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Date: Wed, 27 Nov 2013 11:22:22 +0800
From: Fam Zheng <famz@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v2 0/6] qemu-img: add preallocation=full
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To: Hu Tao <hutao@cn.fujitsu.com>, Kevin Wolf <kwolf@redhat.com>, "Daniel P. Berrange" <berrange@redhat.com>, Peter Lieven <pl@kamp.de>
Cc: qemu-devel@nongnu.org

On 2013=E5=B9=B411=E6=9C=8827=E6=97=A5 10:15, Hu Tao wrote:
> This series implements full image preallocation to create a non-sparse =
image
> file at creation time, both for raw and qcow2 format. The purpose is to=
 avoid
> performance deterioration of the guest cause by sparse image.
>
> This series implements full preallocation by using fallocate()/posix_fa=
llocate(),
> which have the advantage that it is fast when creating large image file.
> Zero-filling is not implemented, as writing zeros to image could be slo=
w for large
> file. (fallocate() ensures zero-filling, but posix_fallocate()) If user=
s want it,
> we can maybe add a option to let users have a choice. Suggestions?
>

We have zero init in raw-posix:

static BlockDriver bdrv_file =3D {
     ...
     .bdrv_has_zero_init =3D bdrv_has_zero_init_1,
}

so I think we have to zero-fill it if posix_fallocate doesn't ensure.

Fam

> Base on Kevin's patch at:
> http://lists.gnu.org/archive/html/qemu-devel/2011-01/msg03017.html
>
> Hu Tao (6):
>    block: introduce prealloc_mode
>    block: add BlockDriver.bdrv_preallocate.
>    block/raw-posix: implement bdrv_preallocate
>    raw-posix: Add full image preallocation option
>    qcow2: implement bdrv_preallocate
>    qcow2: Add full image preallocation option
>
>   block.c                   | 13 +++++++++++
>   block/qcow2.c             | 32 +++++++++++++++++++++------
>   block/raw-posix.c         | 56 ++++++++++++++++++++++++++++++++++++++=
+++++++++
>   include/block/block.h     |  7 ++++++
>   include/block/block_int.h |  3 +++
>   5 files changed, 104 insertions(+), 7 deletions(-)
>