Re: [Qemu-devel] [RFC PATCH v2 0/6] qemu-img: add preallocation=full

[Fam Zheng]

On 2013年11月27日 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_fallocate(),
> 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 slow for 
> large
> file. (fallocate() ensures zero-filling, but posix_fallocate()) If users 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 = {
    ...
    .bdrv_has_zero_init = 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(-)