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[Qemu-devel] [PATCH v7 1/2] bitmaps.md: Convert to rST; move it into 'in
|
From: |
Kashyap Chamarthy |
|
Subject: |
[Qemu-devel] [PATCH v7 1/2] bitmaps.md: Convert to rST; move it into 'interop' dir |
|
Date: |
Mon, 17 Jul 2017 12:52:04 +0200 |
This is part of the on-going effort to convert QEMU upstream
documentation syntax to reStructuredText (rST).
The conversion to rST was done using:
$ pandoc -f markdown -t rst bitmaps.md -o bitmaps.rst
Then, make a couple of small syntactical adjustments. While at it,
reword a statement to avoid ambiguity. Addressing the feedback from
this thread:
https://lists.nongnu.org/archive/html/qemu-devel/2017-06/msg05428.html
Signed-off-by: Kashyap Chamarthy <address@hidden>
Reviewed-by: John Snow <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
---
* A Sphinx-rendered HTML version is here:
https://kashyapc.fedorapeople.org/v7-QEMU-Docs/_build/html/docs/bitmaps.html
* v7
- Fix two minor (pre-existing) typos pointed out by Eric Blake here:
https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg02511.html
- Carry Eric's 'Reviewed-by'
* v6 -- No change; just carry the 'Reviewed-by' from John Snow.
* v5 -- No change; just carry the 'Reviewed-by' from John Snow.
* For v4: the patch had "v4" subject prefix because I rolled this in
along with the other document (live-block-operations.rst) that is in
review, which was actually at v4.
---
docs/devel/bitmaps.md | 505 ------------------------------------------
docs/interop/bitmaps.rst | 555 +++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 555 insertions(+), 505 deletions(-)
delete mode 100644 docs/devel/bitmaps.md
create mode 100644 docs/interop/bitmaps.rst
diff --git a/docs/devel/bitmaps.md b/docs/devel/bitmaps.md
deleted file mode 100644
index a2e8d51..0000000
--- a/docs/devel/bitmaps.md
+++ /dev/null
@@ -1,505 +0,0 @@
-<!--
-Copyright 2015 John Snow <address@hidden> and Red Hat, Inc.
-All rights reserved.
-
-This file is licensed via The FreeBSD Documentation License, the full text of
-which is included at the end of this document.
--->
-
-# Dirty Bitmaps and Incremental Backup
-
-* Dirty Bitmaps are objects that track which data needs to be backed up for the
- next incremental backup.
-
-* Dirty bitmaps can be created at any time and attached to any node
- (not just complete drives.)
-
-## Dirty Bitmap Names
-
-* A dirty bitmap's name is unique to the node, but bitmaps attached to
different
- nodes can share the same name.
-
-* Dirty bitmaps created for internal use by QEMU may be anonymous and have no
- name, but any user-created bitmaps may not be. There can be any number of
- anonymous bitmaps per node.
-
-* The name of a user-created bitmap must not be empty ("").
-
-## Bitmap Modes
-
-* A Bitmap can be "frozen," which means that it is currently in-use by a backup
- operation and cannot be deleted, renamed, written to, reset,
- etc.
-
-* The normal operating mode for a bitmap is "active."
-
-## Basic QMP Usage
-
-### Supported Commands ###
-
-* block-dirty-bitmap-add
-* block-dirty-bitmap-remove
-* block-dirty-bitmap-clear
-
-### Creation
-
-* To create a new bitmap, enabled, on the drive with id=drive0:
-
-```json
-{ "execute": "block-dirty-bitmap-add",
- "arguments": {
- "node": "drive0",
- "name": "bitmap0"
- }
-}
-```
-
-* This bitmap will have a default granularity that matches the cluster size of
- its associated drive, if available, clamped to between [4KiB, 64KiB].
- The current default for qcow2 is 64KiB.
-
-* To create a new bitmap that tracks changes in 32KiB segments:
-
-```json
-{ "execute": "block-dirty-bitmap-add",
- "arguments": {
- "node": "drive0",
- "name": "bitmap0",
- "granularity": 32768
- }
-}
-```
-
-### Deletion
-
-* Bitmaps that are frozen cannot be deleted.
