Re: [Qemu-devel] [PATCH v4 9/9] qapi: Add transaction support to dirty-bitmap-{add, disable}

[Eric Blake]

On 03/27/2014 03:09 AM, Fam Zheng wrote:
> This adds dirty-bitmap-add and dirty-bitmap-disable to transactions.
> With this, user can stop a dirty bitmap, start backup of it, and start
> another dirty bitmap atomically, so that the dirty bitmap is tracked
> incrementally and we don't miss any write.

Ah, this addresses my question in 7/9 about atomicity of creating a map
in disabled state.  Nice idea to use 'transaction' to merge the two
commands, instead of having to bloat the creation with ever more options.

> 
> Signed-off-by: Fam Zheng <address@hidden>
> ---
>  blockdev.c       | 68 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  qapi-schema.json |  4 +++-
>  2 files changed, 71 insertions(+), 1 deletion(-)
> 
> +++ b/qapi-schema.json
> @@ -1994,7 +1994,9 @@
>         'blockdev-snapshot-sync': 'BlockdevSnapshot',
>         'drive-backup': 'DriveBackup',
>         'abort': 'Abort',
> -       'blockdev-snapshot-internal-sync': 'BlockdevSnapshotInternal'
> +       'blockdev-snapshot-internal-sync': 'BlockdevSnapshotInternal',
> +       'dirty-bitmap-add': 'DirtyBitmap',
> +       'dirty-bitmap-disable': 'DirtyBitmap'
>     } }

However, shouldn't it ALSO be possible to enable a bitmap in tandem with
other transaction operations?  I can imagine a transaction that both
kicks off a snapshot and enables a bitmap that was previously added but
left disabled.

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

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