On Fri, Aug 24, 2018 at 14:40:08 -0600, Jim Fehlig wrote:

While investigating a bug [1] found by Xen's osstest I realized I don't quite understand how to handle modify jobs (e.g. BeginJob/EndJob) on virDomainObj across the various phases of V3 migration protocol. E.g. on the src host the Begin, Perform, and Confirm phases are performed. Should a modify job start (BeginJob) in the Begin phase and stop (EndJob) in the Confirm phase? Or should each phase, if necessary, do BeginJob/EndJob? Same question for dst host. IMO the job should be held across the phases on each host, preventing any modifications during the overall migration process.

Right, the first phase (Begin on the source and Prepare on the destination) should acquire the job and it should be held until the end of the migration (Confirm/Finish) to make sure nothing changes during the migration. In QEMU driver, we have several helpers around the generic job APIs: qemuMigrationJobStart - used at the beginning of migration qemuMigrationJobSetPhase - called at the beginning of each migration phase except the first one (the first one calls qemuMigrationJobStart) qemuMigrationJobContinue - called at the end of each phase except for the last one (which calls qemuMigrationJobFinish) qemuMigrationJobFinish - called at the end of migration

Although I do worry about orphaned jobs, e.g. a missed EndJob caused by some obscure error in the migration machinery.

Well, this could happen even if the job was acquired by each step separately. I don't think that spanning the job over several APIs makes the situation significantly worse. Jirka