-
-* Deleting the bitmap does not impact any other bitmaps attached to the same
- node, nor does it affect any backups already created from this node.
-
-* Because bitmaps are only unique to the node to which they are attached,
- you must specify the node/drive name here, too.
-
-```json
-{ "execute": "block-dirty-bitmap-remove",
- "arguments": {
- "node": "drive0",
- "name": "bitmap0"
- }
-}
-```
-
-### Resetting
-
-* Resetting a bitmap will clear all information it holds.
-
-* An incremental backup created from an empty bitmap will copy no data,
- as if nothing has changed.
-
-```json
-{ "execute": "block-dirty-bitmap-clear",
- "arguments": {
- "node": "drive0",
- "name": "bitmap0"
- }
-}
-```
-
-## Transactions
-
-### Justification
-
-Bitmaps can be safely modified when the VM is paused or halted by using
-the basic QMP commands. For instance, you might perform the following actions:
-
-1. Boot the VM in a paused state.
-2. Create a full drive backup of drive0.
-3. Create a new bitmap attached to drive0.
-4. Resume execution of the VM.
-5. Incremental backups are ready to be created.
-
-At this point, the bitmap and drive backup would be correctly in sync,
-and incremental backups made from this point forward would be correctly aligned
-to the full drive backup.
-
-This is not particularly useful if we decide we want to start incremental
-backups after the VM has been running for a while, for which we will need to
-perform actions such as the following:
-
-1. Boot the VM and begin execution.
-2. Using a single transaction, perform the following operations:
- * Create bitmap0.
- * Create a full drive backup of drive0.
-3. Incremental backups are now ready to be created.
-
-### Supported Bitmap Transactions
-
-* block-dirty-bitmap-add
-* block-dirty-bitmap-clear
-
-The usages are identical to their respective QMP commands, but see below
-for examples.
-
-### Example: New Incremental Backup
-
-As outlined in the justification, perhaps we want to create a new incremental
-backup chain attached to a drive.
-
-```json
-{ "execute": "transaction",
- "arguments": {
- "actions": [
- {"type": "block-dirty-bitmap-add",
- "data": {"node": "drive0", "name": "bitmap0"} },
- {"type": "drive-backup",
- "data": {"device": "drive0", "target": "/path/to/full_backup.img",
- "sync": "full", "format": "qcow2"} }
- ]
- }
-}
-```
-
-### Example: New Incremental Backup Anchor Point
-
-Maybe we just want to create a new full backup with an existing bitmap and
-want to reset the bitmap to track the new chain.
-
-```json
-{ "execute": "transaction",
- "arguments": {
- "actions": [
- {"type": "block-dirty-bitmap-clear",
- "data": {"node": "drive0", "name": "bitmap0"} },
- {"type": "drive-backup",
- "data": {"device": "drive0", "target": "/path/to/new_full_backup.img",
- "sync": "full", "format": "qcow2"} }
- ]
- }
-}
-```
-
-## Incremental Backups
-
-The star of the show.
-
-**Nota Bene!** Only incremental backups of entire drives are supported for now.
-So despite the fact that you can attach a bitmap to any arbitrary node, they
are
-only currently useful when attached to the root node. This is because
-drive-backup only supports drives/devices instead of arbitrary nodes.
-
-### Example: First Incremental Backup
-
-1. Create a full backup and sync it to the dirty bitmap, as in the
transactional
-examples above; or with the VM offline, manually create a full copy and then
-create a new bitmap before the VM begins execution.
-
- * Let's assume the full backup is named 'full_backup.img'.
- * Let's assume the bitmap you created is 'bitmap0' attached to 'drive0'.
-
-2. Create a destination image for the incremental backup that utilizes the
-full backup as a backing image.
-
- * Let's assume it is named 'incremental.0.img'.
