Re: [Qemu-devel] [PATCH V6 1/3] Implement sync modes for drive-backup.

[Eric Blake]

On 07/24/2013 04:55 AM, Kevin Wolf wrote:

> Unconditionally overriding format for NEW_IMAGE_MODE_EXISTING is
> definitely wrong. It's the user's choice which COW format to use for the
> backup image. There's no reason why it has to be the same format as the
> image that is being backed up.
> 
> Before, bs->drv->format_name was a default for the case where a new
> image had to be created and no format was given; and the format of
> existing images could be probed. This is still what makes most sense to
> me. What's even the goal with this change?

Furthermore, I'm proposing that for 1.6, we should make the format
argument mandatory for drive-backup.  We made it optional for
drive-mirror, to allow for probing, but there have been CVEs in the past
due to probing of a raw file gone wrong.  We can always relax a
mandatory argument into an optional one in 1.7, if we decide that
probing can be done safely, but we can never turn an optional argument
into a mandatory one once the initial release bakes in the option.  It
would make the code a lot simpler to just have a mandatory format
argument, instead of having to bake in and document hueristics on which
format is picked when the caller doesn't provide one.

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

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