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

[Eric Blake <eblake@redhat.com>]

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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.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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