| Message ID | 20171117162536.23225-1-kchamart@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 11/17/2017 10:25 AM, Kashyap Chamarthy wrote: > When you cancel an in-progress live block operation with QMP > `block-job-cancel`, it emits the event: BLOCK_JOB_CANCELLED. However, > when `block-job-cancel` is issued after `drive-mirror` has indicated (by > emitting the event BLOCK_JOB_READY) that the source and destination > remain synchronized: > > But this is expected behaviour, where the _COMPLETED event indicates > that synchronization has successfully ended (and the destination has a > point-in-time copy, which is at the time of cancel). > > So add a small note to this effect in 'block-core.json'. While at it, > also update the "Live disk synchronization -- drive-mirror and > blockdev-mirror" section in 'live-block-operations.rst'. > > (Thanks: Max Reitz for reminding me of this caveat on IRC.) Sorry for not wordsmithing on earlier versions: > > Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> > --- > +.. 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 (by emitting the event > + ``BLOCK_JOB_READY``) that the source and target now remain > + synchronized, then ``block-job-cancel`` will emit the event Might read slightly nicer as: the source and target have reached synchronization, > +++ b/qapi/block-core.json > @@ -2065,6 +2065,14 @@ > # BLOCK_JOB_CANCELLED event. Before that happens the job is still visible when > # enumerated using query-block-jobs. > # > +# Note that the 'block-job-cancel' command will emit the event > +# BLOCK_JOB_COMPLETED if you issue it ('block-job-cancel') after 'drive-mirror' > +# has indicated (by emitting the event BLOCK_JOB_READY) that the source and > +# destination remain synchronized. In this case, the BLOCK_JOB_COMPLETED > +# event indicates that synchronization (from 'drive-mirror') has successfully > +# ended and the destination now has a point-in-time copy, which is at the time > +# of cancel. Accurate, but a bit hard to follow the flow of the sentence. Might read nicer as: 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. Documentation is worth of inclusion in 2.11. Whether you keep your wording, or incorporate mine in a v4, you can add: Reviewed-by: Eric Blake <eblake@redhat.com>
On Fri, Nov 17, 2017 at 11:07:41AM -0600, Eric Blake wrote: > On 11/17/2017 10:25 AM, Kashyap Chamarthy wrote: [...] > Sorry for not wordsmithing on earlier versions: That's fine. Always appreciate your wordsmithing :-) > > + 'mirror' job *after* it has indicated (by emitting the event > > + ``BLOCK_JOB_READY``) that the source and target now remain > > + synchronized, then ``block-job-cancel`` will emit the event > > Might read slightly nicer as: > > the source and target have reached synchronization, Ah, that sounds nicer indeed. Will fix. [...] > > +# Note that the 'block-job-cancel' command will emit the event > > +# BLOCK_JOB_COMPLETED if you issue it ('block-job-cancel') after 'drive-mirror' > > +# has indicated (by emitting the event BLOCK_JOB_READY) that the source and > > +# destination remain synchronized. In this case, the BLOCK_JOB_COMPLETED > > +# event indicates that synchronization (from 'drive-mirror') has successfully > > +# ended and the destination now has a point-in-time copy, which is at the time > > +# of cancel. > > > Accurate, but a bit hard to follow the flow of the sentence. Yeah, I wasn't satisfied with my phrasing too. I sat on it for nearly half an hour, and still it came out super clunky. > Might read nicer as: > > 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. Thanks, yours reads much nicer. > Documentation is worth of inclusion in 2.11. Whether you keep your > wording, or incorporate mine in a v4, you can add: > Reviewed-by: Eric Blake <eblake@redhat.com> I'll definitely incorporate in v4. I'll also make similar wording adjustment in live-block-operations.rst. Thanks for the quick review.
diff --git a/docs/interop/live-block-operations.rst b/docs/interop/live-block-operations.rst index 5f01797..3cb64f6 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 (by emitting the event + ``BLOCK_JOB_READY``) that the source and target now remain + synchronized, then ``block-job-cancel`` will emit the event + ``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, after a 'mirror' job has +emitted the event ``BLOCK_JOB_READY``, indicating that source and target +now remain synchronized: + +(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]. -(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. One use case for this is live + storage migration. 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 ab96e34..4ecfd1f 100644 --- a/qapi/block-core.json +++ b/qapi/block-core.json @@ -2065,6 +2065,14 @@ # BLOCK_JOB_CANCELLED event. Before that happens the job is still visible when # enumerated using query-block-jobs. # +# Note that the 'block-job-cancel' command will emit the event +# BLOCK_JOB_COMPLETED if you issue it ('block-job-cancel') after 'drive-mirror' +# has indicated (by emitting the event BLOCK_JOB_READY) that the source and +# destination remain synchronized. In this case, the BLOCK_JOB_COMPLETED +# event indicates that synchronization (from 'drive-mirror') has successfully +# ended and the destination now has a point-in-time copy, which is at the time +# of cancel. +# # 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
When you cancel an in-progress live block operation with QMP `block-job-cancel`, it emits the event: BLOCK_JOB_CANCELLED. However, when `block-job-cancel` is issued after `drive-mirror` has indicated (by emitting the event BLOCK_JOB_READY) that the source and destination remain synchronized: [...] # Snip `drive-mirror` invocation & outputs { "execute":"block-job-cancel", "arguments":{ "device":"virtio0" } } {"return": {}} It (`block-job-cancel`) will counterintuitively emit the event 'BLOCK_JOB_COMPLETED': { "timestamp":{ "seconds":1510678024, "microseconds":526240 }, "event":"BLOCK_JOB_COMPLETED", "data":{ "device":"virtio0", "len":41126400, "offset":41126400, "speed":0, "type":"mirror" } } But this is expected behaviour, where the _COMPLETED event indicates that synchronization has successfully ended (and the destination has a point-in-time copy, which is at the time of cancel). So add a small note to this effect in 'block-core.json'. While at it, also update the "Live disk synchronization -- drive-mirror and blockdev-mirror" section in 'live-block-operations.rst'. (Thanks: Max Reitz for reminding me of this caveat on IRC.) Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com> --- Changes in v3: - Fix / rewrite the section "Live disk synchronization -- drive-mirror and blockdev-mirror" to note this gotcha [John Snow] Changes in v2: - "Note:" seems to be a special construct in Patchew, my usage caused a build failure. So do: s/Note:/Note that/ - Add the missing 'Signed-off-by' --- docs/interop/live-block-operations.rst | 50 ++++++++++++++++++++++------------ qapi/block-core.json | 8 ++++++ 2 files changed, 40 insertions(+), 18 deletions(-)