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[Qemu-devel] [Bug 1368815] Change abandoned on cinder (master)

From: OpenStack Infra
Subject: [Qemu-devel] [Bug 1368815] Change abandoned on cinder (master)
Date: Fri, 08 May 2015 22:29:45 -0000

Change abandoned by Mike Perez (address@hidden) on branch: master
Review: https://review.openstack.org/143575
Reason: No activity for over a month.

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  qemu-img convert intermittently corrupts output images

Status in Cinder:
Status in OpenStack Compute (Nova):
  Won't Fix
Status in QEMU:
  In Progress
Status in qemu package in Ubuntu:
  Fix Released
Status in qemu source package in Trusty:
  Fix Released
Status in qemu source package in Utopic:
  Fix Released
Status in qemu source package in Vivid:
  Fix Released

Bug description:
  Impact: occasional image corruption (any format on local filesystem)
  Test case: see the qemu-img command below
  Regression potential: this cherrypicks a patch from upstream to a 
not-insignificantly older qemu source tree.  While the cherrypick seems sane, 
it's possible that there are subtle interactions with the other delta.  I'd 
really like for a full qa-regression-test qemu testcase to be run against this 

  -- Found in releases qemu-2.0.0, qemu-2.0.2, qemu-2.1.0. Tested on
  Ubuntu 14.04 using Ext4 filesystems.

  The command

    qemu-img convert -O raw inputimage.qcow2 outputimage.raw

  intermittently creates corrupted output images, when the input image
  is not yet fully synchronized to disk. While the issue has actually
  been discovered in operation of of OpenStack nova, it can be
  reproduced "easily" on command line using

    cat $SRC_PATH > $TMP_PATH && $QEMU_IMG_PATH convert -O raw $TMP_PATH
  $DST_PATH && cksum $DST_PATH

  on filesystems exposing this behavior. (The difficult part of this
  exercise is to prepare a filesystem to reliably trigger this race. On
  my test machine some filesystems are affected while other aren't, and
  unfortunately I haven't found the relevant difference between them,
  yet. Possible it's timing issues completely out of userspace control

  The root cause, however, is the same as in


  and it can be solved the same way as suggested in


  In qemu, file block/raw-posix.c use the FIEMAP_FLAG_SYNC, i.e change

      f.fm.fm_flags = 0;


      f.fm.fm_flags = FIEMAP_FLAG_SYNC;

  As discussed in the thread mentioned above, retrieving a page cache
  coherent map of file extents is possible only after fsync on that

  See also


  In that bug report filed against nova, fsync had been suggested to be
  performed by the framework invoking qemu-img. However, as the choice
  of fiemap -- implying this otherwise unneeded fsync of a temporary
  file  -- is not made by the caller but by qemu-img, I agree with the
  nova bug reviewer's objection to put it into nova. The fsync should
  instead be triggered by qemu-img utilizing the FIEMAP_FLAG_SYNC,
  specifically intended for that purpose.

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