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Re: [Qemu-devel] [PATCH v2] qapi: converted commit

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v2] qapi: converted commit
Date: Thu, 14 Jun 2012 06:18:07 -0600
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On 06/14/2012 01:35 AM, Pavel Hrdina wrote:
> Signed-off-by: Pavel Hrdina <address@hidden>
> ---

> +++ b/qapi-schema.json
> @@ -1169,6 +1169,21 @@
>  { 'command': 'block_resize', 'data': { 'device': 'str', 'size': 'int' }}
>  ##
> +# @commit
> +#
> +# Commit changes to the disk images (if -snapshot is used) or backing files.
> +#
> +# @device: the name of the device or the "all" to commit all devices
> +#
> +# Returns: nothing on success
> +#          If @device is not a valid block device, DeviceNotFound
> +#          If a long-running operation is using the device, DeviceInUse
> +#
> +# Since: 1.2
> +##
> +{ 'command': 'commit', 'data': { 'device': 'str' }}

Should we use this as an opportunity to make the command more powerful?
 For example, integrating this with the 'transaction' command or a block
job queried by 'query-block-jobs' to track its progress would be useful.
 Also, suppose I have A <- B <- C.  Does 'commit' only do one layer (C
into B), or all layers (B and C into A)?  That argues that we need an
optional parameter that says how deep to commit (committing C into B
only to repeat and commit B into A is more time-consuming than directly
committing both B and C into A to start with).  When a commit is
complete, which file is backing the device - is it still C (which
continues to diverge, but now from the point of the commit) or does qemu
pivot things to have the device now backed by B (and C can be discarded,
particularly true if changes are now going into B which invalidate C).

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

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