4:12 p.m.
On 06/13/2018 12:42 PM, Eric Blake wrote:
Prepare for new checkpoint and backup APIs by describing the XML
that will represent a checkpoint. This is modeled heavily after
the XML for virDomainSnapshotPtr, since both represent a point in
time of the guest. But while a snapshot exists with the intent
of rolling back to that state, a checkpoint instead makes it
possible to create an incremental backup at a later time.
Add testsuite coverage of a minimal use of the XML.
Signed-off-by: Eric Blake <eblake(a)redhat.com>
---
docs/docs.html.in | 3 +-
docs/domainstatecapture.html.in | 4 +-
docs/formatcheckpoint.html.in | 273 +++++++++++++++++++++++++++++
docs/schemas/domaincheckpoint.rng | 89 ++++++++++
libvirt.spec.in | 1 +
mingw-libvirt.spec.in | 2 +
tests/domaincheckpointxml2xmlin/empty.xml | 1 +
tests/domaincheckpointxml2xmlout/empty.xml | 10 ++
tests/virschematest.c | 2 +
9 files changed, 382 insertions(+), 3 deletions(-)
create mode 100644 docs/formatcheckpoint.html.in
create mode 100644 docs/schemas/domaincheckpoint.rng
create mode 100644 tests/domaincheckpointxml2xmlin/empty.xml
create mode 100644 tests/domaincheckpointxml2xmlout/empty.xml
diff --git a/docs/docs.html.in b/docs/docs.html.in
index 4c46b74980..11dfd27ba6 100644
--- a/docs/docs.html.in
+++ b/docs/docs.html.in
@@ -79,7 +79,8 @@
<a href="formatdomaincaps.html">domain
capabilities</a>,
<a href="formatnode.html">node devices</a>,
<a href="formatsecret.html">secrets</a>,
- <a href="formatsnapshot.html">snapshots</a></dd>
+ <a href="formatsnapshot.html">snapshots</a>,
+ <a
href="formatcheckpoint.html">checkpoints</a></dd>
<dt><a href="uri.html">URI format</a></dt>
<dd>The URI formats used for connecting to libvirt</dd>
Add a link in the format.html.in and index.html.in pages too.
diff --git a/docs/domainstatecapture.html.in
b/docs/domainstatecapture.html.in
index 00ab7e8ee1..4de93c87c8 100644
--- a/docs/domainstatecapture.html.in
+++ b/docs/domainstatecapture.html.in
@@ -154,9 +154,9 @@
time as a new backup, so that the next incremental backup can
refer to the incremental state since the checkpoint created
during the current backup. Guest state is then actually
- captured using <code>virDomainBackupBegin()</code>. <!--See
also
+ captured using <code>virDomainBackupBegin()</code>. See also
the <a href="formatcheckpoint.html">XML details</a> used
with
- this command.--></dd>
+ this command.</dd>
</dl>
<h2><a id="examples">Examples</a></h2>
diff --git a/docs/formatcheckpoint.html.in b/docs/formatcheckpoint.html.in
new file mode 100644
index 0000000000..34507a9f68
--- /dev/null
+++ b/docs/formatcheckpoint.html.in
@@ -0,0 +1,273 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE html>
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <body>
+ <h1>Checkpoint and Backup XML format</h1>
+
+ <ul id="toc"></ul>
+
+ <h2><a id="CheckpointAttributes">Checkpoint
XML</a></h2>
+
+ <p>
+ Domain disk backups, including incremental backups, are one form'
+ of <a href="domainstatecapture.html">domain
state capture</a>.
+ </p>
IMO: Strange opening line for something describing checkpoints.
As I've read further, the fact that checkpoint and backup is only
supported for qcow2 domain disks I would think needs to be up at the top
here - front an center. No sense reading any further for raw disks.
Yet another patch 2 "factor" related to choosing a backup plan. What to
do if you have raw devices and how those should be handled.
This would seem to preclude LUKS encrypted devices, true?
What about disks with various levels of backingStore logic? I can only
imagine some of the depth issues causing problems with that logic would
be applicable here too with the hierarchical approach.
