Sure, I added that the simplified test is just the user check after fresh 
install.
I can only do as fast as possible - not direct effect to the point release by 
me.
I can ask a few other people thou to advise on it after I put it into the queue.

And thanks for the paperwork on the SRU - if the requester does that it
puts some extra weight by confirming it is not just something I want :-)

Reviewing the change now (but I don't expect major surprises).

** Description changed:

  [Impact]
  
   * Users performing live migration of guests with image files
     shared over NFS between the source and target host systems
     may experience I/O errors in the guests if user id of the
     libvirt-qemu user differs between the host systems, due to
     permission errors when accessing the image files.
  
   * The 16.04 LTS is an important stream for KVM (at least on
     Power), and guest live migration over NFS is an important
     feature on it.
  
   * The proposed fix (a minimal backport from what is applied
     on Zesty/Debian, so to be very conservative for the LTS)
     simply tries to use the reserved uid for the libvirt-qemu
     user on new installations (when the user is created) if
     the reserved uid is not taken by another user (no failures
     occur if the libvirt-qemu user already exists or the uid
     is taken.)
  
  [Test Case]
  
   * Setup 2x systems with Ubuntu 16.04 LTS as KVM hosts (e.g., micro and tiny)
     (check whether the libvirt-qemu uid differs between them;
      e.g. # id libvirt-qemu )
  
   * Create a guest in the source KVM host system (e.g, microg5)
  
   * Live migrate the guest to the destination KVM host system (e.g.,
  tiny)
  
     root@micro:~# virsh migrate --live --domain microg5 qemu+ssh://tiny/system
                   --verbose --undefinesource --persistent --timeout 60
     Migration: [100 %]
  
   * Check whether the guest is now listed in the destination KVM host
  system:
  
      root@tiny:~# virsh list --all
      Id Name State
  
      12 microg5 running
  
   * Check whether I/O errors are seen in that guest:
  
      root@microg5:~# dmesg
      ...
      [ 60.818955] blk_update_request: I/O error, dev vdc, sector 96749232
      [ 60.819113] Aborting journal on device vdc2-8.
      [ 60.820121] blk_update_request: I/O error, dev vdc, sector 9084320
      [ 60.820643] EXT4-fs warning (device vdc2): ext4_end_bio:329: I/O error
                   -5 writing to inode 393279 (offset 0 size 0 ...
  
+ * Simplified test of the wanted effect:
+   - install libvirt on a system that didn't have it before and check the  
+     id of libvirt-qemu
+       $ id libvirt-qemu
+ 
  [Regression Potential]
  
   * On installations in which the libvirt-qemu user does not exist
     (e.g., first time installation of libvirt-bin) its assigned uid
     might be different from what the user previously expected, since
     now it's assigned a number from the reserved range.
  
   * Overall, the fix is very conservative (the uid assignment only
     happens in case: 1) the libvirt-qemu user is being created, and
     2) if the desired uid is not taken by another user, e.g. LDAP).
  
  [Other Info]
  
   * None at this time.
  
  <...>
  
  Please see comment #8 for the problem description, and summary of
  originally bridged comments in the description in later comments.
  
  Sorry about the inconvenience.
  
  <...>

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https://bugs.launchpad.net/bugs/1637601

Title:
  UbuntuKVM: migration using NFS mount fails #190

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