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DEVICE state was introduced back in 2017: https://lore.kernel.org/qemu-devel/20171020090556.18631-1-dgilbert@redhat.com/ Quote from Dave's cover letter, when the pre-switchover phase was enabled, the state transition looks like this: The precopy flow is: active->pre-switchover->device->completed The postcopy flow is: active->pre-switchover->postcopy-active->completed To supplement above, when the cap is not enabled: The precopy flow is: active->completed The postcopy flow is: active->postcopy-active->completed It works for us, though we have some code just to special case these state transitions, so the DEVICE state currently is special only to precopy, and only conditionally. I had a quick discussion with Libvirt developers, it turns out that this may not be necessary. IOW, it seems okay we can have DEVICE state to be generic, so that we don't have over-complicated state machines. It not only helps align all the migration state machine, help cleanup the code path especially on pre-switchover handling (see the patch itself), another side benefit is we can unconditionally have a specific state to mark the switchover phase, which might be helpful for debugging too. This patch makes the DEVICE state to be present always, marking that source QEMU is switching over. Then the state machine will be always as simple as: active-> [pre-switchover->] -> device -> [postcopy-active->] -> complete After the change, no matter whether pre-switchover or postcopy is enabled or not, we always have DEVICE state showing the switchover phase. When pre-switchover enabled, we'll have an extra stage before that. When postcopy is enabled, we'll have an extra stage after that. A few qtests need touch up in QEMU tree for this change: - A few iotest outputs (194, 203, 234, 262, 280) - Teach libqos's migrate() on "device" state Cc: Jiri Denemark <jdenemar@redhat.com> Cc: Daniel P. Berrangé <berrange@redhat.com> Cc: Dr. David Alan Gilbert <dave@treblig.org> Signed-off-by: Peter Xu <peterx@redhat.com> Tested-by: Jiri Denemark <jdenemar@redhat.com> Reviewed-by: Juraj Marcin <jmarcin@redhat.com> Link: https://lore.kernel.org/r/20250114230746.3268797-15-peterx@redhat.com Signed-off-by: Fabiano Rosas <farosas@suse.de>
49 lines
2.4 KiB
Text
49 lines
2.4 KiB
Text
=== Launch VM ===
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Enabling migration QMP events on VM...
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{"return": {}}
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=== Migrate to file ===
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{"execute": "migrate", "arguments": {"uri": "exec:cat > /dev/null"}}
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{"return": {}}
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{"data": {"status": "setup"}, "event": "MIGRATION", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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{"data": {"status": "active"}, "event": "MIGRATION", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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{"data": {"status": "device"}, "event": "MIGRATION", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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{"data": {"status": "completed"}, "event": "MIGRATION", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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VM is now stopped:
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completed
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{"execute": "query-status", "arguments": {}}
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{"return": {"running": false, "status": "postmigrate"}}
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=== Create a snapshot of the disk image ===
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{"execute": "blockdev-create", "arguments": {"job-id": "job0", "options": {"driver": "file", "filename": "TEST_DIR/PID-top", "size": 0}}}
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{"return": {}}
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{"execute": "job-dismiss", "arguments": {"id": "job0"}}
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{"return": {}}
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{"execute": "blockdev-add", "arguments": {"driver": "file", "filename": "TEST_DIR/PID-top", "node-name": "top-file"}}
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{"return": {}}
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{"execute": "blockdev-create", "arguments": {"job-id": "job0", "options": {"driver": "qcow2", "file": "top-file", "size": 1048576}}}
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{"return": {}}
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{"execute": "job-dismiss", "arguments": {"id": "job0"}}
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{"return": {}}
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{"execute": "blockdev-add", "arguments": {"driver": "qcow2", "file": "top-file", "node-name": "top-fmt"}}
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{"return": {}}
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{"execute": "blockdev-snapshot", "arguments": {"node": "base-fmt", "overlay": "top-fmt"}}
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{"return": {}}
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=== Resume the VM and simulate a write request ===
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{"execute": "cont", "arguments": {}}
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{"return": {}}
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{"return": ""}
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=== Commit it to the backing file ===
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{"execute": "block-commit", "arguments": {"auto-dismiss": false, "device": "top-fmt", "job-id": "job0", "top-node": "top-fmt"}}
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{"return": {}}
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{"execute": "job-complete", "arguments": {"id": "job0"}}
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{"return": {}}
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{"data": {"device": "job0", "len": 65536, "offset": 65536, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_READY", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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{"data": {"device": "job0", "len": 65536, "offset": 65536, "speed": 0, "type": "commit"}, "event": "BLOCK_JOB_COMPLETED", "timestamp": {"microseconds": "USECS", "seconds": "SECS"}}
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{"execute": "job-dismiss", "arguments": {"id": "job0"}}
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{"return": {}}
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