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Re: [Qemu-block] [PATCH 0/3] qemu-img: Allow rebase with no input base
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH 0/3] qemu-img: Allow rebase with no input base |
Date: |
Wed, 6 Feb 2019 16:35:48 +0100 |
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Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
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On 13.07.18 13:14, Max Reitz wrote:
> This series allows using qemu-img rebase on images that do not have a
> backing file. Right now, this fails with the rather cryptic error
> message:
>
> $ qemu-img rebase -b base.qcow2 foo.qcow2
> qemu-img: Could not open old backing file '': The 'file' block driver
> requires a file name
>
> Yeah, well, OK.
>
> With how rebase currently works, this would lead to the overlay being
> filled with zeroes, however. This is where patch 2 comes in and instead
> makes rebase use blk_pwrite_zeroes() whenever it handles an area past
> the input’s backing file’s EOF.
>
> (Note that additionally we could try to punch holes in the overlay
> whenever it matches the new backing file, but that’s something I’ll put
> off for later. (We don’t even have a reliable method for punching holes
> into an overlay yet, although I would like to have such because it could
> make active commit more efficient.))
>
>
> And patch 3 adds the usual test.
>
>
> Max Reitz (3):
> qemu-img: Allow rebase with no input base
> qemu-img: Use zero writes after source backing EOF
> iotests: Add test for rebase without input base
>
> qemu-img.c | 72 +++++++++++++++++++++++---------------
> tests/qemu-iotests/024 | 70 ++++++++++++++++++++++++++++++++++++
> tests/qemu-iotests/024.out | 37 ++++++++++++++++++++
> 3 files changed, 150 insertions(+), 29 deletions(-)
>
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