-
- ```sh
- # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
- ```
-
-3. Issue the incremental backup command:
-
- ```json
- { "execute": "drive-backup",
- "arguments": {
- "device": "drive0",
- "bitmap": "bitmap0",
- "target": "incremental.0.img",
- "format": "qcow2",
- "sync": "incremental",
- "mode": "existing"
- }
- }
- ```
-
-### Example: Second Incremental Backup
-
-1. Create a new destination image for the incremental backup that points to the
- previous one, e.g.: 'incremental.1.img'
-
- ```sh
- # qemu-img create -f qcow2 incremental.1.img -b incremental.0.img -F qcow2
- ```
-
-2. Issue a new incremental backup command. The only difference here is that we
- have changed the target image below.
-
- ```json
- { "execute": "drive-backup",
- "arguments": {
- "device": "drive0",
- "bitmap": "bitmap0",
- "target": "incremental.1.img",
- "format": "qcow2",
- "sync": "incremental",
- "mode": "existing"
- }
- }
- ```
-
-## Errors
-
-* In the event of an error that occurs after a backup job is successfully
- launched, either by a direct QMP command or a QMP transaction, the user
- will receive a BLOCK_JOB_COMPLETE event with a failure message, accompanied
- by a BLOCK_JOB_ERROR event.
-
-* In the case of an event being cancelled, the user will receive a
- BLOCK_JOB_CANCELLED event instead of a pair of COMPLETE and ERROR events.
-
-* In either case, the incremental backup data contained within the bitmap is
- safely rolled back, and the data within the bitmap is not lost. The image
- file created for the failed attempt can be safely deleted.
-
-* Once the underlying problem is fixed (e.g. more storage space is freed up),
- you can simply retry the incremental backup command with the same bitmap.
-
-### Example
-
-1. Create a target image:
-
- ```sh
- # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
- ```
-
-2. Attempt to create an incremental backup via QMP:
-
- ```json
- { "execute": "drive-backup",
- "arguments": {
- "device": "drive0",
- "bitmap": "bitmap0",
- "target": "incremental.0.img",
- "format": "qcow2",
- "sync": "incremental",
- "mode": "existing"
- }
- }
- ```
-
-3. Receive an event notifying us of failure:
-
- ```json
- { "timestamp": { "seconds": 1424709442, "microseconds": 844524 },
- "data": { "speed": 0, "offset": 0, "len": 67108864,
- "error": "No space left on device",
- "device": "drive1", "type": "backup" },
- "event": "BLOCK_JOB_COMPLETED" }
- ```
-
-4. Delete the failed incremental, and re-create the image.
-
- ```sh
- # rm incremental.0.img
- # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
- ```
-
-5. Retry the command after fixing the underlying problem,
- such as freeing up space on the backup volume:
-
- ```json
- { "execute": "drive-backup",
- "arguments": {
- "device": "drive0",
- "bitmap": "bitmap0",
- "target": "incremental.0.img",
- "format": "qcow2",
- "sync": "incremental",
- "mode": "existing"
- }
- }
- ```
-
-6. Receive confirmation that the job completed successfully:
-
- ```json
- { "timestamp": { "seconds": 1424709668, "microseconds": 526525 },
- "data": { "device": "drive1", "type": "backup",
- "speed": 0, "len": 67108864, "offset": 67108864},
- "event": "BLOCK_JOB_COMPLETED" }
- ```
-
-### Partial Transactional Failures
-
-* Sometimes, a transaction will succeed in launching and return success,
- but then later the backup jobs themselves may fail. It is possible that
- a management application may have to deal with a partial backup failure
- after a successful transaction.
-
-* If multiple backup jobs are specified in a single transaction, when one of
- them fails, it will not interact with the other backup jobs in any way.
-
-* The job(s) that succeeded will clear the dirty bitmap associated with the
- operation, but the job(s) that failed will not. It is not "safe" to delete
- any incremental backups that were created successfully in this scenario,
- even though others failed.
