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[Pasquale Porreca <pasquale.porreca@xxxxxxxxxxxxxx>]

Public bug reported:

I came across this issue for a simple typo in virt_type parameter in the
file nova-compute.conf (same results if the parameter is defined in
nova.conf) where I wrote:

[libvirt]
virt_type = quemu

instead of "qemu".

In the Horizon dashboard this lead to an error with explanation "Failure
to prepping block device" (see image in attach), not only useless, but
misleading since I thought about a problem with cinder.

Also the log file nova-compute.log was not so clear (see text file in
attach): once again "Failure prepping block device" with the addition of
this info: "NovaException: Unable to determine disk prefix for None".

Only analyzing the python code of the file in the traceback of the log
(nova/compute/manager.py, nova/virt/libvirt/driver.py,
nova/virt/libvirt/blockinfo.py) I could understand that the disk prefix
(i.e. vd/hs/sd) is indeed bound to CONF.libvirt.virt_type (i.e.
virt_type parameter in nova.conf).

Configuration files can be modified by operators and I don't think they
should have to look at the code to get a clue of what is going on,
especially for an error that can be simply (at least this is my first
impression) caught and tracked.

** Affects: nova
     Importance: Undecided
         Status: New


** Tags: compute

** Attachment added: "Error in dashboard"
   https://bugs.launchpad.net/bugs/1425571/+attachment/4327259/+files/virt_type_fail.png

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https://bugs.launchpad.net/bugs/1425571

Title:
  Unhelpful error message and log when virt_type is incorrect in
  nova.conf

Status in OpenStack Compute (Nova):
  New

Bug description:
  I came across this issue for a simple typo in virt_type parameter in
  the file nova-compute.conf (same results if the parameter is defined
  in nova.conf) where I wrote:

  [libvirt]
  virt_type = quemu

  instead of "qemu".

  In the Horizon dashboard this lead to an error with explanation
  "Failure to prepping block device" (see image in attach), not only
  useless, but misleading since I thought about a problem with cinder.

  Also the log file nova-compute.log was not so clear (see text file in
  attach): once again "Failure prepping block device" with the addition
  of this info: "NovaException: Unable to determine disk prefix for
  None".

  Only analyzing the python code of the file in the traceback of the log
  (nova/compute/manager.py, nova/virt/libvirt/driver.py,
  nova/virt/libvirt/blockinfo.py) I could understand that the disk
  prefix (i.e. vd/hs/sd) is indeed bound to CONF.libvirt.virt_type (i.e.
  virt_type parameter in nova.conf).

  Configuration files can be modified by operators and I don't think
  they should have to look at the code to get a clue of what is going
  on, especially for an error that can be simply (at least this is my
  first impression) caught and tracked.

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