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Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sec
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present |
Date: |
Wed, 30 Sep 2015 18:06:33 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 |
On 30/09/2015 18:02, Jeff Cody wrote:
> As a general rule for blockjobs, I disagree.
>
> Right away, there is a key difference: we don't know that the image is
> (or should be) empty.
Not necessarily empty. sync='top' && mode='existing' &&
!target->backing_file, for example, makes sense if the target is a copy
of source->bs.
In fact, commit of the active layer is almost exactly a mode='existing'
drive-mirror operation.
But if you use mode == 'existing', and don't provide an image that
follows the rules, it's garbage-in garbage-out. The sequence of
operation makes sense, but the resulting image does not.
Paolo
> With mode != "existing", we know the image
> should be empty, since we just created it (although for a host device,
> it may have extraneous data in it). So I think it is not so much what
> we can assume about an existing image, as it is what we cannot assume.
> And that could potentially influence some block jobs.
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Kevin Wolf, 2015/10/01
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Paolo Bonzini, 2015/10/01
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Kevin Wolf, 2015/10/03
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Paolo Bonzini, 2015/10/04
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Jeff Cody, 2015/10/08
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Kevin Wolf, 2015/10/08
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Jeff Cody, 2015/10/08
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Kevin Wolf, 2015/10/08
- Re: [Qemu-devel] [PATCH 3/3] block: mirror - zero unallocated target sectors when zero init not present, Paolo Bonzini, 2015/10/08