The following changes since commit ca4e667dbf431d4a2a5a619cde79d30dd2ac3eb2:

Merge remote-tracking branch 'remotes/kraxel/tags/usb-20170717-pull-request' into staging (2017-07-17 17:54:17 +0100)

for you to fetch changes up to 8508eee740c78d1465e25dad7c3e06137485dfbc:

live-block-ops.txt: Rename, rewrite, and improve it (2017-07-18 00:11:01 -0400)

Block patches (documentation)

Kashyap Chamarthy (2):

bitmaps.md: Convert to rST; move it into 'interop' dir

live-block-ops.txt: Rename, rewrite, and improve it

docs/devel/bitmaps.md | 505 ---------------

docs/interop/bitmaps.rst | 555 ++++++++++++++++

docs/interop/live-block-operations.rst | 1088 ++++++++++++++++++++++++++++++++

docs/live-block-ops.txt | 72 ---

4 files changed, 1643 insertions(+), 577 deletions(-)

delete mode 100644 docs/devel/bitmaps.md

create mode 100644 docs/interop/bitmaps.rst

create mode 100644 docs/interop/live-block-operations.rst

delete mode 100644 docs/live-block-ops.txt

2.9.4

From: Kashyap Chamarthy <kchamart@redhat.com>

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 <kchamart@redhat.com>

Reviewed-by: John Snow <jsnow@redhat.com>

Message-id: 20170717105205.32639-2-kchamart@redhat.com

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 XXXXXXX..XXXXXXX

--- a/docs/devel/bitmaps.md

+++ /dev/null

@@ -XXX,XX +XXX,XX @@

-<!--

-Copyright 2015 John Snow <jsnow@redhat.com> 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 XXXXXXX..XXXXXXX

--- /dev/null

+++ b/docs/interop/bitmaps.rst

@@ -XXX,XX +XXX,XX @@

+..

+ Copyright 2015 John Snow <jsnow@redhat.com> 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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+

+ 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

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+ 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.

+ -->

2.9.4

From: Kashyap Chamarthy <kchamart@redhat.com>

This patch documents (including their QMP invocations) all the four

major kinds of live block operations:

- `block-stream`

- `block-commit`

- `drive-mirror` (& `blockdev-mirror`)

- `drive-backup` (& `blockdev-backup`)

Things considered while writing this document:

- Use reStructuredText as markup language (with the goal of generating

the HTML output using the Sphinx Documentation Generator). It is

gentler on the eye, and can be trivially converted to different

formats. (Another reason: upstream QEMU is considering to switch to

Sphinx, which uses reStructuredText as its markup language.)

- Raw QMP JSON output vs. 'qmp-shell'. I debated with myself whether

to only show raw QMP JSON output (as that is the canonical

representation), or use 'qmp-shell', which takes key-value pairs. I

settled on the approach of: for the first occurrence of a command,

use raw JSON; for subsequent occurrences, use 'qmp-shell', with an

occasional exception.

- Usage of `-blockdev` command-line.

- Usage of 'node-name' vs. file path to refer to disks. While we have

`blockdev-{mirror, backup}` as 'node-name'-alternatives for

`drive-{mirror, backup}`, the `block-commit` command still operates

on file names for parameters 'base' and 'top'. So I added a caveat

at the beginning to that effect.

Refer this related thread that I started (where I learnt

`block-stream` was recently reworked to accept 'node-name' for 'top'

and 'base' parameters):

https://lists.nongnu.org/archive/html/qemu-devel/2017-05/msg06466.html

"[RFC] Making 'block-stream', and 'block-commit' accept node-name"

All commands showed in this document were tested while documenting.

Thanks: Eric Blake for the section: "A note on points-in-time vs file

names". This useful bit was originally articulated by Eric in his

KVMForum 2015 presentation, so I included that specific bit in this

document.