-
-#### Example
-
-* QMP example highlighting two backup jobs:
-
- ```json
- { "execute": "transaction",
- "arguments": {
- "actions": [
- { "type": "drive-backup",
- "data": { "device": "drive0", "bitmap": "bitmap0",
- "format": "qcow2", "mode": "existing",
- "sync": "incremental", "target": "d0-incr-1.qcow2" } },
- { "type": "drive-backup",
- "data": { "device": "drive1", "bitmap": "bitmap1",
- "format": "qcow2", "mode": "existing",
- "sync": "incremental", "target": "d1-incr-1.qcow2" } },
- ]
- }
- }
- ```
-
-* QMP example response, highlighting one success and one failure:
- * Acknowledgement that the Transaction was accepted and jobs were launched:
- ```json
- { "return": {} }
- ```
-
- * Later, QEMU sends notice that the first job was completed:
- ```json
- { "timestamp": { "seconds": 1447192343, "microseconds": 615698 },
- "data": { "device": "drive0", "type": "backup",
- "speed": 0, "len": 67108864, "offset": 67108864 },
- "event": "BLOCK_JOB_COMPLETED"
- }
- ```
-
- * Later yet, QEMU sends notice that the second job has failed:
- ```json
- { "timestamp": { "seconds": 1447192399, "microseconds": 683015 },
- "data": { "device": "drive1", "action": "report",
- "operation": "read" },
- "event": "BLOCK_JOB_ERROR" }
- ```
-
- ```json
- { "timestamp": { "seconds": 1447192399, "microseconds": 685853 },
- "data": { "speed": 0, "offset": 0, "len": 67108864,
- "error": "Input/output error",
- "device": "drive1", "type": "backup" },
- "event": "BLOCK_JOB_COMPLETED" }
-
-* In the above example, "d0-incr-1.qcow2" is valid and must be kept,
- but "d1-incr-1.qcow2" is invalid and should be deleted. If a VM-wide
- incremental backup of all drives at a point-in-time is to be made,
- new backups for both drives will need to be made, taking into account
- that a new incremental backup for drive0 needs to be based on top of
- "d0-incr-1.qcow2."
-
-### Grouped Completion Mode
-
-* While jobs launched by transactions normally complete or fail on their own,
- it is possible to instruct them to complete or fail together as a group.
-
-* QMP transactions take an optional properties structure that can affect
- the semantics of the transaction.
-
-* The "completion-mode" transaction property can be either "individual"
- which is the default, legacy behavior described above, or "grouped,"
- a new behavior detailed below.
-
-* Delayed Completion: In grouped completion mode, no jobs will report
- success until all jobs are ready to report success.
-
-* Grouped failure: If any job fails in grouped completion mode, all remaining
- jobs will be cancelled. Any incremental backups will restore their dirty
- bitmap objects as if no backup command was ever issued.
-
- * Regardless of if QEMU reports a particular incremental backup job as
- CANCELLED or as an ERROR, the in-memory bitmap will be restored.
-
-#### Example
-
-* Here's the same example scenario from above with the new property:
-
- ```json
- { "execute": "transaction",
- "arguments": {
- "actions": [
- { "type": "drive-backup",
- "data": { "device": "drive0", "bitmap": "bitmap0",
- "format": "qcow2", "mode": "existing",
- "sync": "incremental", "target": "d0-incr-1.qcow2" } },
- { "type": "drive-backup",
- "data": { "device": "drive1", "bitmap": "bitmap1",
- "format": "qcow2", "mode": "existing",
- "sync": "incremental", "target": "d1-incr-1.qcow2" } },
- ],
- "properties": {
- "completion-mode": "grouped"
- }
- }
- }
- ```
-
-* QMP example response, highlighting a failure for drive2:
- * Acknowledgement that the Transaction was accepted and jobs were launched:
- ```json
- { "return": {} }
- ```
-
- * Later, QEMU sends notice that the second job has errored out,
- but that the first job was also cancelled:
- ```json
- { "timestamp": { "seconds": 1447193702, "microseconds": 632377 },
- "data": { "device": "drive1", "action": "report",
- "operation": "read" },
- "event": "BLOCK_JOB_ERROR" }
- ```
-
- ```json
- { "timestamp": { "seconds": 1447193702, "microseconds": 640074 },
- "data": { "speed": 0, "offset": 0, "len": 67108864,
- "error": "Input/output error",
- "device": "drive1", "type": "backup" },
- "event": "BLOCK_JOB_COMPLETED" }
- ```
-
- ```json
- { "timestamp": { "seconds": 1447193702, "microseconds": 640163 },
- "data": { "device": "drive0", "type": "backup", "speed": 0,
- "len": 67108864, "offset": 16777216 },
- "event": "BLOCK_JOB_CANCELLED" }
- ```
-
-<!--
-The FreeBSD Documentation License
-
-Redistribution and use in source (Markdown) and 'compiled' forms (SGML, HTML,
-PDF, PostScript, RTF and so forth) with or without modification, are permitted
-provided that the following conditions are met:
-
-Redistributions of source code (Markdown) must retain the above copyright
-notice, this list of conditions and the following disclaimer of this file
-unmodified.
