Bug 832194

Summary:	make <transient> tag in libvirt work for qemu disks
Product:	[Community] Virtualization Tools	Reporter:	Jonathan Blandford <jrb>
Component:	libvirt	Assignee:	Eric Blake <eblake>
Status:	CLOSED DUPLICATE	QA Contact:
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	unspecified	CC:	amit.shah, crobinso, cwei, ddumas, deepakcs, dyuan, eblake, jprokes, mzhan, rbalakri, shyu, socketpair
Target Milestone:	---
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
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Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:
Clones:	1040068 (view as bug list)		Environment:
Last Closed:	2016-03-21 22:59:53 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1040068

Description Jonathan Blandford 2012-06-14 19:49:12 UTC

It would be great to have a <transient> tag in libvirt's xml format so that we could specify that a disk isn't modified.  That is to say, we could boot into a snapshot of a VM, use it for the duration of a session, and then discard it when done.  This would be great for untrusted VMs, as well as demos.

Comment 1 Eric Blake 2012-06-14 19:54:20 UTC

Actually, we already _do_ have a <transient> tag supported in the XML, since 0.9.5, it's just that it never got wired up to being supported in qemu.

Comment 3 Eric Blake 2013-08-05 13:53:06 UTC

Revisiting this issue - still something we want, but it may first be useful to have the notion of a storage pool associated with a domain, where libvirt allocates from that storage pool instead of from /tmp when creating wrapper files (since /tmp may be small, especially on tmp-on-tmpfs systems)

Comment 4 Коренберг Марк 2015-09-04 11:44:49 UTC

maybe do that:


1. <transient pool=xxxx>
2. Fail if pool type is not a directory
3. Fail if multiple disks defined with <transient> that points to different pools
4. pass TMP environment variable for qemu to a directory where that pool points to?


Also, I can try to make patch to QEMU project in order to allow specify directory as:

qemu-system-xxx ... -drive snapshot=on,snapshot_dir=...

Also, 

<qemu:commandline>
     <qemu:arg value='-snapshot'/>
</qemu:commandline>

does not work now with error:

internal error: process exited while connecting to monitor: qemu-system-x86_64: -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1: Device needs media, but drive is empty
qemu-system-x86_64: -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1: Device initialization failed.
qemu-system-x86_64: -device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1: Device 'ide-hd' could not be initialized


So, after my patch for QEMU, it seems, that <transient> will not work anyway.

Comment 5 Коренберг Марк 2015-09-04 11:46:32 UTC

Forgot to add, if my patch will go to upstream in QEMU, constraints 3 and 4 should be removed

Comment 6 Cole Robinson 2016-03-21 22:59:53 UTC

marking as duplicate of an older bug for this feature

*** This bug has been marked as a duplicate of bug 508662 ***