Re: [Qemu-devel] [PATCH 3/5] block: Remove cache.writeback from blockdev-add

[Eric Blake <eblake@redhat.com>]

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On 03/14/2016 09:44 AM, Kevin Wolf wrote:
> The WCE bit is a frontend property and should not be part of the backend
> configuration. This is especially important because the same BDS can be
> used by different users with different WCE requirements.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  qapi/block-core.json | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index 9bf1b22..e3617e2 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -1614,7 +1614,6 @@
>  #
>  # Includes cache-related options for block devices
>  #
> -# @writeback:   #optional enables writeback mode for any caches (default: true)
>  # @direct:      #optional enables use of O_DIRECT (bypass the host page cache;
>  #               default: false)
>  # @no-flush:    #optional ignore any flush requests for the device (default:
> @@ -1623,8 +1622,7 @@
>  # Since: 1.7
>  ##
>  { 'struct': 'BlockdevCacheOptions',
> -  'data': { '*writeback': 'bool',
> -            '*direct': 'bool',
> +  'data': { '*direct': 'bool',
>              '*no-flush': 'bool' } }

Observable through introspection.  Not quite backwards-compatible, but
at least clients can learn about it, and arguably clients shouldn't have
been using it.  I can accept it as a bug fix, even though it does risk
breaking old clients that were trying to use it.

If it helps, libvirt does not seem to have been using it.

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


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