+ <p>
+ Libvirt is able to facilitate incremental backups by tracking
+ disk checkpoints, or points in time against which it is easy to
s/, or/ or/
+ compute which portion of the disk has changed. Given a full
+ backup (a backup created from the creation of the disk to a
+ given point in time, coupled with the creation of a disk
s/time,/time)
+ checkpoint at that time), and an incremental backup (a backup
s/time),/time,
+ created from just the dirty portion of the disk between the
+ first checkpoint and the second backup operation), it is
+ possible to do an offline reconstruction of the state of the
+ disk at the time of the second backup, without having to copy as
s/without,/without/
+ much data as a second full backup would require. Most disk
+ checkpoints are created in concert with a backup,
s/backup,/backup/
+ via <code>virDomainBackupBegin()</code>; however,
libvirt also
+ exposes enough support to create disk checkpoints independently
+ from a backup operation,
s/operation,/operation/
+ via <code>virDomainCheckpointCreateXML()</code>.
+ </p>
NB: virDomainBackupBegin doesn't exist yet. Still a few patches away.
+ <p>
+ Attributes of libvirt checkpoints are stored as child elements of
+ the <code>domaincheckpoint</code> element. At checkpoint creation
+ time, normally only the <code>name</code>,
<code>description</code>,
+ and <code>disks</code> elements are settable; the rest of the
s/; the/. The
+ fields are ignored on creation, and will be filled in by
s/creation,/creation/
+ libvirt in for informational purposes
+ by <code>virDomainCheckpointGetXMLDesc()</code>. However, when
+ redefining a checkpoint,
+ with the <code>VIR_DOMAIN_CHECKPOINT_CREATE_REDEFINE</code> flag
+ of <code>virDomainCheckpointCreateXML()</code>, all of the XML
s/XML/XML fields/
+ described here is relevant.
s/is/are/
+ </p>
"All" of them? Even the readonly ones?
+ <p>
+ Checkpoints are maintained in a hierarchy. A domain can have a
First sentence I think should start previous paragraph...
+ current checkpoint, which is the most recent checkpoint
compared to
+ the current state of the domain (although a domain might have
+ checkpoints without a current checkpoint, if checkpoints have been
+ deleted in the meantime). Creating or reverting to a checkpoint
What is inside the parenthesis is quite confusing and perhaps "forward
thinking" considering not all checkpoint concepts are described yet.
+ sets that checkpoint as current, and the prior current
checkpoint is
+ the parent of the new checkpoint. Branches in the hierarchy can
So you can create a "current" checkpoint or revert to a checkpoint
making it current - so how then does a domain ever have checkpoints
without a current checkpoint. Is this a chicken and egg problem?
+ be formed by reverting to a checkpoint with a child, then
creating
+ another checkpoint.
Can one merge two or more checkpoints? Let's say I have A, B, C, D, and
E. I could care less about B, C, and D now and I want to merge them to
create F which is essentially all 3 sets of changes leaving the time
oriented order as A, F, E.
I still don't see how a domain doesn't have a current checkpoint even
though there are checkpoints.
+ </p>
Does the live domain maintain a pointer to the checkpoint? Or are
domaincheckpoint xml files only valid with their own context? How would
the checkpoint code know if a domain was removed? Following events?
+ <p>
+ The top-level <code>domaincheckpoint</code> element may contain
+ the following elements:
s/following/following optional/
+ </p>
> + <dl>
> + <dt><code>name</code></dt>
> + <dd>The name for this checkpoint. If the name is specified when
> + initially creating the checkpoint, then the checkpoint will have
> + that particular name. If the name is omitted when initially
> + creating the checkpoint, then libvirt will make up a name for
> + the checkpoint, based on the time when it was created.
Assuming epoch and that seems to be confirmed by the example.
+ </dd>
+ <dt><code>description</code></dt>
+ <dd>A human-readable description of the checkpoint. If the
+ description is omitted when initially creating the checkpoint,
+ then this field will be empty.
+ </dd>
+ <dt><code>disks</code></dt>
+ <dd>On input, this is an optional listing of specific
+ instructions for disk checkpoints; it is needed when making a
What does specific instructions mean in this context?
+ checkpoint on only a subset of the disks associated with a
+ domain (in particular, since qemu checkpoints require qcow2
+ disks, this element may be needed on input for excluding guest
+ disks that are not in qcow2 format); if omitted on input, then
Ah, well now you know why I added the note at the top... This is buried
inside this description.
