[Libguestfs] Improving supermin appliance startup time (lkvm/qboot)

Török Edwin edwin+guestfs at etorok.net
Wed Mar 16 17:44:54 UTC 2016

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-libguestfs/)

Could qemu-nbd from inside the guest be used? (as a performance/security tradeoff)

> (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?

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

Best regards,
Edwin Török | Co-founder and Lead Developer

Skylable open-source object storage: reliable, fast, secure

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