Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] ignore bdrv_flush operation when no qcow2 cache item is dirty

[Eric Blake <eblake@redhat.com>]

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[patches should always be sent to qemu-devel, even if qemu-block is also
in the to/cc list]

On 07/08/2015 01:26 AM, Qingshu Chen wrote:
> qcow2_cache_flush() writes dirty cache to the disk and invokes bdrv_flush()
> to make the data durable. But even if there is no dirty cache,
> qcow2_cache_flush() would invoke bdrv_flush().  In fact, bdrv_flush() will
> invoke fdatasync(), and it is an expensive operation. The patch will not
> invoke bdrv_flush if there is not dirty cache. The reason that I modify the
> return value of qcow2_cache_flush()  is qcow2_co_flush_to_os needs to know
> whether flush operation is called. Following is the patch:
> 
>>From 23f9f83da4178e8fbb53d2cffe128f5a2d3a239a Mon Sep 17 00:00:00 2001
> From: Qingshu Chen <qingshu.chen714@gmail.com>
> Date: Wed, 1 Jul 2015 14:45:23 +0800
> Subject: [PATCH 1/2] ignore bdrv_flush operation when no qcow2 cache item is
>  dirty
> Signed-off-by: Qingshu Chen <qingshu.chen714@gmail.com>

I didn't quickly find an associated 2/2 patch; are you sure you sent the
series correctly?

> 
> ---
>  block/qcow2-cache.c | 9 ++++++++-
>  block/qcow2.c       | 2 ++
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
> index ed92a09..57c0601 100644
> --- a/block/qcow2-cache.c
> +++ b/block/qcow2-cache.c
> @@ -174,6 +174,7 @@ int qcow2_cache_flush(BlockDriverState *bs, Qcow2Cache
> *c)
>      int result = 0;
>      int ret;
>      int i;
> +    int flag = 0;

This is used as a bool, so declare it as such (bool flag = false;).

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


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