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Bug 1227354 - [virtio-1] Disabling Virtio-1 from Libvirt
Summary: [virtio-1] Disabling Virtio-1 from Libvirt
Keywords:
Status: CLOSED DEFERRED
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: libvirt
Version: 7.2
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: ---
Assignee: Ján Tomko
QA Contact: Han Han
URL:
Whiteboard:
Depends On: 1227343
Blocks: 1288337 1365823
TreeView+ depends on / blocked
 
Reported: 2015-06-02 13:18 UTC by Amnon Ilan
Modified: 2018-08-09 07:10 UTC (History)
17 users (show)

Fixed In Version:
Doc Type: Enhancement
Doc Text:
Clone Of:
Environment:
Last Closed: 2017-05-22 17:38:33 UTC
Target Upstream Version:
Embargoed:


Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Bugzilla 1614127 1 None None None 2021-03-30 10:59:48 UTC

Internal Links: 1614127

Description Amnon Ilan 2015-06-02 13:18:22 UTC
Description of problem:

Control 'disable-modern' and 'disable-legacy' flags for all virtio devices
Required in order to avoid compatibility issues.

Version-Release number of selected component (if applicable):


How reproducible:


Steps to Reproduce:
1.
2.
3.

Actual results:


Expected results:


Additional info:

Comment 1 Daniel Berrangé 2015-06-02 13:23:46 UTC
(In reply to Amnon Ilan from comment #0)
> Description of problem:
> 
> Control 'disable-modern' and 'disable-legacy' flags for all virtio devices
> Required in order to avoid compatibility issues.

What compatibility issues ?  IIUC, QEMU ought to negotiate the right settings for virtio with the guest OS. Adding these flags to libvirt XML for guests seems like quite a unpleasant thing to do.

Comment 3 Amnon Ilan 2015-07-08 17:36:10 UTC
In 7.3 the default Virtio mode will be "transitional": both legacy and modern are enabled. Since "modern" (Virtio 1) is new, there may be some issues that will not 
be discovered by QE. In such a case we can run into problems if we have no way 
to force the driver to "legacy" mode. That is why 'disable-modern' is important. 
Now for the imprtance of 'disable-legacy' (less important, but yet): when we wish to boot from a virtio device and the device is in legacy mode, the device will require io space, and this space is very limited (as an example, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1175124 ).
In such cases we would like to do 'disable-legacy' since Virtio 1 does not require the io space.
Both cases are related to customer usage and not only testing (where qemu command-line could do the job).

Comment 5 Ján Tomko 2016-07-29 13:38:34 UTC
Proposed upstream patches:
https://www.redhat.com/archives/libvir-list/2016-July/msg01235.html

Comment 9 Ján Tomko 2016-09-07 16:12:30 UTC
The upstream design is still not settled:
https://www.redhat.com/archives/libvir-list/2016-September/msg00228.html

Comment 11 Ján Tomko 2017-05-22 17:38:33 UTC
Per:
https://www.redhat.com/archives/libvir-list/2016-September/msg00227.html
it would be nicer not to expose this in the XML unless really needed.


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