Re: [Qemu-block] [Qemu-devel] [PATCH v1 3/6] qemu-img: add support for -n arg to dd command

[Max Reitz]

On 30.01.2017 19:37, Eric Blake wrote:
> On 01/26/2017 07:27 AM, Daniel P. Berrange wrote:
>> On Thu, Jan 26, 2017 at 08:35:30PM +0800, Fam Zheng wrote:
>>> On Thu, 01/26 11:04, Daniel P. Berrange wrote:
>>>> The -n arg to the convert command allows use of a pre-existing image,
>>>> rather than creating a new image. This adds a -n arg to the dd command
>>>> to get feature parity.
>>>
>>> I remember there was a discussion about changing qemu-img dd's default to a
>>> "conv=nocreat" semantic, if so, "-n" might not be that useful. But that part
>>> hasn't made it into the tree, and I'm not sure which direction we should 
>>> take.
>>> (Personally I think default to nocreat is a good idea).
>>
>> Use nocreat by default would be semantically different from real "dd"
>> binary which feels undesirable if the goal is to make "qemu-img dd"
>> be as consistent with "dd" as possible.
>>
>> It would be trivial to rewrite this patch to add support for the "conv"
>> option, allowing the user to explicitly give 'qemu-img dd conv=nocreat'
>> instead of my 'qemu-img dd -n' syntax, without changing default semantics.
> 
> Adding 'conv=nocreat' (and not '-n') feels like the right way to me.

The original idea was to make conv=nocreat a mandatory option, I think.
qemu-img was supposed error out if the user did not specify it.

Max

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