Re: [libvirt] [PATCH 2/2] storage: Check qemu-img encryption type capability
On 04/18/2018 08:17 AM, Daniel P. Berrangé wrote:
On Wed, Apr 18, 2018 at 08:08:41AM -0400, John Ferlan wrote:
>
>
> On 04/18/2018 04:29 AM, Daniel P. Berrangé wrote:
>> On Tue, Apr 17, 2018 at 03:23:33PM -0400, John Ferlan wrote:
>>> https://bugzilla.redhat.com/show_bug.cgi?id=1526382
>>>
>>> As of QEMU 2.9, qemu-img has enforced using the "key-secret" for
>>> creation of encrypted volumes. That is, LUKS encryption is now
>>> required and the old (awful) qcow[2] encryption methodolgy is
>>> no longer supported.
>>
>> Not quite right actually. The 'key-secret' approach can be used to
>> create both LUKS and the old qcow[2] encryption.
>>
>> We only forbid qcow[2] encryption with the system emulators, still
>> have full support in qemu-img for sake of interoperability. The only
>> break there was the command line syntax
>>
>
> Oh, OK - well I didn't find that to be obvious... So there is a way
> using secret objects to create a qcow[2] encrypted volume?
Sure, the exact same syntax as with luks volumes - you just specify
"qcow" instead of "luks" as the type.
> Still Jano has NACK'd using help scraping (and posted a separate series
> removing it completely).
>
> So then the question becomes does this change "convert" into a disallow
> this type of creation going forward? Do we just cause failure in
> storageBackendCreateQemuImgCheckEncryption when not using LUKS or do we
> let the qemu-img just be the bad guy and do nothing in our code?
QEMU is likely to support the qcow2 enc format indefinitely, but only
in the qemu-img tool for the sake of data liberation. I don't think
libvirt should arbitrarily decide to drop it from our qemu-img
usage.
So that means Jano's series to remove help scraping completely cannot be
applied since this code would need to check that the option exists
before using it; otherwise, anything inclusive of QEMU 1.5 and 2.9 would
fail (the option was introduced in 2.10 - I mistyped above).
What could be applied would be the removal of OPTIONS and
OPTIONS_COMPAT, but this new one would need to exist since AFAIK there
is no other way currently to query qemu-img for what it supports.
Going to make for some ugly code...
John
>>> + if (imgformat >= QEMU_IMG_BACKING_FORMAT_OPTIONS_KEY_SECRET) {
>>> + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
>>> + _("qemu-img no longer supports qcow
encryption, "
>>> + "use LUKS encryption instead"));
>>> + return -1;
>>> + }
>>
>> Why is imgformat being compared against
QEMU_IMG_BACKING_FORMAT_OPTIONS_KEY_SECRET ?
>>
>> Aren't those two sides of the expression from completely different
>> enum types.
>>
>
> Although perhaps not well named, @imgformat is fetched via
> virStorageBackendQEMUImgBackingFormat which returns
> QEMU_IMG_BACKING_FORMAT_OPTIONS* type enum's.
Regards,
Daniel