mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-11-05 12:51:12 +00:00
106 lines
3.3 KiB
ReStructuredText
106 lines
3.3 KiB
ReStructuredText
QEMU Migration Phases
|
|
=====================
|
|
|
|
.. contents::
|
|
|
|
QEMU supports only migration protocols 2 and 3 (1 was lacking too many
|
|
steps). Repeating the protocol sequences from libvirt.c:
|
|
|
|
Migration protocol v2 API Sequence
|
|
----------------------------------
|
|
|
|
**Src**: ``DumpXML``
|
|
- Generate XML to pass to dst
|
|
|
|
**Dst**: ``Prepare``
|
|
- Get ready to accept incoming VM
|
|
- Generate optional cookie to pass to src
|
|
|
|
**Src**: ``Perform``
|
|
- Start migration and wait for send completion
|
|
- Kill off VM if successful, resume if failed
|
|
|
|
**Dst**: ``Finish``
|
|
- Wait for recv completion and check status
|
|
- Kill off VM if unsuccessful
|
|
|
|
Migration protocol v3 API Sequence
|
|
----------------------------------
|
|
|
|
**Src**: ``Begin``
|
|
- Generate XML to pass to dst
|
|
- Generate optional cookie to pass to dst
|
|
|
|
**Dst**: ``Prepare``
|
|
- Get ready to accept incoming VM
|
|
- Generate optional cookie to pass to src
|
|
|
|
**Src**: ``Perform``
|
|
- Start migration and wait for send completion
|
|
- Generate optional cookie to pass to dst
|
|
|
|
**Dst**: ``Finish``
|
|
- Wait for recv completion and check status
|
|
- Kill off VM if failed, resume if success
|
|
- Generate optional cookie to pass to src
|
|
|
|
**Src**: ``Confirm``
|
|
- Kill off VM if success, resume if failed
|
|
|
|
QEMU Migration Locking Rules
|
|
============================
|
|
|
|
Migration is a complicated beast which may span across several APIs on both
|
|
source and destination side and we need to keep the domain we are migrating in
|
|
a consistent state during the whole process.
|
|
|
|
To avoid anyone from changing the domain in the middle of migration we need to
|
|
keep ``MIGRATION_OUT`` job active during migration from ``Begin`` to
|
|
``Confirm`` on the source side and ``MIGRATION_IN`` job has to be active from
|
|
``Prepare`` to ``Finish`` on the destination side.
|
|
|
|
For this purpose we introduce several helper methods to deal with locking
|
|
primitives (described in `qemu-threads <qemu-threads.html>`__) in the right way:
|
|
|
|
* ``qemuMigrationJobStart``
|
|
|
|
* ``qemuMigrationJobContinue``
|
|
|
|
* ``qemuMigrationJobStartPhase``
|
|
|
|
* ``qemuMigrationJobSetPhase``
|
|
|
|
* ``qemuMigrationJobFinish``
|
|
|
|
The sequence of calling ``qemuMigrationJob*`` helper methods is as follows:
|
|
|
|
- The first API of a migration protocol (``Prepare`` or ``Perform/Begin``
|
|
depending on migration type and version) has to start migration job and keep
|
|
it active::
|
|
|
|
qemuMigrationJobStart(driver, vm, VIR_JOB_MIGRATION_{IN,OUT});
|
|
qemuMigrationJobSetPhase(vm, QEMU_MIGRATION_PHASE_*);
|
|
...do work...
|
|
qemuMigrationJobContinue(vm);
|
|
|
|
- All consequent phases except for the last one have to keep the job active::
|
|
|
|
if (!qemuMigrationJobIsActive(vm, VIR_JOB_MIGRATION_{IN,OUT}))
|
|
return;
|
|
qemuMigrationJobStartPhase(driver, vm, QEMU_MIGRATION_PHASE_*);
|
|
...do work...
|
|
qemuMigrationJobContinue(vm);
|
|
|
|
- The last migration phase finally finishes the migration job::
|
|
|
|
if (!qemuMigrationJobIsActive(vm, VIR_JOB_MIGRATION_{IN,OUT}))
|
|
return;
|
|
qemuMigrationJobStartPhase(driver, vm, QEMU_MIGRATION_PHASE_*);
|
|
...do work...
|
|
qemuMigrationJobFinish(vm);
|
|
|
|
While migration job is running (i.e., after ``qemuMigrationJobStart*`` but before
|
|
``qemuMigrationJob{Continue,Finish}``), migration phase can be advanced using::
|
|
|
|
qemuMigrationJobSetPhase(vm, QEMU_MIGRATION_PHASE_*);
|