From: Kevin Wolf <kwolf@redhat.com>
To: qemu-block@nongnu.org
Cc: nsoffer@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com
Subject: Re: [PATCH for-5.1 v2 1/2] qcow2: Implement v2 zero writes with discard if possible
Date: Tue, 21 Jul 2020 16:28:36 +0200 [thread overview]
Message-ID: <20200721142836.GD18481@linux.fritz.box> (raw)
In-Reply-To: <20200721135520.72355-2-kwolf@redhat.com>
Am 21.07.2020 um 15:55 hat Kevin Wolf geschrieben:
> 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>
Oops, forgot to apply this from v1:
Reviewed-by: Max Reitz <mreitz@redhat.com>
The patch is unchanged, so I'll include this when applying.
Kevin
next prev parent reply other threads:[~2020-07-21 14:29 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-21 13:55 [PATCH for-5.1 v2 0/2] qemu-img convert -n: Keep qcow2 v2 target sparse Kevin Wolf
2020-07-21 13:55 ` [PATCH for-5.1 v2 1/2] qcow2: Implement v2 zero writes with discard if possible Kevin Wolf
2020-07-21 14:28 ` Kevin Wolf [this message]
2020-07-21 13:55 ` [PATCH for-5.1 v2 2/2] iotests: Test sparseness for qemu-img convert -n Kevin Wolf
2020-07-21 15:23 ` Max Reitz
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