Re: Adding QCOW2 reading/writing support

[Manuel Bentele <manuel-bentele@web.de>]

Hi,

On 5/14/19 4:28 PM, Roman Penyaev wrote:
> On 2019-04-17 23:53, Manuel Bentele wrote:
>
> [cut]
>
>> If you have an idea to solve the opposition for file formats that are
>> acting as a container or virtual disk node for various data, please let
>> me know.
>
> If you need a raw block device you can export qcow2 image as a network
> block
> device, something as the following:
>
> # modprobe nbd
> # qemu-nbd --connect=/dev/nbd0 image.qcow2
> # fdisk -l /dev/nbd0
>
> I suppose simplest variant.
>
> --
> Roman

Thanks for your suggestion. We already discussed this during a project
meeting. Some time ago, I have summarized that already (sorry for the
diverging conversation of this topic on the mailinglist).
All in all, the crucial point is the performance:

> [...]
>
> A workaround for that problem could be the local usage of nbd to include
> the QCOW2 disk image as block device, but it involves a lot of
> interaction between user and kernel space and thus an decreasing
> performance. That leads to the motivation to implement the reading of
> QCOW2 disk images directly in the kernel and aim for an merge into the
> mainline kernel source to avoid out-of-kernel-tree maintenance.
>
> [...]

--
Manuel