+ all disks participate in the checkpoint. On output, this is
I have visions of sugar plum fairies and QE teams using hot (un)plug to
make life absolutely miserable in this regard.
Setting aside hot [un]plug, this makes it's possible to define a subset
of domain qcow2 disks to participate in the checkpoint/backup, fair
statement? If not provided, then all qcow2 disks participate.
+ fully populated to show the state of each disk in the
+ checkpoint. This element has a list of <code>disk</code>
+ sub-elements, describing anywhere from one to all of the disks
s/the/the qcow2 formatted/
+ associated with the domain.
+ <dl>
+ <dt><code>disk</code></dt>
+ <dd>This sub-element describes the checkpoint properties of
+ a specific disk. The attribute <code>name</code> is
+ mandatory, and must match either the <code><target
+ dev='name'/></code> or an unambiguous
<code><source
+ file='name'/></code> of one of
+ the <a href="formatdomain.html#elementsDisks">disk
+ devices</a> specified for the domain at the time of the
I honestly think you should just pick one the target dev and be done,
but I assume there's a reason for both which I don't understand yet.
+ checkpoint. The attribute
<code>checkpoint</code> is
+ optional on input; possible values are <code>no</code>
+ when the disk does not participate in this checkpoint;
+ or <code>bitmap</code> if the disk will track all changes
+ since the creation of this checkpoint via a bitmap, in
+ which case another attribute <code>bitmap</code> will be
+ the name of the tracking bitmap (defaulting to the
+ checkpoint name).
So now I'm confused again. Initially it seemed as though the <disk>
sub-elements would be the only ones participating, but now it feels like
it's possible to pick and choose to what level something participates.
If nothing is provided, can someone change the 'checkpoint' attribute to
'no' (assuming the default is 'bitmap')? This is all rather mind
boggling - why can stuff never be simple /-|
+ </dd>
+ </dl>
+ </dd>
+ <dt><code>creationTime</code></dt>
+ <dd>The time this checkpoint was created. The time is specified
+ in seconds since the Epoch, UTC (i.e. Unix time). Readonly.
+ </dd>
+ <dt><code>parent</code></dt>
+ <dd>The parent of this checkpoint. If present, this element
+ contains exactly one child element, name. This specifies the
+ name of the parent checkpoint of this one, and is used to
+ represent trees of checkpoints. Readonly.
+ </dd>
+ <dt><code>domain</code></dt>
+ <dd>The inactive <a href="formatdomain.html">domain
+ configuration</a> at the time the checkpoint was created.
+ Readonly.
The whole initial inactive/config XML is loaded here? Or just certain
fields. The example XML output has just a UUID, but the data here has a
lot more and the RNG shows everything.
Did I read something wrong earlier regarding saving domain state? I
though the checkpoint/backup code was purely for the domain disks that
are of type qcow2. I can see saving the UUID since that cannot change
(unlike the name)... But why does the entire "original" config need to
be added here?
> + </dd>
> + </dl>
> +
> + <h2><a id="BackupAttributes">Backup
XML</a></h2>
> +
> + <p>
> + Creating a backup, whether full or incremental, is done
> + via <code>virDomainBackupBegin()</code>, which takes an XML
> + description of the actions to perform. There are two general
> + modes for backups: a push mode (where the hypervisor writes out
> + the data to the destination file, which may be local or remote),
> + and a pull mode (where the hypervisor creates an NBD server that
> + a third-party client can then read as needed, and which requires
> + the use of temporary storage, typically local, until the backup
> + is complete).
+ </p>
I think the modes should be described in own bullets rather than part of
a long-ish sentence using parentheses to help define what is meant.
Perhaps even more verbiage regarding general usage expectations of each
model.
+ <p>
+ The instructions for beginning a backup job are provided as
+ attributes and elements of the
+ top-level <code>domainbackup</code> element. This element
+ includes an optional attribute <code>mode</code> which can be
+ either "push" or "pull" (default push). Where elements are
s/Where/Although ???
