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Re: [Qemu-devel] [PATCH V4 5/5] block: make all steps in qmp_transaction

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH V4 5/5] block: make all steps in qmp_transaction() as callback
Date: Fri, 03 May 2013 08:46:38 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130402 Thunderbird/17.0.5

On 05/01/2013 08:26 PM, Wenchao Xia wrote:
> Make it easier to add other operations to qmp_transaction() by using
> callbacks, with external snapshots serving as an example implementation
> of the callbacks.
> Signed-off-by: Wenchao Xia <address@hidden>
> ---
>  blockdev.c |   92 ++++++++++++++++++++++++++++++++++++++++++++++-------------
>  1 files changed, 71 insertions(+), 21 deletions(-)

> +/*
> + * This structure must be arranged as first member in parent type, assuming

To me, "parent type" seems like the wrong relationship - in C++, the
parent type is the smaller type, and the child type is the larger type
that includes the parent type as its first member.  That is,
BlkTransationStates IS the parent type, and the comment would read
better as "first member in child type".

> + * that compiler will also arrange it to the same address with parent 
> instance.
> + * Later it will be used in free().
> + */
> +struct BlkTransactionStates {
> +    BlockdevAction *action;
> +    const BdrvActionOps *ops;
> +    QSIMPLEQ_ENTRY(BlkTransactionStates) entry;
> +};

>      /* Now we are going to do the actual pivot.  Everything up to this point
>       * is reversible, but we are committed at this point */

Is this comment still correct, now that things are extensible, or should
you s/pivot/commit/?

If you do respin, I agree that s/rollback/abort/ might be a nicer name
for that particular callback.  But I'm also quite okay with using the
patch as-is without a respin (while I pointed out two possible comment
wording changes, they don't make or break the patch for me).

Reviewed-by: Eric Blake <address@hidden>

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

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