Re: [Qemu-devel] [PATCH v3 4/8] add mode field to blockdev-snapshot-sync transaction item

[Eric Blake]

On 03/05/2012 10:33 AM, Paolo Bonzini wrote:
> The mode field lets a management application create the snapshot
> destination outside QEMU.
> 
> Right now, the only modes are "existing" and "absolute-paths".  Mirroring
> introduces "no-backing-file".  In the future "relative-paths" could be
> implemented too.
> 
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
>  blockdev.c       |   25 ++++++++++++++++---------
>  qapi-schema.json |   21 ++++++++++++++++++++-
>  qmp-commands.hx  |   10 ++++++++++
>  3 files changed, 46 insertions(+), 10 deletions(-)
> 

>  
>  ##
> +# @NewImageMode
> +#
> +# An enumeration that tells QEMU how to set the backing file path in
> +# a new image file.
> +#
> +# @existing: QEMU should look for an existing image file.
> +#
> +# @absolute-paths: QEMU should create a new image with absolute paths
> +# for the backing file.
> +#
> +# @no-backing-file: QEMU should create a new image with no backing file.

Not present in this patch.  Does it need to be rebased into the correct
part of the series?

> +#
> +# Since: 1.1
> +##
> +{ 'enum': 'NewImageMode'
> +  'data': [ 'existing', 'absolute-paths' ] }
> +
> +##
>  # @BlockdevSnapshot
>  #
>  # @device:  the name of the device to generate the snapshot from.
> @@ -1127,7 +1145,8 @@
>  # @format: #optional the format of the snapshot image, default is 'qcow2'.
>  ##
>  { 'type': 'BlockdevSnapshot',
> -  'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str' } }
> +  'data': { 'device': 'str', 'snapshot-file': 'str', '*format': 'str',
> +            '*mode': 'NewImageMode' } }
>  
>  ##
>  # @BlockdevAction
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index fb4f1df..7c03b62 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -705,6 +705,13 @@ A list of dictionaries is accepted, that contains the 
> actions to be performed.
>  For snapshots this is the device, the file to use for the new snapshot,
>  and the format.  The default format, if not specified, is qcow2.
>  
> +Each new snapshot defaults to being created by QEMU (wiping any
> +contents if the file already exists),

so this is mode of 'absolute-paths', which is the default if mode is not
present,

> but it is also possible to reuse
> +an externally-created file.  In the latter case, you should ensure that
> +the new image file has the same contents as the current one; QEMU cannot
> +perform any meaningful check.  Typically this is achieved by using the
> +current image file as the backing file for the new image.

and this is mode 'existing'.  Correct?  If so, let's actually call that
out in the wording.

> +
>  Arguments:
>  
>  actions array:
> @@ -715,6 +722,8 @@ actions array:
>        - "device": device name to snapshot (json-string)
>        - "snapshot-file": name of new image file (json-string)
>        - "format": format of new image (json-string, optional)
> +      - "mode": whether and how QEMU should create the snapshot file
> +        (NewImageMode, optional, default "absolute-paths")

Well, this solves one of my two comments about the above wording, by
calling out the default.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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