-
-Redistributions in compiled form (transformed to other DTDs, converted to PDF,
-PostScript, RTF and other formats) must reproduce the above copyright notice,
-this list of conditions and the following disclaimer in the documentation
and/or
-other materials provided with the distribution.
-
-THIS DOCUMENTATION IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
IS"
-AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
-IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
-DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
-FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
-DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
-SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
-CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
-OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF
-THIS DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
--->
diff --git a/docs/interop/bitmaps.rst b/docs/interop/bitmaps.rst
new file mode 100644
index 0000000..7bcfe7f
--- /dev/null
+++ b/docs/interop/bitmaps.rst
@@ -0,0 +1,555 @@
+..
+ Copyright 2015 John Snow <address@hidden> and Red Hat, Inc.
+ All rights reserved.
+
+ This file is licensed via The FreeBSD Documentation License, the full
+ text of which is included at the end of this document.
+
+====================================
+Dirty Bitmaps and Incremental Backup
+====================================
+
+- Dirty Bitmaps are objects that track which data needs to be backed up
+ for the next incremental backup.
+
+- Dirty bitmaps can be created at any time and attached to any node
+ (not just complete drives).
+
+.. contents::
+
+Dirty Bitmap Names
+------------------
+
+- A dirty bitmap's name is unique to the node, but bitmaps attached to
+ different nodes can share the same name.
+
+- Dirty bitmaps created for internal use by QEMU may be anonymous and
+ have no name, but any user-created bitmaps must have a name. There
+ can be any number of anonymous bitmaps per node.
+
+- The name of a user-created bitmap must not be empty ("").
+
+Bitmap Modes
+------------
+
+- A bitmap can be "frozen," which means that it is currently in-use by
+ a backup operation and cannot be deleted, renamed, written to, reset,
+ etc.
+
+- The normal operating mode for a bitmap is "active."
+
+Basic QMP Usage
+---------------
+
+Supported Commands
+~~~~~~~~~~~~~~~~~~
+
+- ``block-dirty-bitmap-add``
+- ``block-dirty-bitmap-remove``
+- ``block-dirty-bitmap-clear``
+
+Creation
+~~~~~~~~
+
+- To create a new bitmap, enabled, on the drive with id=drive0:
+
+.. code:: json
+
+ { "execute": "block-dirty-bitmap-add",
+ "arguments": {
+ "node": "drive0",
+ "name": "bitmap0"
+ }
+ }
+
+- This bitmap will have a default granularity that matches the cluster
+ size of its associated drive, if available, clamped to between [4KiB,
+ 64KiB]. The current default for qcow2 is 64KiB.
+
+- To create a new bitmap that tracks changes in 32KiB segments:
+
+.. code:: json
+
+ { "execute": "block-dirty-bitmap-add",
+ "arguments": {
+ "node": "drive0",
+ "name": "bitmap0",
+ "granularity": 32768
+ }
+ }
+
+Deletion
+~~~~~~~~
+
+- Bitmaps that are frozen cannot be deleted.
+
+- Deleting the bitmap does not impact any other bitmaps attached to the
+ same node, nor does it affect any backups already created from this
+ node.
+
+- Because bitmaps are only unique to the node to which they are
+ attached, you must specify the node/drive name here, too.
+
+.. code:: json
+
+ { "execute": "block-dirty-bitmap-remove",
+ "arguments": {
+ "node": "drive0",
+ "name": "bitmap0"
+ }
+ }
+
+Resetting
+~~~~~~~~~
+
+- Resetting a bitmap will clear all information it holds.
+
+- An incremental backup created from an empty bitmap will copy no data,
+ as if nothing has changed.
