Re: [PATCH 06/10] conf: Add VM Generation ID parse/format support

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On Wed, Apr 11, 2018 at 10:10 PM +0200, John Ferlan <jferlan@xxxxxxxxxx> wrote:
> The VM Generation ID is a mechanism to provide a unique 128-bit,
> cryptographically random, and integer value identifier known as
> the GUID (Globally Unique Identifier) to the guest OS. The value
> is used to help notify the guest operating system when the virtual
> machine is executed with a different configuration.
>
> This patch adds support for a new "genid" XML element similar to
> the "uuid" element. The "genid" element can have two forms "<genid/>"
> or "<genid>$GUID</genid>". If the $GUID is not provided, libvirt
> will generate one.
>
> For the ABI checks add avoidance for the genid comparison if the
> appropriate flag is set.
>
> Since adding support for a generated GUID (or UUID like) value to
> be displayed only for an active guest, modifying the xml2xml test
> to include virrandommock.so is necessary since it will generate a
> "known" UUID value that can be compared against for the active test.
>
> Signed-off-by: John Ferlan <jferlan@xxxxxxxxxx>
> ---
>  docs/formatdomain.html.in                        | 29 ++++++++++++
>  docs/schemas/domaincommon.rng                    |  8 ++++
>  src/conf/domain_conf.c                           | 59 ++++++++++++++++++++++++
>  src/conf/domain_conf.h                           |  3 ++
>  tests/qemuxml2argvdata/genid-auto.xml            | 32 +++++++++++++
>  tests/qemuxml2argvdata/genid.xml                 | 32 +++++++++++++
>  tests/qemuxml2xmloutdata/genid-active.xml        | 32 +++++++++++++
>  tests/qemuxml2xmloutdata/genid-auto-active.xml   | 32 +++++++++++++
>  tests/qemuxml2xmloutdata/genid-auto-inactive.xml | 32 +++++++++++++
>  tests/qemuxml2xmloutdata/genid-inactive.xml      | 32 +++++++++++++
>  tests/qemuxml2xmltest.c                          |  5 +-
>  11 files changed, 295 insertions(+), 1 deletion(-)
>  create mode 100644 tests/qemuxml2argvdata/genid-auto.xml
>  create mode 100644 tests/qemuxml2argvdata/genid.xml
>  create mode 100644 tests/qemuxml2xmloutdata/genid-active.xml
>  create mode 100644 tests/qemuxml2xmloutdata/genid-auto-active.xml
>  create mode 100644 tests/qemuxml2xmloutdata/genid-auto-inactive.xml
>  create mode 100644 tests/qemuxml2xmloutdata/genid-inactive.xml
>
> diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> index 5e99884dc5..fe9c3b19f0 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -34,6 +34,7 @@
>  &lt;domain type='kvm' id='1'&gt;
>    &lt;name&gt;MyGuest&lt;/name&gt;
>    &lt;uuid&gt;4dea22b3-1d52-d8f3-2516-782e98ab3fa0&lt;/uuid&gt;
> +  &lt;genid&gt;43dc0cf8-809b-4adb-9bea-a9abb5f3d90e&lt;/genid&gt;
>    &lt;title&gt;A short description - title - of the domain&lt;/title&gt;
>    &lt;description&gt;Some human readable description&lt;/description&gt;
>    &lt;metadata&gt;
> @@ -61,6 +62,34 @@
>          specification. <span class="since">Since 0.0.1, sysinfo
>          since 0.8.7</span></dd>
>
> +      <dt><code>genid</code></dt>
> +      <dd><span class="since">Since 4.3.0</span>, the <code>genid</code>
> +        element can be used to add a Virtual Machine Generation ID which
> +        exposes a 128-bit, cryptographically random, integer value identifier,
> +        referred to as a Globally Unique Identifier (GUID) using the same
> +        format as the <code>uuid</code>. The value is used to help notify
> +        the guest operating system when the virtual machine is executed
> +        with a different configuration, such as:
> +
> +        <ul>
> +          <li>snapshot execution</li>
> +          <li>backup recovery</li>
> +          <li>failover in a disaster recovery environment</li>
> +          <li>creation from template (import, copy, clone)</li>
> +        </ul>
> +
> +        The guest operating system notices the change and is then able to
> +        react as appropriate by marking its copies of distributed databases
> +        as dirty, re-initializing its random number generator, etc.
> +
> +        <p>
> +        When a GUID value is not provided, e.g. using the XML syntax
> +        &lt;genid/&gt;, then libvirt will automatically generate a GUID.
> +        This is the recommended configuration since the hypervisor then
> +        can handle changing the GUID value for specific state transitions.
> +        Using a static GUID value may result in failures for starting from
> +        snapshot, restoring from backup, starting a cloned domain, etc.</p></dd>
> +
>        <dt><code>title</code></dt>
>        <dd>The optional element <code>title</code> provides space for a
>          short description of the domain. The title should not contain
> diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
> index 4cab55f05d..1892a7c63c 100644
> --- a/docs/schemas/domaincommon.rng
> +++ b/docs/schemas/domaincommon.rng
> @@ -502,6 +502,14 @@
>            <ref name="UUID"/>
>          </element>
>        </optional>
> +      <optional>
> +        <element name="genid">
> +          <choice>
> +            <ref name="UUID"/>
> +            <empty/>
> +          </choice>
> +        </element>
> +      </optional>
>      </interleave>
>    </define>
>    <define name="idmap">
> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 385ba4ce8c..0fa9386270 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -18791,6 +18791,34 @@ virDomainDefParseXML(xmlDocPtr xml,
>          VIR_FREE(tmp);
>      }
>
> +    /* Extract domain genid - a genid can either be provided or generated */
> +    if ((n = virXPathNodeSet("./genid", ctxt, &nodes)) < 0)
> +        goto error;
> +
> +    if (n > 0) {
> +        if (n != 1) {
> +            virReportError(VIR_ERR_XML_ERROR, "%s",
> +                          _("element 'genid' can only appear once"));
> +            goto error;
> +        }
> +        def->genidRequested = true;
> +        if (!(tmp = virXPathString("string(./genid[1])", ctxt))) {
> +            if (virUUIDGenerate(def->genid) < 0) {
> +                virReportError(VIR_ERR_INTERNAL_ERROR,
> +                               "%s", _("Failed to generate genid"));
> +                goto error;
> +            }
> +            def->genidGenerated = true;
> +        } else {
> +            if (virUUIDParse(tmp, def->genid) < 0) {

You haven’t added these struct members to _virDomainDef (genid and
genidRequested) anywhere.

> +                virReportError(VIR_ERR_INTERNAL_ERROR,
> +                               "%s", _("malformed genid element"));
> +                goto error;
> +            }
> +        }
> +    }

[…snip]

--
Beste Grüße / Kind regards
   Marc Hartmayer

IBM Deutschland Research & Development GmbH
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Geschäftsführung: Dirk Wittkopp
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