+ optional on creation,
<code>virDomainBackupGetXMLDesc()</code>
+ can be used to see the actual values selected (for example,
+ learning which port the NBD server is using in the pull model,
s/model,/model/
> + or what file names libvirt generated when none were supplied).
> + The following child elements are supported:
+ </p>
> + <dl>
Since all elements are optional, probably don't have to note it again
for each description...
+ <dt><code>incremental</code></dt>
+ <dd>Optional. If this element is present, it must name an
+ existing checkpoint of the domain, which will be used to make
s/domain,/domain/
+ this backup an incremental one (in the push model, only
+ changes since the checkpoint are written to the destination;
+ in the pull model, the NBD server uses the
+ NBD_OPT_SET_META_CONTEXT extension to advertise to the client
+ which portions of the export contain changes since the
+ checkpoint). If omitted, a full backup is performed.
The wording in the parentheses doesn't make complete sense yet.
Perhaps it's better to have each as a bullet describing the action of
the element for the backup "mode" value.
+ </dd>
+ <dt><code>server</code></dt>
+ <dd>Present only for a pull mode backup. Contains the same
+ attributes as the <code>protocol</code> element of a disk
+ attached via NBD in the domain (such as transport, socket,
+ name, port, or tls), necessary to set up an NBD server that
+ exposes the content of each disk at the time the backup
contents ?
+ started.
+ </dd>
This hunk above uses <tab>'s not spaces (syntax-check)
+ <dt><code>disks</code></dt>
+ <dd>This is an optional listing of instructions for disks
+ participating in the backup (if omitted, all disks
+ participate, and libvirt attempts to generate filenames by
+ appending the current timestamp as a suffix). When provided on
+ input, disks omitted from the list do not participate in the
+ backup. On output, the list is present but contains only the
+ disks participating in the backup job. This element has a
+ list of <code>disk</code> sub-elements, describing anywhere
+ from one to all of the disks associated with the domain.
again, qcow2 formatted disks, right? Is that true for both mode's of
backup?
+ <dl>
+ <dt><code>disk</code></dt>
+ <dd>This sub-element describes the checkpoint properties of
+ a specific disk. The attribute <code>name</code> is
+ mandatory, and must match either the <code><target
+ dev='name'/></code> or an unambiguous
<code><source
+ file='name'/></code> of one of
+ the <a href="formatdomain.html#elementsDisks">disk
+ devices</a> specified for the domain at the time of the
+ checkpoint. The optional attribute <code>type</code> can
+ be <code>file</code>, <code>block</code>,
+ or <code>networks</code>, similar to a disk declaration
network
+ for a domain, controls what additional sub-elements are
s/,/ and/
+ needed to describe the destination (such
+ as <code>protocol</code> for a network destination). In
+ push mode backups, the primary subelement
sub-element
+ is <code>target</code>; in pull mode, the
primary sublement
sub-element
+ is <code>scratch</code>; but either way,
+ the primary sub-element describes the file name to be used
+ during the backup operation, similar to
+ the <code>source</code> sub-element of a domain disk. An
+ optional sublement <code>driver</code> can also be used to
sub-element
+ specify a destination format different from qcow2.
+ </dd>
+ </dl>
+ </dd>
+ </dl>
Well, suffice to say, I'm lost. I guess I at least am getting an idea
why no consensus has been reached yet.
> +
> + <h2><a id="example">Examples</a></h2>
> +
> + <p>Using this XML to create a checkpoint of just vda on a qemu
> + domain with two disks and a prior checkpoint:</p>
> + <pre>
> +<domaincheckpoint>
> + <description>Completion of updates after OS
install</description>
> + <disks>
> + <disk name='vda' checkpoint='bitmap'/>
> + <disk name='vdb' checkpoint='no'/>
> + </disks>
> +</domaincheckpoint></pre>
> +
> + <p>will result in XML similar to this from
> + <code>virDomainCheckpointGetXMLDesc()</code>:</p>
> + <pre>
> +<domaincheckpoint>
> + <name>1525889631</name>
> + <description>Completion of updates after OS
install</description>
> + <creationTime>1525889631</creationTime>
> + <parent>
> + <name>1525111885</name>
> + </parent>
> + <disks>
> + <disk name='vda' checkpoint='bitmap'
bitmap='1525889631'/>
> + <disk name='vdb' checkpoint='no'/>
> + </disks>
> + <domain>
> + <name>fedora</name>
> + <uuid>93a5c045-6457-2c09-e56c-927cdf34e178</uuid>
> + <memory>1048576</memory>
> + ...
