly) to its replacement that also works (and 
will be supported long term).  Since our replacement is nothing, we are 
admitting that no one was relying on the command, and I don't see the 
point in a deprecation delay. Just nuke it!

qemu-doc.texi doesn't even need to mention the command; the commit 
message is enough to document our reasons for complete removal.

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