Re: [Qemu-devel] [PATCH v4 1/2] qemu.py: make 'args' public

[Cleber Rosa]

On 07/26/2017 01:35 PM, Stefan Hajnoczi wrote:
> On Tue, Jul 25, 2017 at 11:30:16AM -0400, Cleber Rosa wrote:
>> On 07/25/2017 09:37 AM, Stefan Hajnoczi wrote:
>>> On Mon, Jul 24, 2017 at 02:44:37PM +0200, Amador Pahim wrote:
>>>> Signed-off-by: Amador Pahim <address@hidden>
>>>> Reviewed-by: Fam Zheng <address@hidden>
>>>> ---
>>>>  scripts/qemu.py               | 10 +++++-----
>>>>  tests/qemu-iotests/iotests.py | 18 +++++++++---------
>>>>  2 files changed, 14 insertions(+), 14 deletions(-)
>>>
>>> Please don't do this, it encourages code duplication.  Now arbitrary
>>> users can start accessing the public field directly instead of adding a
>>> reusable interfaces like add_monitor_telnet(), add_fd(), etc.
>>>
>>
>> Judging from tests/qemu-iotests/iotests.py:VM and your comment above, I
>> assume you see value in simple wrappers such as:
>>
>>    def add_device(self, opts):
>>         self._args.append('-device')
>>         self._args.append(opts)
>>         return self
>>
>> I honestly do not see any value here.  I do see value in other wrappers,
>> such as add_drive(), in which default values are there for convenience,
>> and a drive count is kept.  In the end, my point is that the there are
>> cases when a wrapper is just an annoyance and provides nothing more than
>>  the illusion of a better design.
> 
> I don't see much value in simple wrappers either besides method chaining
> (more on that below).
> 
> Getting back to this patch, I can only review patches in the context of
> the current code base.  I don't know future plans you may have.  The
> change may make sense together with other new changes that use a public
> args field in a useful way - it just doesn't make sense the way it has
> been presented in isolation.
> 

I think I described what the intention is: support tests that use
instances directly.  But yes, I think it can be better backed by real
code making use of it.

> About method chaining, the current code seems to be written with method
> chaining in mind:
> 
> https://en.wikipedia.org/wiki/Method_chaining#Python
> 
> If all arguments are methods then everything can be chained:
> 
>   (vm.add_fd(fd.fileno(), 1, 'image0')
>      .add_drive('fd:image0', interface='none')
>      .add_device('virtio-blk-pci,drive=drive0'))
> 
> So I guess there is a small value in having add_device().  That said,
> tests don't take advantage of method chaining much.
> 

Right, just about the same amount of value of a more generic
"add_arg(option, arguments=[])".  IMO not even worth its maintenance costs.

-- 
Cleber Rosa
[ Sr Software Engineer - Virtualization Team - Red Hat ]
[ Avocado Test Framework - avocado-framework.github.io ]
[  7ABB 96EB 8B46 B94D 5E0F  E9BB 657E 8D33 A5F2 09F3  ]

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