+
+.. code:: json
+
+ { "execute": "block-dirty-bitmap-clear",
+ "arguments": {
+ "node": "drive0",
+ "name": "bitmap0"
+ }
+ }
+
+Transactions
+------------
+
+Justification
+~~~~~~~~~~~~~
+
+Bitmaps can be safely modified when the VM is paused or halted by using
+the basic QMP commands. For instance, you might perform the following
+actions:
+
+1. Boot the VM in a paused state.
+2. Create a full drive backup of drive0.
+3. Create a new bitmap attached to drive0.
+4. Resume execution of the VM.
+5. Incremental backups are ready to be created.
+
+At this point, the bitmap and drive backup would be correctly in sync,
+and incremental backups made from this point forward would be correctly
+aligned to the full drive backup.
+
+This is not particularly useful if we decide we want to start
+incremental backups after the VM has been running for a while, for which
+we will need to perform actions such as the following:
+
+1. Boot the VM and begin execution.
+2. Using a single transaction, perform the following operations:
+
+ - Create ``bitmap0``.
+ - Create a full drive backup of ``drive0``.
+
+3. Incremental backups are now ready to be created.
+
+Supported Bitmap Transactions
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- ``block-dirty-bitmap-add``
+- ``block-dirty-bitmap-clear``
+
+The usages are identical to their respective QMP commands, but see below
+for examples.
+
+Example: New Incremental Backup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+As outlined in the justification, perhaps we want to create a new
+incremental backup chain attached to a drive.
+
+.. code:: json
+
+ { "execute": "transaction",
+ "arguments": {
+ "actions": [
+ {"type": "block-dirty-bitmap-add",
+ "data": {"node": "drive0", "name": "bitmap0"} },
+ {"type": "drive-backup",
+ "data": {"device": "drive0", "target": "/path/to/full_backup.img",
+ "sync": "full", "format": "qcow2"} }
+ ]
+ }
+ }
+
+Example: New Incremental Backup Anchor Point
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Maybe we just want to create a new full backup with an existing bitmap
+and want to reset the bitmap to track the new chain.
+
+.. code:: json
+
+ { "execute": "transaction",
+ "arguments": {
+ "actions": [
+ {"type": "block-dirty-bitmap-clear",
+ "data": {"node": "drive0", "name": "bitmap0"} },
+ {"type": "drive-backup",
+ "data": {"device": "drive0", "target":
"/path/to/new_full_backup.img",
+ "sync": "full", "format": "qcow2"} }
+ ]
+ }
+ }
+
+Incremental Backups
+-------------------
+
+The star of the show.
+
+**Nota Bene!** Only incremental backups of entire drives are supported
+for now. So despite the fact that you can attach a bitmap to any
+arbitrary node, they are only currently useful when attached to the root
+node. This is because drive-backup only supports drives/devices instead
+of arbitrary nodes.
+
+Example: First Incremental Backup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Create a full backup and sync it to the dirty bitmap, as in the
+ transactional examples above; or with the VM offline, manually create
+ a full copy and then create a new bitmap before the VM begins
+ execution.
+
+ - Let's assume the full backup is named ``full_backup.img``.
+ - Let's assume the bitmap you created is ``bitmap0`` attached to
+ ``drive0``.
+
+2. Create a destination image for the incremental backup that utilizes
+ the full backup as a backing image.
+
+ - Let's assume the new incremental image is named
+ ``incremental.0.img``.
+
+ .. code:: bash
+
+ $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
+
+3. Issue the incremental backup command:
+
+ .. code:: json
+
+ { "execute": "drive-backup",
+ "arguments": {
+ "device": "drive0",
+ "bitmap": "bitmap0",
+ "target": "incremental.0.img",
+ "format": "qcow2",
+ "sync": "incremental",
+ "mode": "existing"
+ }
+ }
+
+Example: Second Incremental Backup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+1. Create a new destination image for the incremental backup that points
+ to the previous one, e.g.: ``incremental.1.img``
+
+ .. code:: bash
+
+ $ qemu-img create -f qcow2 incremental.1.img -b incremental.0.img -F
qcow2
+
+2. Issue a new incremental backup command. The only difference here is
+ that we have changed the target image below.