> + <devices>
> + <disk type='file' device='disk'>
> + <driver name='qemu' type='qcow2'/>
> + <source file='/path/to/file1'/>
> + <target dev='vda' bus='virtio'/>
> + </disk>
> + <disk type='file' device='disk'
snapshot='external'>
> + <driver name='qemu' type='raw'/>
> + <source file='/path/to/file2'/>
> + <target dev='vdb' bus='virtio'/>
> + </disk>
> + ...
> + </devices>
> + </domain>
> +</domaincheckpoint></pre>
> +
> + <p>With that checkpoint created, the qcow2 image is now tracking
> + all changes that occur in the image since the checkpoint via
> + the persistent bitmap named <code>1525889631</code>. Now, we
> + can make a subsequent call
> + to <code>virDomainBackupBegin()</code> to perform an incremental
> + backup of just this data, using the following XML to start a
> + pull model NBD export of the vda disk:
+ </p>
> + <pre>
> +<domainbackup mode="pull">
> + <incremental>1525889631</incremental>
> + <server transport="unix"
socket="/path/to/server"/>
> + <disks/>
> + <disk name='vda' type='file'/>
> + <scratch file=/path/to/file1.scratch'/>
> + </disk>
> + </disks/>
> +</domainbackup>
> + </pre>
> + </body>
> +</html>
> diff --git a/docs/schemas/domaincheckpoint.rng b/docs/schemas/domaincheckpoint.rng
> new file mode 100644
> index 0000000000..1e2c16e035
> --- /dev/null
> +++ b/docs/schemas/domaincheckpoint.rng
> @@ -0,0 +1,89 @@
> +<?xml version="1.0"?>
> +<!-- A Relax NG schema for the libvirt domain checkpoint properties XML format
-->
> +<grammar xmlns="http://relaxng.org/ns/structure/1.0">
> + <start>
> + <ref name='domaincheckpoint'/>
> + </start>
> +
> + <include href='domaincommon.rng'/>
> +
> + <define name='domaincheckpoint'>
> + <element name='domaincheckpoint'>
> + <interleave>
> + <optional>
> + <element name='name'>
> + <text/>
> + </element>
> + </optional>
> + <optional>
> + <element name='description'>
> + <text/>
> + </element>
> + </optional>
> + <optional>
> + <element name='creationTime'>
> + <text/>
> + </element>
> + </optional>
> + <optional>
> + <element name='disks'>
> + <zeroOrMore>
> + <ref name='diskcheckpoint'/>
> + </zeroOrMore>
> + </element>
> + </optional>
> + <optional>
> + <choice>
> + <element name='domain'>
> + <element name='uuid'>
> + <ref name="UUID"/>
> + </element>
> + </element>
> + <!-- Nested grammar ensures that any of our overrides of
> + storagecommon/domaincommon defines do not conflict
> + with any domain.rng overrides. -->
> + <grammar>
> + <include href='domain.rng'/>
> + </grammar>
> + </choice>
> + </optional>
> + <optional>
> + <element name='parent'>
> + <element name='name'>
> + <text/>
> + </element>
> + </element>
> + </optional>
> + </interleave>
> + </element>
> + </define>
Since everything is optional, does <optional> have be supplied for each
element or can there be one <optional> before the <interleave>?
I see no <domainbackup> definition yet either - I assume it's coming.
