On Wed, Mar 16, 2016 at 07:44:54PM +0200, Török Edwin wrote:
On 03/15/2016 21:34, Richard W.M. Jones wrote:
> I was looking at Clear Containers last week.
> [...]
>
> This is all very good analysis.
Thanks, looks like I raised the question at a good time :)
>
> The issues that I had in brief were:
>
> (1) We could run kvmtool, perhaps by adding a new backend, but it
> seems a better idea to add the required features to qemu. Anything
> based on kvmtool wouldn't support qcow2 and the myriad other features
> of qemu (see also:
>
https://rwmj.wordpress.com/2015/11/07/linux-kernel-library-backend-for-li...)
Could qemu-nbd from inside the guest be used? (as a
performance/security tradeoff)
There was also a proposed solution for using an [ordinary chroot-
style] container as the libguestfs appliance back in the day. It
involved qemu-nbd (on the host) plus loopback mounting IIRC. I don't
think anyone ever explored it in any depth, since it requires root and
as you say isn't secure.
> (2) On the kernel side, the Intel kernel contains lots of
little
> hacks, and many baremetal CONFIG_* options are disabled. Hacks can be
> upstreamed once we massage them into shape. The real issue is keeping
> a single baremetal + virt kernel image, since separate kernel images
> would never fly with Fedora or RHEL. That means we cannot just
> disable slow drivers/subsystems by having an alternate kernel with
> lots of CONFIG_* options disabled, we need to address those problems
> properly.
>
> (3) DAX / NVDIMM / etc - love them. Not supported upstream (either
> kernel or qemu) yet.
>
> (4) Passthrough (eg 9p) filesystems. You touched on that above.
> Red Hat doesn't much like 9pfs for several reasons, yet we also don't
> have a plausible alternative at the moment. This is mainly a problem
> for running fast Docker containers, rather than libguestfs though.
Another thought: why does guestfish need to boot the appliance more
than once? Could virsh save/restore or managedsave/stop/start be
used?
This was once proposed too. It requires a complete change to the way
we build and manage the appliance, and it was unclear if there would
be much benefit.
The guestfs appliance seems to be around 80MB saved [*] (perhaps
ballooning could help shrink this, or it could be compressed with lz4/lzop).
[*] I copied the XML and changed some things in it, cause the original failed to save
with: error: Requested operation is not valid: domain is marked for auto destroy
Rich.
--
Richard Jones, Virtualization Group, Red Hat
http://people.redhat.com/~rjones
Read my programming and virtualization blog:
http://rwmj.wordpress.com
virt-top is 'top' for virtual machines. Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top