+
+ .. code:: json
+
+ { "execute": "drive-backup",
+ "arguments": {
+ "device": "drive0",
+ "bitmap": "bitmap0",
+ "target": "incremental.1.img",
+ "format": "qcow2",
+ "sync": "incremental",
+ "mode": "existing"
+ }
+ }
+
+Errors
+------
+
+- In the event of an error that occurs after a backup job is
+ successfully launched, either by a direct QMP command or a QMP
+ transaction, the user will receive a ``BLOCK_JOB_COMPLETE`` event with
+ a failure message, accompanied by a ``BLOCK_JOB_ERROR`` event.
+
+- In the case of an event being cancelled, the user will receive a
+ ``BLOCK_JOB_CANCELLED`` event instead of a pair of COMPLETE and ERROR
+ events.
+
+- In either case, the incremental backup data contained within the
+ bitmap is safely rolled back, and the data within the bitmap is not
+ lost. The image file created for the failed attempt can be safely
+ deleted.
+
+- Once the underlying problem is fixed (e.g. more storage space is
+ freed up), you can simply retry the incremental backup command with
+ the same bitmap.
+
+Example
+~~~~~~~
+
+1. Create a target image:
+
+ .. code:: bash
+
+ $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
+
+2. Attempt to create an incremental backup via QMP:
+
+ .. code:: json
+
+ { "execute": "drive-backup",
+ "arguments": {
+ "device": "drive0",
+ "bitmap": "bitmap0",
+ "target": "incremental.0.img",
+ "format": "qcow2",
+ "sync": "incremental",
+ "mode": "existing"
+ }
+ }
+
+3. Receive an event notifying us of failure:
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1424709442, "microseconds": 844524 },
+ "data": { "speed": 0, "offset": 0, "len": 67108864,
+ "error": "No space left on device",
+ "device": "drive1", "type": "backup" },
+ "event": "BLOCK_JOB_COMPLETED" }
+
+4. Delete the failed incremental, and re-create the image.
+
+ .. code:: bash
+
+ $ rm incremental.0.img
+ $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2
+
+5. Retry the command after fixing the underlying problem, such as
+ freeing up space on the backup volume:
+
+ .. code:: json
+
+ { "execute": "drive-backup",
+ "arguments": {
+ "device": "drive0",
+ "bitmap": "bitmap0",
+ "target": "incremental.0.img",
+ "format": "qcow2",
+ "sync": "incremental",
+ "mode": "existing"
+ }
+ }
+
+6. Receive confirmation that the job completed successfully:
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1424709668, "microseconds": 526525 },
+ "data": { "device": "drive1", "type": "backup",
+ "speed": 0, "len": 67108864, "offset": 67108864},
+ "event": "BLOCK_JOB_COMPLETED" }
+
+Partial Transactional Failures
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Sometimes, a transaction will succeed in launching and return
+ success, but then later the backup jobs themselves may fail. It is
+ possible that a management application may have to deal with a
+ partial backup failure after a successful transaction.
+
+- If multiple backup jobs are specified in a single transaction, when
+ one of them fails, it will not interact with the other backup jobs in
+ any way.
+
+- The job(s) that succeeded will clear the dirty bitmap associated with
+ the operation, but the job(s) that failed will not. It is not "safe"
+ to delete any incremental backups that were created successfully in
+ this scenario, even though others failed.
