5fcbeb0681
With the experimental x-nbd-server-add-bitmap command, there was a window of time where an NBD client could see the export but not the associated dirty bitmap, which can cause a client that planned on using the dirty bitmap to be forced to treat the entire image as dirty as a safety fallback. Furthermore, if the QMP client successfully exports a disk but then fails to add the bitmap, it has to take on the burden of removing the export. Since we don't allow changing the exposed dirty bitmap (whether to a different bitmap, or removing advertisement of the bitmap), it is nicer to make the bitmap tied to the export at the time the export is created, with automatic failure to export if the bitmap is not available. The experimental command included an optional 'bitmap-export-name' field for remapping the name exposed over NBD to be different from the bitmap name stored on disk. However, my libvirt demo code for implementing differential backups on top of persistent bitmaps did not need to take advantage of that feature (it is instead possible to create a new temporary bitmap with the desired name, use block-dirty-bitmap-merge to merge one or more persistent bitmaps into the temporary, then associate the temporary with the NBD export, if control is needed over the exported bitmap name). Hence, I'm not copying that part of the experiment over to the stable addition. For more details on the libvirt demo, see https://www.redhat.com/archives/libvir-list/2018-October/msg01254.html, https://kvmforum2018.sched.com/event/FzuB/facilitating-incremental-backup-eric-blake-red-hat This patch focuses on the user interface, and reduces (but does not completely eliminate) the window where an NBD client can see the export but not the dirty bitmap, with less work to clean up after errors. Later patches will add further cleanups now that this interface is declared stable via a single QMP command, including removing the race window. Update test 223 to use the new interface. Signed-off-by: Eric Blake <eblake@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20190111194720.15671-6-eblake@redhat.com>
73 lines
2.8 KiB
Plaintext
73 lines
2.8 KiB
Plaintext
QA output created by 223
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=== Create partially sparse image, then add dirty bitmaps ===
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=4194304
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wrote 2097152/2097152 bytes at offset 1048576
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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Testing:
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QMP_VERSION
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, "event": "SHUTDOWN", "data": {"guest": false, "reason": "host-qmp-quit"}}
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=== Write part of the file under active bitmap ===
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wrote 512/512 bytes at offset 512
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512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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wrote 2097152/2097152 bytes at offset 2097152
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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=== End dirty bitmaps, and start serving image over NBD ===
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{"return": {}}
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{"return": {}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server not running"}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server already running"}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "Cannot find device=nosuch nor node_name=nosuch"}}
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{"error": {"class": "GenericError", "desc": "NBD server already has export named 'n'"}}
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{"error": {"class": "GenericError", "desc": "Enabled bitmap 'b2' incompatible with readonly export"}}
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{"error": {"class": "GenericError", "desc": "Bitmap 'b3' is not found"}}
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{"return": {}}
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=== Contrast normal status to large granularity dirty-bitmap ===
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read 512/512 bytes at offset 512
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512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 524288/524288 bytes at offset 524288
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512 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 1048576/1048576 bytes at offset 1048576
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1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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read 2097152/2097152 bytes at offset 2097152
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2 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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[{ "start": 0, "length": 4096, "depth": 0, "zero": false, "data": true},
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{ "start": 4096, "length": 1044480, "depth": 0, "zero": true, "data": false},
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{ "start": 1048576, "length": 3145728, "depth": 0, "zero": false, "data": true}]
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[{ "start": 0, "length": 65536, "depth": 0, "zero": false, "data": false},
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{ "start": 65536, "length": 2031616, "depth": 0, "zero": false, "data": true},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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=== Contrast to small granularity dirty-bitmap ===
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[{ "start": 0, "length": 512, "depth": 0, "zero": false, "data": true},
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{ "start": 512, "length": 512, "depth": 0, "zero": false, "data": false},
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{ "start": 1024, "length": 2096128, "depth": 0, "zero": false, "data": true},
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{ "start": 2097152, "length": 2097152, "depth": 0, "zero": false, "data": false}]
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=== End NBD server ===
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{"return": {}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "Export 'n2' is not found"}}
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{"return": {}}
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{"error": {"class": "GenericError", "desc": "NBD server not running"}}
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{"return": {}}
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*** done
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