[libvirt] [Qemu-devel] live snapshot wiki updated

Blue Swirl blauwirbel at gmail.com
Thu Jul 21 19:34:29 UTC 2011

On Thu, Jul 21, 2011 at 11:07 AM, Jes Sorensen <Jes.Sorensen at redhat.com> wrote:
> On 07/20/11 21:51, Blue Swirl wrote:
>>> And the snapshot_blkdev monitor command is a case where qemu needs to create
>>> > a new qcow2 image on the fly, while referencing the name of an existing
>>> > file.  What backing name do you put in the new qcow2 file unless you already
>>> > have a name association for all fds already open for the existing backing
>>> > file?
>> For backing file with original name of "/path/in/storage", QEMU could
>> present the fd and the backin path by requesting something like
>> "fd:12,/path/in/storage". The next file in chain "/path2/file" would
>> be "fd:12,fd:34,/path2/file". Or if possible, -fd 12 -backing
>> /path/in/storage with spaces and funny characters escaped etc.
> Rather than trying to do this by mangling files on the disk, I would
> suggest we allow registering a call-back open function, which calls back
> into libvirt and requests it to open a given file. It can then do all
> it's security foo to decide whether or not to allow the file to be open.

Just to clarify: I was not proposing any mangling of the files.

> This is relatively clean and avoids the mess of relying on outside
> processes messing about in the images.
> Cheers,
> Jes

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