+
+Example
+^^^^^^^
+
+- QMP example highlighting two backup jobs:
+
+ .. code:: json
+
+ { "execute": "transaction",
+ "arguments": {
+ "actions": [
+ { "type": "drive-backup",
+ "data": { "device": "drive0", "bitmap": "bitmap0",
+ "format": "qcow2", "mode": "existing",
+ "sync": "incremental", "target": "d0-incr-1.qcow2" }
},
+ { "type": "drive-backup",
+ "data": { "device": "drive1", "bitmap": "bitmap1",
+ "format": "qcow2", "mode": "existing",
+ "sync": "incremental", "target": "d1-incr-1.qcow2" }
},
+ ]
+ }
+ }
+
+- QMP example response, highlighting one success and one failure:
+
+ - Acknowledgement that the Transaction was accepted and jobs were
+ launched:
+
+ .. code:: json
+
+ { "return": {} }
+
+ - Later, QEMU sends notice that the first job was completed:
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447192343, "microseconds": 615698 },
+ "data": { "device": "drive0", "type": "backup",
+ "speed": 0, "len": 67108864, "offset": 67108864 },
+ "event": "BLOCK_JOB_COMPLETED"
+ }
+
+ - Later yet, QEMU sends notice that the second job has failed:
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447192399, "microseconds": 683015 },
+ "data": { "device": "drive1", "action": "report",
+ "operation": "read" },
+ "event": "BLOCK_JOB_ERROR" }
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447192399, "microseconds":
+ 685853 }, "data": { "speed": 0, "offset": 0, "len": 67108864,
+ "error": "Input/output error", "device": "drive1", "type":
+ "backup" }, "event": "BLOCK_JOB_COMPLETED" }
+
+- In the above example, ``d0-incr-1.qcow2`` is valid and must be kept,
+ but ``d1-incr-1.qcow2`` is invalid and should be deleted. If a VM-wide
+ incremental backup of all drives at a point-in-time is to be made,
+ new backups for both drives will need to be made, taking into account
+ that a new incremental backup for drive0 needs to be based on top of
+ ``d0-incr-1.qcow2``.
+
+Grouped Completion Mode
+~~~~~~~~~~~~~~~~~~~~~~~
+
+- While jobs launched by transactions normally complete or fail on
+ their own, it is possible to instruct them to complete or fail
+ together as a group.
+
+- QMP transactions take an optional properties structure that can
+ affect the semantics of the transaction.
+
+- The "completion-mode" transaction property can be either "individual"
+ which is the default, legacy behavior described above, or "grouped,"
+ a new behavior detailed below.
+
+- Delayed Completion: In grouped completion mode, no jobs will report
+ success until all jobs are ready to report success.
+
+- Grouped failure: If any job fails in grouped completion mode, all
+ remaining jobs will be cancelled. Any incremental backups will
+ restore their dirty bitmap objects as if no backup command was ever
+ issued.
+
+ - Regardless of if QEMU reports a particular incremental backup job
+ as CANCELLED or as an ERROR, the in-memory bitmap will be
+ restored.
+
+Example
+^^^^^^^
+
+- Here's the same example scenario from above with the new property:
+
+ .. code:: json
+
+ { "execute": "transaction",
+ "arguments": {
+ "actions": [
+ { "type": "drive-backup",
+ "data": { "device": "drive0", "bitmap": "bitmap0",
+ "format": "qcow2", "mode": "existing",
+ "sync": "incremental", "target": "d0-incr-1.qcow2" }
},
+ { "type": "drive-backup",
+ "data": { "device": "drive1", "bitmap": "bitmap1",
+ "format": "qcow2", "mode": "existing",
+ "sync": "incremental", "target": "d1-incr-1.qcow2" }
},
+ ],
+ "properties": {
+ "completion-mode": "grouped"
+ }
+ }
+ }
+
+- QMP example response, highlighting a failure for ``drive2``:
+
+ - Acknowledgement that the Transaction was accepted and jobs were
+ launched:
+
+ .. code:: json
+
+ { "return": {} }
+
+ - Later, QEMU sends notice that the second job has errored out, but
+ that the first job was also cancelled:
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447193702, "microseconds": 632377 },
+ "data": { "device": "drive1", "action": "report",
+ "operation": "read" },
+ "event": "BLOCK_JOB_ERROR" }
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447193702, "microseconds": 640074 },
+ "data": { "speed": 0, "offset": 0, "len": 67108864,
+ "error": "Input/output error",
+ "device": "drive1", "type": "backup" },
+ "event": "BLOCK_JOB_COMPLETED" }
+
+ .. code:: json
+
+ { "timestamp": { "seconds": 1447193702, "microseconds": 640163 },
+ "data": { "device": "drive0", "type": "backup", "speed": 0,
+ "len": 67108864, "offset": 16777216 },
+ "event": "BLOCK_JOB_CANCELLED" }
+
+.. raw:: html
+
+ <!--
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--
2.9.4