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libvirt/docs/formatsnapshot.html.in
Eric Blake f609cb85ca snapshot: allow full domain xml in snapshot
Just like VM saved state images (virsh save), snapshots MUST
track the inactive domain xml to detect any ABI incompatibilities.

The indentation is not perfect, but functionality comes before form.

Later patches will actually supply a full domain; for now, this
wires up the storage to support one, but doesn't ever generate one
in dumpxml output.

Happily, libvirt.c was already rejecting use of VIR_DOMAIN_XML_SECURE
from read-only connections, even though before this patch, there was
no information to be secured by the use of that flag.

And while we're at it, mark the libvirt snapshot metadata files
as internal-use only.

* src/libvirt.c (virDomainSnapshotGetXMLDesc): Document flag.
* src/conf/domain_conf.h (_virDomainSnapshotDef): Add member.
(virDomainSnapshotDefParseString, virDomainSnapshotDefFormat):
Update signature.
* src/conf/domain_conf.c (virDomainSnapshotDefFree): Clean up.
(virDomainSnapshotDefParseString): Optionally parse domain.
(virDomainSnapshotDefFormat): Output full domain.
* src/esx/esx_driver.c (esxDomainSnapshotCreateXML)
(esxDomainSnapshotGetXMLDesc): Update callers.
* src/vbox/vbox_tmpl.c (vboxDomainSnapshotCreateXML)
(vboxDomainSnapshotGetXMLDesc): Likewise.
* src/qemu/qemu_driver.c (qemuDomainSnapshotCreateXML)
(qemuDomainSnapshotLoad, qemuDomainSnapshotGetXMLDesc)
(qemuDomainSnapshotWriteMetadata): Likewise.
* docs/formatsnapshot.html.in: Rework doc example.
Based on a patch by Philipp Hahn.
2011-09-03 08:09:35 -06:00

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<html>
<body>
<h1>Snapshot XML format</h1>
<ul id="toc"></ul>
<h2><a name="SnapshotAttributes">Snapshot XML</a></h2>
<p>
Attributes of libvirt snapshots are stored as child elements of
the <code>domainsnapshot</code> element. At snapshot creation
time, normally only the <code>name</code>
and <code>description</code> elements are settable; the rest of
the fields are ignored on creation, and will be filled in by
libvirt in for informational purposes
by <code>virDomainSnapshotGetXMLDesc()</code>. However, when
redefining a snapshot (<span class="since">since 0.9.5</span>),
with the <code>VIR_DOMAIN_SNAPSHOT_CREATE_REDEFINE</code> flag
of <code>virDomainSnapshotCreateXML()</code>, all of the XML
described here is relevant.
</p>
<p>
Snapshots are maintained in a hierarchy. A domain can have a
current snapshot, which is the most recent snapshot compared to
the current state of the domain (although a domain might have
snapshots without a current snapshot, if snapshots have been
deleted in the meantime). Creating or reverting to a snapshot
sets that snapshot as current, and the prior current snapshot is
the parent of the new snapshot. Branches in the hierarchy can
be formed by reverting to a snapshot with a child, then creating
another snapshot.
</p>
<p>
The top-level <code>domainsnapshot</code> element may contain
the following elements:
</p>
<dl>
<dt><code>name</code></dt>
<dd>The name for this snapshot. If the name is specified when
initially creating the snapshot, then the snapshot will have
that particular name. If the name is omitted when initially
creating the snapshot, then libvirt will make up a name for
the snapshot, based on the time when it was created.
</dd>
<dt><code>description</code></dt>
<dd>A human-readable description of the snapshot. If the
description is omitted when initially creating the snapshot,
then this field will be empty.
</dd>
<dt><code>creationTime</code></dt>
<dd>The time this snapshot was created. The time is specified
in seconds since the Epoch, UTC (i.e. Unix time). Readonly.
</dd>
<dt><code>state</code></dt>
<dd>The state of the domain at the time this snapshot was taken.
When the domain is reverted to this snapshot, the domain's
state will default to whatever is in this field. Readonly.
</dd>
<dt><code>parent</code></dt>
<dd>The parent of this snapshot. This element contains exactly
one child element, name. This specifies the name of the parent
snapshot of this snapshot, and is used to represent trees of
snapshots, as described above. Readonly.
</dd>
<dt><code>domain</code></dt>
<dd>The domain that this snapshot was taken against. Older
versions of libvirt stored only a single child element, uuid;
reverting to a snapshot like this is risky if the current
state of the domain differs from the state that the domain was
created in, and requires the use of the
<code>VIR_DOMAIN_SNAPSHOT_REVERT_FORCE</code> flag
in <code>virDomainRevertToSnapshot()</code>. Newer versions
of libvirt store the entire
inactive <a href="formatdomain.html">domain configuration</a>
at the time of the snapshot (<span class="since">since
0.9.5</span>). Readonly.
</dd>
</dl>
<h2><a name="example">Examples</a></h2>
<p>Using this XML on creation:</p>
<pre>
&lt;domainsnapshot&gt;
&lt;description&gt;Snapshot of OS install and updates&lt;/description&gt;
&lt;/domainsnapshot&gt;</pre>
<p>will result in XML similar to this from
virDomainSnapshotGetXMLDesc:</p>
<pre>
&lt;domainsnapshot&gt;
&lt;name&gt;1270477159&lt;/name&gt;
&lt;description&gt;Snapshot of OS install and updates&lt;/description&gt;
&lt;state&gt;running&lt;/state&gt;
&lt;creationTime&gt;1270477159&lt;/creationTime&gt;
&lt;parent&gt;
&lt;name&gt;bare-os-install&lt;/name&gt;
&lt;/parent&gt;
&lt;domain&gt;
&lt;name&gt;fedora&lt;/name&gt;
&lt;uuid&gt;93a5c045-6457-2c09-e56c-927cdf34e178&lt;/uuid&gt;
&lt;memory&gt;1048576&lt;/memory&gt;
...
&lt;/devices&gt;
&lt;/domain&gt;
&lt;/domainsnapshot&gt;</pre>
</body>
</html>