Re: [Qemu-devel] [PATCH] Deprecate '-enable-kvm' and '-enable-hax' in favour of '-accel'

[Thomas Huth]

On 02.05.2017 13:59, Daniel P. Berrange wrote:
> On Tue, May 02, 2017 at 01:26:17PM +0200, Thomas Huth wrote:
>> On 02.05.2017 12:48, Christian Borntraeger wrote:
>>> On 05/02/2017 12:37 PM, Thomas Huth wrote:
>>>> On 02.05.2017 12:32, Christian Borntraeger wrote:
>>>>> On 05/02/2017 12:06 PM, Thomas Huth wrote:
>>>>>> The '-enable-...' option do not make too much sense: They do not
>>>>>> allow additional parameters, using '-accel xxx' is shorter than
>>>>>> '-enable-xxx' and we're also inconsistent here, since there is
>>>>>> no '-enable-xen' option available. So let's try to convince the
>>>>>> users to use '-accel xxx' instead.
>>>>>
>>>>> google has 36000 hits for "--enable-kvm" and 18000 hits for "--accel kvm"
>>>>> So I assume this will affect a lot of setups for only a very small 
>>>>> benefit.
>>>>
>>>> I'm aware of the fact that likely a lot of users are still using
>>>> -enable-kvm, and I did not mean that we should remove it soon yet. But
>>>> IMHO we should start now to inform the users that they should slowly
>>>> switch to the better option "-accel" instead, so that we could maybe
>>>> remove this "-enable-xxx" stuff sometime in the distant future (let's
>>>> say QEMU v4.0?).
>>>
>>> I come from the Linux side, where "breaking a working setup" will result in
>>> an angry Linus.
>>
>> IMHO that's a good approach, but I think it should primarily applied for
>> the interfaces that are designed as "API" to other software layers, i.e.
>> things like QMP and the "-machine" parameter.
>> "-enable-kvm" is in my eyes rather a "syntactic sugar" convenience
>> option, so I'd not apply this rule to this option.
>>
>>> We certainly have not such strict rules here and we could
>>> base the decision on the question "how expensive is the maintenance
>>> of this option?". I think marking it as "legacy option" is fine, but I doubt
>>> that removing it will make qemu maintenance cheaper.
>>
>> Likely not. Actually, I have another point of view in mind here: You
>> have to consider that QEMU has a *lot* of options, and I think this is
>> very confusing for the users, especially the new ones. If we always
>> provide two or three ways to achieve a goal, especially in an
>> inconsistent way like we do it here, we likely rather create frustration
>> than joy for the normal users. Providing a clean, straightforward CLI
>> interface one day could help to improve the user experience quite a bit.
> 
> The issue is that we have mutually exclusive requirements here. For a
> straightforward, easy to understand CLI, things like "--enable-kvm" are
> much quicker to discover & understand than "-machine accel=kvm". The
> latter gives much more flexibility since it can set all the other opts,
> but most of those are rarely used by people who are invoking QEMU
> manually/directly. We need the things like -machine for libvirt and
> similar, but they are not end user friendly. Killing all the shortcuts
> like --enable-kvm would cut down the args we expose, but forcing users
> onto more complex syntax for args like -machine is not improving their
> lives in general if they don't need that extra flexibility.

Theoretically yes, but in this case we also have the "-accel kvm" option
which is IMHO also straighforward and easy to understand, and even
shorter than "-enable-kvm". If you look at my patch, I did *not* want to
force the normal users to use "-machine accel=kvm" here, so I don't see
the point of your argument here.

 Thomas