Re: [Qemu-devel] [PATCH v3] block: Introduce "null" driver

[Eric Blake]

On 08/27/2014 11:53 PM, Fam Zheng wrote:
> This is an analogue to Linux null_blk. It can be used for testing block
> device emulation and general block layer functionalities such as
> coroutines and throttling, where disk IO is not necessary or wanted.
> 
> Use null:// for AIO version, and null-co:// for coroutine version.
> 
> Signed-off-by: Fam Zheng <address@hidden>
> 
> ---

> +++ b/qapi/block-core.json
> @@ -1150,7 +1150,8 @@
>    'data': [ 'archipelago', 'file', 'host_device', 'host_cdrom', 
> 'host_floppy',
>              'http', 'https', 'ftp', 'ftps', 'tftp', 'vvfat', 'blkdebug',
>              'blkverify', 'bochs', 'cloop', 'cow', 'dmg', 'parallels', 'qcow',
> -            'qcow2', 'qed', 'raw', 'vdi', 'vhdx', 'vmdk', 'vpc', 'quorum' ] }
> +            'qcow2', 'qed', 'raw', 'vdi', 'vhdx', 'vmdk', 'vpc', 'quorum',
> +            'null' ] }

As mentioned elsewhere, you probably want 'null' AND 'null-co'.  Bummer
that this list is mostly alphabetical, but that 'quorum' and 'null' are
out of order.

>  
>  ##
>  # @BlockdevOptionsBase
> @@ -1203,6 +1204,19 @@
>    'data': { 'filename': 'str' } }
>  
>  ##
> +# @BlockdevOptionsNull
> +#
> +# Driver specific block device options for the null backend.
> +#
> +# @size:    size of the device in bytes.

missing an #optional marker

> +#
> +# Since: 2.2
> +##
> +{ 'type': 'BlockdevOptionsNull',
> +  'base': 'BlockdevOptionsFile',
> +  'data': { '*size': 'int' } }
> +
> +##
>  # @BlockdevOptionsVVFAT
>  #
>  # Driver specific block device options for the vvfat protocol.
> @@ -1484,7 +1498,8 @@
>        'vhdx':       'BlockdevOptionsGenericFormat',
>        'vmdk':       'BlockdevOptionsGenericCOWFormat',
>        'vpc':        'BlockdevOptionsGenericFormat',
> -      'quorum':     'BlockdevOptionsQuorum'
> +      'quorum':     'BlockdevOptionsQuorum',
> +      'null':       'BlockdevOptionsNull'
>    } }
>  
>  ##
> 

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

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