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| -rw-r--r-- | docs/interop/live-block-operations.rst | 50 | ||||
| -rw-r--r-- | qapi/block-core.json | 6 |
2 files changed, 38 insertions, 18 deletions
diff --git a/docs/interop/live-block-operations.rst b/docs/interop/live-block-operations.rst index 5f01797..734252b 100644 --- a/docs/interop/live-block-operations.rst +++ b/docs/interop/live-block-operations.rst @@ -506,26 +506,40 @@ Again, given our familiar disk image chain:: [A] <-- [B] <-- [C] <-- [D] -The ``drive-mirror`` (and its newer equivalent ``blockdev-mirror``) allows -you to copy data from the entire chain into a single target image (which -can be located on a different host). - -Once a 'mirror' job has started, there are two possible actions while a -``drive-mirror`` job is active: - -(1) Issuing the command ``block-job-cancel`` after it emits the event - ``BLOCK_JOB_CANCELLED``: will (after completing synchronization of - the content from the disk image chain to the target image, [E]) - create a point-in-time (which is at the time of *triggering* the - cancel command) copy, contained in image [E], of the the entire disk +The ``drive-mirror`` (and its newer equivalent ``blockdev-mirror``) +allows you to copy data from the entire chain into a single target image +(which can be located on a different host), [E]. + +.. note:: + + When you cancel an in-progress 'mirror' job *before* the source and + target are synchronized, ``block-job-cancel`` will emit the event + ``BLOCK_JOB_CANCELLED``. However, note that if you cancel a + 'mirror' job *after* it has indicated (via the event + ``BLOCK_JOB_READY``) that the source and target have reached + synchronization, then the event emitted by ``block-job-cancel`` + changes to ``BLOCK_JOB_COMPLETED``. + + Besides the 'mirror' job, the "active ``block-commit``" is the only + other block device job that emits the event ``BLOCK_JOB_READY``. + The rest of the block device jobs ('stream', "non-active + ``block-commit``", and 'backup') end automatically. + +So there are two possible actions to take, after a 'mirror' job has +emitted the event ``BLOCK_JOB_READY``, indicating that the source and +target have reached synchronization: + +(1) Issuing the command ``block-job-cancel`` (after it emits the event + ``BLOCK_JOB_COMPLETED``) will create a point-in-time (which is at + the time of *triggering* the cancel command) copy of the entire disk image chain (or only the top-most image, depending on the ``sync`` - mode). + mode), contained in the target image [E]. One use case for this is + live VM migration with non-shared storage. -(2) Issuing the command ``block-job-complete`` after it emits the event - ``BLOCK_JOB_COMPLETED``: will, after completing synchronization of - the content, adjust the guest device (i.e. live QEMU) to point to - the target image, and, causing all the new writes from this point on - to happen there. One use case for this is live storage migration. +(2) Issuing the command ``block-job-complete`` (after it emits the event + ``BLOCK_JOB_COMPLETED``) will adjust the guest device (i.e. live + QEMU) to point to the target image, [E], causing all the new writes + from this point on to happen there. About synchronization modes: The synchronization mode determines *which* part of the disk image chain will be copied to the target. diff --git a/qapi/block-core.json b/qapi/block-core.json index 76bf50f..dd763dc 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -2065,6 +2065,12 @@ # BLOCK_JOB_CANCELLED event. Before that happens the job is still visible when # enumerated using query-block-jobs. # +# Note that if you issue 'block-job-cancel' after 'drive-mirror' has indicated +# (via the event BLOCK_JOB_READY) that the source and destination are +# synchronized, then the event triggered by this command changes to +# BLOCK_JOB_COMPLETED, to indicate that the mirroring has ended and the +# destination now has a point-in-time copy tied to the time of the cancellation. +# # For streaming, the image file retains its backing file unless the streaming # operation happens to complete just as it is being cancelled. A new streaming # operation can be started at a later time to finish copying all data from the |