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** Tags added: compute

** Tags added: libvirt security

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https://bugs.launchpad.net/bugs/1350766

Title:
  Race condition: compute intermittently corrupts base images on
  download from glance

Status in OpenStack Compute (Nova):
  New

Bug description:
  Under certain conditions, which I happen to meet often on my Icehouse
  single node setup, uploaded images or snapshots fail to boot. See also
  https://ask.openstack.org/en/question/42804/icehouse-how-to-boot-a
  -snapshot-from-a-running-instance/

  Reason: When first instantiating a QCOW2 image, it's

  (1)  downloaded as QCOW2 to /var/lib/nova/instances/_base/IMAGEID.part
  (2)  converted to RAW format base /var/lib/nova/instances/_base/IMAGEID.converted using qemu-img

  The step (1) is performed in nova/image/glance.py,
  GlanceImageService.download using buffered IO, which does not
  guarantee the resulting data to be written to disk on file close.
  Consequently, the source image file may not be written completely when
  qemu-img sub-process starts reading in step (2). Whether the result is
  good or bad depends on speed of download, file size, and how quickly
  qemu-image can digest its input.

  Proposed fix: enforce fsync on output File object before returning
  from download. Patch attached.

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