[libvirt] [PATCH v2 06/11] conf: Add VM Generation ID parse/format support
Peter Krempa
pkrempa at redhat.com
Tue Apr 24 07:21:59 UTC 2018
On Mon, Apr 23, 2018 at 20:00:00 -0400, John Ferlan 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 at redhat.com>
> ---
> 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 ada0df227f..6a140f3e40 100644
> --- a/docs/formatdomain.html.in
> +++ b/docs/formatdomain.html.in
> @@ -34,6 +34,7 @@
> <domain type='kvm' id='1'>
> <name>MyGuest</name>
> <uuid>4dea22b3-1d52-d8f3-2516-782e98ab3fa0</uuid>
> + <genid>43dc0cf8-809b-4adb-9bea-a9abb5f3d90e</genid>
Since we encourage to use the variant with this being empty I'd show
that here.
> <title>A short description - title - of the domain</title>
> <description>Some human readable description</description>
> <metadata>
> @@ -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
> + <genid/>, 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/src/conf/domain_conf.c b/src/conf/domain_conf.c
> index 6d4db50998..8c30adf850 100644
> --- a/src/conf/domain_conf.c
> +++ b/src/conf/domain_conf.c
> @@ -18793,6 +18793,34 @@ 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"));
Generating this here is pointless, the code using it throws this away
and generates a new one. While we don't show this value to the user and
thus don't create any false impressions I think that the logic should be
shuffled around so that it's generated only when it's required.
> + }
> + def->genidGenerated = true;
> + } else {
> + if (virUUIDParse(tmp, def->genid) < 0) {
> + virReportError(VIR_ERR_INTERNAL_ERROR,
> + "%s", _("malformed genid element"));
> + goto error;
> + }
> + }
> + }
> + VIR_FREE(nodes);
> +
> /* Extract short description of domain (title) */
> def->title = virXPathString("string(./title[1])", ctxt);
> if (def->title && strchr(def->title, '\n')) {
> @@ -21904,6 +21932,26 @@ virDomainDefCheckABIStabilityFlags(virDomainDefPtr src,
> goto error;
> }
>
> + if (src->genidRequested != dst->genidRequested) {
> + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
> + _("Target domain requested genid does not match source"));
> + goto error;
> + }
> +
> + if (src->genidRequested &&
> + !(flags & VIR_DOMAIN_DEF_ABI_CHECK_SKIP_GENID) &&
The above change will also possibly remove the need for this flag. In
cases when it needs to change (snapshots) the code is skipping the check
anyways. In cases when it needs to stay the same we will know that since
it will be filled in.
> + memcmp(src->genid, dst->genid, VIR_UUID_BUFLEN) != 0) {
> + char guidsrc[VIR_UUID_STRING_BUFLEN];
> + char guiddst[VIR_UUID_STRING_BUFLEN];
> +
> + virUUIDFormat(src->genid, guidsrc);
> + virUUIDFormat(dst->genid, guiddst);
> + virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
> + _("Target domain genid %s does not match source %s"),
> + guiddst, guidsrc);
> + goto error;
> + }
> +
> /* Not strictly ABI related, but we want to make sure domains
> * don't get silently re-named through the backdoor when passing
> * custom XML into various APIs, since this would create havoc
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