[Libguestfs] [PATCH] New API: mdadm-stop for stopping MD devices.

[Matthew Booth]

On 23/11/11 17:11, Matthew Booth wrote:
> On 23/11/11 16:22, Richard W.M. Jones wrote:
>> On Wed, Nov 23, 2011 at 03:02:19PM +0000, Matthew Booth wrote:
>>> On 23/11/11 14:43, Wanlong Gao wrote:
>>>> This API is used to stop a md device.
>>>> When we want to move a device to another md array, we should
>>>> stop the md device which contained this device first.
>>>
>>> I'm not convinced we should extend the md api in libguestfs to
>>> active manipulation. I wasn't convinced that mdadm-create was
>>> worthwhile either, but it made a test case ever so slightly tidier.
>>> To me, MD devices are the domain of physical machines. We need to be
>>> able to *read* them (for P2V apart from anything else), but I think
>>> manipulation is opening an unnecessary can of worms.
>>
>> But is there any penalty to carrying this?
>
> I can think of 2:
>
> 1. Maintenance: I know you think this is free, but some day mdadm --stop
> might change behaviour, and then the api will break.
>
> 2. A false sense of expectation: Having an incomplete md api can only
> lead to frustration. Implementing a complete md api would require a
> large amount of effort for something which we don't have a convincing
> use case for (i.e. nobody's ever going to use it anyway).

There's another good one, actually: Testing. mdadm-create has already 
created a testing problem, because test-mdadm.sh fails mysteriously on 
my machine, but didn't before and doesn't for you or Wanlong. Especially 
for something like MD, which has a complex subsystem underlying it which 
we don't fully understand in our team, adding and adequately testing a 
new API is an expensive operation.

Matt
-- 
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team

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