Re: [Qemu-devel] [PATCH] qcow2: Flush image after creation

[Eric Blake]

On 10/23/2013 08:40 PM, Max Reitz wrote:
> Opening the qcow2 image with BDRV_O_NO_FLUSH prevents any flushes during
> the image creation. This means that the image has not yet been flushed
> to disk when qemu-img create exits. This flush is delayed until the next
> operation on the image involving opening it without BDRV_O_NO_FLUSH and
> closing (or directly flushing) it. For large images and/or images with a
> small cluster size and preallocated metadata, this flush may take a
> significant amount of time and may occur unexpectedly.
> 
> Reopening the image without BDRV_O_NO_FLUSH right before the end of
> qcow2_create2() results in preponing the potentially costly flush into

s/preponing/hoisting/

> the image creation, which is expected to take some time (whereas
> successive image operations may be not).
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/qcow2.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <address@hidden>

> -    ret = 0;
> +    bdrv_close(bs);
> +
> +    /* Reopen the image without BDRV_O_NO_FLUSH to flush it before returning 
> */
> +    ret = bdrv_open(bs, filename, NULL,
> +        BDRV_O_RDWR | BDRV_O_CACHE_WB, drv, &local_err);

I would probably have indented as:

ret = bdrv_open(bs, filename, NULL,
                BDRV_O_RDWR | BDRV_O_CACHE_WB,
                drv, &local_err);

but it's trivial enough that I'm also fine with your choice.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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