From: Max Reitz <mreitz@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org
Cc: nsoffer@redhat.com, qemu-devel@nongnu.org
Subject: Re: [PATCH for-5.1 1/2] qcow2: Implement v2 zero writes with discard if possible
Date: Tue, 21 Jul 2020 12:07:09 +0200 [thread overview]
Message-ID: <ce2aea36-5490-440c-761e-9febd9f7480a@redhat.com> (raw)
In-Reply-To: <20200720131810.177978-2-kwolf@redhat.com>
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On 20.07.20 15:18, Kevin Wolf wrote:
> qcow2 version 2 images don't support the zero flag for clusters, so for
> write_zeroes requests, we return -ENOTSUP and get explicit zero buffer
> writes. If the image doesn't have a backing file, we can do better: Just
> discard the respective clusters.
>
> This is relevant for 'qemu-img convert -O qcow2 -n', where qemu-img has
> to assume that the existing target image may contain any data, so it has
> to write zeroes. Without this patch, this results in a fully allocated
> target image, even if the source image was empty.
>
> Reported-by: Nir Soffer <nsoffer@redhat.com>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
> block/qcow2-cluster.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
Reviewed-by: Max Reitz <mreitz@redhat.com>
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next prev parent reply other threads:[~2020-07-21 10:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-20 13:18 [PATCH for-5.1 0/2] qemu-img convert -n: Keep qcow2 v2 target sparse Kevin Wolf
2020-07-20 13:18 ` [PATCH for-5.1 1/2] qcow2: Implement v2 zero writes with discard if possible Kevin Wolf
2020-07-20 14:50 ` Nir Soffer
2020-07-21 10:07 ` Max Reitz [this message]
2020-07-22 17:01 ` Maxim Levitsky
2020-07-22 17:14 ` Kevin Wolf
2020-07-22 17:15 ` Maxim Levitsky
2020-07-20 13:18 ` [PATCH for-5.1 2/2] iotests: Test sparseness for qemu-img convert -n Kevin Wolf
2020-07-20 14:47 ` Nir Soffer
2020-07-21 13:49 ` Kevin Wolf
2020-07-21 10:19 ` Max Reitz
2020-07-21 11:20 ` Kevin Wolf
2020-07-21 11:25 ` Max Reitz
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