John
+
+ <define name='diskcheckpoint'>
+ <element name='disk'>
+ <attribute name='name'>
+ <choice>
+ <ref name='diskTarget'/>
+ <ref name='absFilePath'/>
+ </choice>
+ </attribute>
+ <choice>
+ <attribute name='checkpoint'>
+ <value>no</value>
+ </attribute>
+ <group>
+ <optional>
+ <attribute name='checkpoint'>
+ <value>bitmap</value>
+ </attribute>
+ </optional>
+ <optional>
+ <attribute name='bitmap'>
+ <text/>
+ </attribute>
+ </optional>
+ </group>
+ </choice>
+ </element>
+ </define>
+
+</grammar>
diff --git a/libvirt.spec.in b/libvirt.spec.in
index ace05820aa..50bd79a7d7 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -2044,6 +2044,7 @@ exit 0
%{_datadir}/libvirt/schemas/cputypes.rng
%{_datadir}/libvirt/schemas/domain.rng
%{_datadir}/libvirt/schemas/domaincaps.rng
+%{_datadir}/libvirt/schemas/domaincheckpoint.rng
%{_datadir}/libvirt/schemas/domaincommon.rng
%{_datadir}/libvirt/schemas/domainsnapshot.rng
%{_datadir}/libvirt/schemas/interface.rng
diff --git a/mingw-libvirt.spec.in b/mingw-libvirt.spec.in
index 917d2143d8..6912527cf7 100644
--- a/mingw-libvirt.spec.in
+++ b/mingw-libvirt.spec.in
@@ -241,6 +241,7 @@ rm -rf $RPM_BUILD_ROOT%{mingw64_libexecdir}/libvirt-guests.sh
%{mingw32_datadir}/libvirt/schemas/cputypes.rng
%{mingw32_datadir}/libvirt/schemas/domain.rng
%{mingw32_datadir}/libvirt/schemas/domaincaps.rng
+%{mingw32_datadir}/libvirt/schemas/domaincheckpoint.rng
%{mingw32_datadir}/libvirt/schemas/domaincommon.rng
%{mingw32_datadir}/libvirt/schemas/domainsnapshot.rng
%{mingw32_datadir}/libvirt/schemas/interface.rng
@@ -326,6 +327,7 @@ rm -rf $RPM_BUILD_ROOT%{mingw64_libexecdir}/libvirt-guests.sh
%{mingw64_datadir}/libvirt/schemas/cputypes.rng
%{mingw64_datadir}/libvirt/schemas/domain.rng
%{mingw64_datadir}/libvirt/schemas/domaincaps.rng
+%{mingw32_datadir}/libvirt/schemas/domaincheckpoint.rng
%{mingw64_datadir}/libvirt/schemas/domaincommon.rng
%{mingw64_datadir}/libvirt/schemas/domainsnapshot.rng
%{mingw64_datadir}/libvirt/schemas/interface.rng
diff --git a/tests/domaincheckpointxml2xmlin/empty.xml
b/tests/domaincheckpointxml2xmlin/empty.xml
new file mode 100644
index 0000000000..dc36449142
--- /dev/null
+++ b/tests/domaincheckpointxml2xmlin/empty.xml
@@ -0,0 +1 @@
+<domaincheckpoint/>
diff --git a/tests/domaincheckpointxml2xmlout/empty.xml
b/tests/domaincheckpointxml2xmlout/empty.xml
new file mode 100644
index 0000000000..a26c7caab0
--- /dev/null
+++ b/tests/domaincheckpointxml2xmlout/empty.xml
@@ -0,0 +1,10 @@
+<domaincheckpoint>
+ <name>1525889631</name>
+ <creationTime>1525889631</creationTime>
+ <disks>
+ <disk name='vda' checkpoint='bitmap'
bitmap='1525889631'/>
+ </disks>
+ <domain>
+ <uuid>9d37b878-a7cc-9f9a-b78f-49b3abad25a8</uuid>
+ </domain>
+</domaincheckpoint>
diff --git a/tests/virschematest.c b/tests/virschematest.c
index 2d35833919..b866db4326 100644
--- a/tests/virschematest.c
+++ b/tests/virschematest.c
@@ -223,6 +223,8 @@ mymain(void)
"genericxml2xmloutdata", "xlconfigdata",
"libxlxml2domconfigdata",
"qemuhotplugtestdomains");
DO_TEST_DIR("domaincaps.rng", "domaincapsschemadata");
+ DO_TEST_DIR("domaincheckpoint.rng",
"domaincheckpointxml2xmlin",
+ "domaincheckpointxml2xmlout");
DO_TEST_DIR("domainsnapshot.rng", "domainsnapshotxml2xmlin",
"domainsnapshotxml2xmlout");
DO_TEST_DIR("interface.rng", "interfaceschemadata");