[Qemu-devel] [Bug 1120383] Re: incremental live block migration of qemu 1.3.1 doesn't work

[Reno Gan]

Another thing i want to mention about live block migration, though i
don't know if this is really an issue of qemu or downstream libvirt.

When I was testing live migration of qemu-kvm-1.2.0 for long run, i
found a problem that block data are not completed transferred to target
host.  I traced that and found block migration thinks migration is
completed when "block_mig_state.submitted == 0",  but actually in some
cases, data are not really transferred yet.

I think the reasonable judgement for whether block migration is
completed is "block_mig_state.submitted == 0 &&
block_mig_state.read_done == 0", that is all data have been transferred.

I don't see anything about this in block-migration-fixes-for-1.4. Maybe
it has been addressed somewhere else, but if it is not, please consider
this issue and make sure data is integrated during block migration.

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https://bugs.launchpad.net/bugs/1120383

Title:
  incremental live block migration of qemu 1.3.1 doesn't work

Status in QEMU:
  New

Bug description:
  We tested qemu 1.3.1 for live migration of block device. It failed
  with error.   Since qemu-kvm 1.2.0 is ok for this test, we think this
  problem is introduced by new qemu 1.3.x releases.

  To reproduce:

  1. compile qemu 1.3.1:
      # cd qemu-1.3.1
      # ./configure --prefix=/usr --sysconfdir=/etc --target-list=x86_64-softmmu
      # make; make install

  2. prepare source(172.16.1.13):
      # qemu-img create -f qcow2 os.img -b /home/reno/wheezyx64     ###Note: 
wheezyx64 is a template image for Debian Wheezy 
      # qemu-system-x86_64 -hda os.img -m 512 --enable-kvm -vnc :51 -monitor 
stdio

  3. prepare destination(172.16.1.14):
      # qemu-img create -f qcow2 os.img -b /home/reno/wheezyx64    
      # qemu-system-x86_64 -hda os.img -m 512 --enable-kvm -vnc :51 -incoming 
tcp:0:4444

  4. do live migrate:
      on source monitor command prompt, input:
      (qemu) migrate -i tcp:172.16.1.14:4444

  monitor command will quit immediately and on destination host, there are 
errors thrown:
      Receiving block device images
      Co-routine re-entered recursively
      Aborted

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