Signed-off-by: Kashyap Chamarthy <kchamart@redhat.com>

Reviewed-by: Eric Blake <eblake@redhat.com>

Message-id: 20170717105205.32639-3-kchamart@redhat.com

Signed-off-by: Jeff Cody <jcody@redhat.com>

---

docs/interop/live-block-operations.rst | 1088 ++++++++++++++++++++++++++++++++

docs/live-block-ops.txt | 72 ---

2 files changed, 1088 insertions(+), 72 deletions(-)

create mode 100644 docs/interop/live-block-operations.rst

delete mode 100644 docs/live-block-ops.txt

diff --git a/docs/interop/live-block-operations.rst b/docs/interop/live-block-operations.rst

new file mode 100644

index XXXXXXX..XXXXXXX

--- /dev/null

+++ b/docs/interop/live-block-operations.rst

@@ -XXX,XX +XXX,XX @@

+..

+ Copyright (C) 2017 Red Hat Inc.

+

+ This work is licensed under the terms of the GNU GPL, version 2 or

+ later. See the COPYING file in the top-level directory.

+

+============================

+Live Block Device Operations

+============================

+

+QEMU Block Layer currently (as of QEMU 2.9) supports four major kinds of

+live block device jobs -- stream, commit, mirror, and backup. These can

+be used to manipulate disk image chains to accomplish certain tasks,

+namely: live copy data from backing files into overlays; shorten long

+disk image chains by merging data from overlays into backing files; live

+synchronize data from a disk image chain (including current active disk)

+to another target image; and point-in-time (and incremental) backups of

+a block device. Below is a description of the said block (QMP)

+primitives, and some (non-exhaustive list of) examples to illustrate

+their use.

+

+.. note::

+ The file ``qapi/block-core.json`` in the QEMU source tree has the

+ canonical QEMU API (QAPI) schema documentation for the QMP

+ primitives discussed here.

+

+.. todo (kashyapc):: Remove the ".. contents::" directive when Sphinx is

+ integrated.

+

+.. contents::

+

+Disk image backing chain notation

+---------------------------------

+

+A simple disk image chain. (This can be created live using QMP

+``blockdev-snapshot-sync``, or offline via ``qemu-img``)::

+

+ (Live QEMU)

+ |

+ .

+ V

+

+ [A] <----- [B]

+

+ (backing file) (overlay)

+

+The arrow can be read as: Image [A] is the backing file of disk image

+[B]. And live QEMU is currently writing to image [B], consequently, it

+is also referred to as the "active layer".

+

+There are two kinds of terminology that are common when referring to

+files in a disk image backing chain:

+

+(1) Directional: 'base' and 'top'. Given the simple disk image chain

+ above, image [A] can be referred to as 'base', and image [B] as

+ 'top'. (This terminology can be seen in in QAPI schema file,

+ block-core.json.)

+

+(2) Relational: 'backing file' and 'overlay'. Again, taking the same

+ simple disk image chain from the above, disk image [A] is referred

+ to as the backing file, and image [B] as overlay.

+

+ Throughout this document, we will use the relational terminology.

+

+.. important::

+ The overlay files can generally be any format that supports a

+ backing file, although QCOW2 is the preferred format and the one

+ used in this document.

+

+

+Brief overview of live block QMP primitives

+-------------------------------------------

+

+The following are the four different kinds of live block operations that

+QEMU block layer supports.

+

+(1) ``block-stream``: Live copy of data from backing files into overlay

+ files.

+

+ .. note:: Once the 'stream' operation has finished, three things to

+ note:

+

+ (a) QEMU rewrites the backing chain to remove

+ reference to the now-streamed and redundant backing

+ file;

+

+ (b) the streamed file *itself* won't be removed by QEMU,

+ and must be explicitly discarded by the user;

+

+ (c) the streamed file remains valid -- i.e. further

+ overlays can be created based on it. Refer the

+ ``block-stream`` section further below for more

+ details.

+

+(2) ``block-commit``: Live merge of data from overlay files into backing

+ files (with the optional goal of removing the overlay file from the

+ chain). Since QEMU 2.0, this includes "active ``block-commit``"

+ (i.e. merge the current active layer into the base image).

+

+ .. note:: Once the 'commit' operation has finished, there are three

+ things to note here as well:

+

+ (a) QEMU rewrites the backing chain to remove reference

+ to now-redundant overlay images that have been

+ committed into a backing file;

+

+ (b) the committed file *itself* won't be removed by QEMU

+ -- it ought to be manually removed;

+