Kevin Wolf <kw...@redhat.com> writes: > Am 19.11.2019 um 11:54 hat Sergio Lopez geschrieben: >> >> Max Reitz <mre...@redhat.com> writes: >> >> > On 13.11.19 14:24, Sergio Lopez wrote: >> >> >> >> Sergio Lopez <s...@redhat.com> writes: >> >> >> >>> no-re...@patchew.org writes: >> >>> >> >>>> Patchew URL: >> >>>> https://patchew.org/QEMU/20191112113012.71136-1-...@redhat.com/ >> >>>> >> >>>> >> >>>> >> >>>> Hi, >> >>>> >> >>>> This series failed the docker-quick@centos7 build test. Please find the >> >>>> testing commands and >> >>>> their output below. If you have Docker installed, you can probably >> >>>> reproduce it >> >>>> locally. >> >>>> >> >>>> === TEST SCRIPT BEGIN === >> >>>> #!/bin/bash >> >>>> make docker-image-centos7 V=1 NETWORK=1 >> >>>> time make docker-test-quick@centos7 SHOW_ENV=1 J=14 NETWORK=1 >> >>>> === TEST SCRIPT END === >> >>>> >> >>>> TEST iotest-qcow2: 268 >> >>>> Failures: 141 >> >>> >> >>> Hm... 141 didn't fail in my test machine. I'm going to have a look. >> >> >> >> So here's the output: >> >> >> >> --- /root/qemu/tests/qemu-iotests/141.out 2019-11-12 04:43:27.651557587 >> >> -0500 >> >> +++ /root/qemu/build/tests/qemu-iotests/141.out.bad 2019-11-13 >> >> 08:12:06.575967337 -0500 >> >> @@ -10,6 +10,8 @@ >> >> Formatting 'TEST_DIR/o.IMGFMT', fmt=IMGFMT size=1048576 >> >> backing_file=TEST_DIR/t.IMGFMT backing_fmt=IMGFMT >> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, >> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "created", "id": "job0"}} >> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, >> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}} >> >> +{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, >> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "paused", "id": "job0"}} >> >> +{"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, >> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "running", "id": "job0"}} >> >> {"error": {"class": "GenericError", "desc": "Node 'drv0' is busy: node >> >> is used as backing hd of 'NODE_NAME'"}} >> >> {"return": {}} >> >> {"timestamp": {"seconds": TIMESTAMP, "microseconds": TIMESTAMP}, >> >> "event": "JOB_STATUS_CHANGE", "data": {"status": "aborting", "id": >> >> "job0"}} >> >> >> >> Those extra lines, the "paused" and "running", are a result of the job >> >> being done in a transaction, within a drained section. >> >> >> >> We can update 141.out, but now I'm wondering, was it safe creating the >> >> job at do_drive_backup() outside of a drained section, as >> >> qmp_drive_backup was doing? >> > >> > I think it is. Someone needs to drain the source node before attaching >> > the job filter (which intercepts writes), and bdrv_backup_top_append() >> > does precisely this. >> > >> > If the source node is in an I/O thread, you could argue that the drain >> > starts later than when the user has invoked the backup command, and so >> > some writes might slip through. That’s correct. But at the same time, >> > it’s impossible to drain it the instant the command is received. So >> > some writes might always slip through (and the drain will not stop them >> > either, it will just let them happen). >> > >> > Therefore, I think it’s fine the way it is. >> > >> >> Do you think there may be any potential drawbacks as a result of always >> >> doing it now inside a drained section? >> > >> > Well, one drawback is clearly visible. The job goes to paused for no >> > reason. >> >> This is something that already happens when requesting the drive-backup >> through a transaction: >> >> {"execute":"transaction","arguments":{"actions":[{"type":"drive-backup","data":{"device":"drv0","target":"o.qcow2","sync":"full","format":"qcow2"}}]}} >> >> I don't think it makes sense to have two different behaviors for the >> same action. So we either accept the additional pause+resume iteration >> for qmp_drive_backup, or we remove the drained section from the >> transaction based one. >> >> What do you think? > > Draining all involved nodes is necessary for transactions, because you > want a consistent backup across all involved disks. That is, you want it > to be a snapshot at the same point in time for all of them - no requests > may happen between starting backup on the first and the second disk. > > For a single device operation, this requirement doesn't exist, because > there is nothing else that must happen at the same point in time.
This poses a problem with the unification strategy you suggested for qmp commands and transactions. I guess that, if we really want to preserve the original behavior, we can extend DriveBackup to add a flag to indicate whether the transaction should create a drained section or not. Does this sound reasonable to you? Thanks, Sergio.
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