Bug 526869

Summary:	Add virtio_blk support cache flush (VIRTIO_BLK_F_FLUSH)
Product:	[Fedora] Fedora	Reporter:	Mark McLoughlin <markmc>
Component:	kernel	Assignee:	Justin M. Forbes <jforbes>
Status:	CLOSED RAWHIDE	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	high
Version:	rawhide	CC:	amit.shah, chellwig, dougsland, gansalmon, itamar, kernel-maint, virt-maint
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2009-10-06 14:45:45 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	498969

Description Mark McLoughlin 2009-10-02 08:23:07 UTC

See discussion in bug #525890

We should backport:

  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=f1b0ef0626

  virtio_blk: add support for cache flush

  Recent qemu has added a VIRTIO_BLK_F_FLUSH flag to advertise that the
  virtual disk has a volatile write cache that needs to be flushed.  In case
  we see this feature implement tell the Linux block layer about the fact
  and use the new VIRTIO_BLK_T_FLUSH to flush the cache when required.  This
  allows for an correct and simple implementation of write barriers.

This mail from Christoph is a good writeup on the background:

  http://www.mail-archive.com/kvm@vger.kernel.org/msg21559.html

We should get this into F-12 GA even if qemu doesn't yet support it in F-12 so that F-12 guest installer kernels have this feature.

Comment 1 Justin M. Forbes 2009-10-06 14:45:45 UTC

This has been added to the F-12 kernel and should be available in the next kernel tagged.