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Re: [libvirt] [PATCH v2] snapshot: Store both config and live XML in the snapshot domain



On Tue, Jul 23, 2019 at 16:47:05 -0300, Maxiwell S. Garcia wrote:
> The snapshot-create operation of running guests saves the live
> XML and uses it to replace the active and inactive domain in
> case of revert. So, the config XML is ignored by the snapshot
> process. This commit changes it and adds the config XML in the
> snapshot XML as the <inactiveDomain> entry.
> 
> In case of offline guest, the behavior remains the same and the
> config XML is saved in the snapshot XML as <domain> entry. The
> behavior of older snapshots of running guests, that don't have
> the new <inactiveDomain>, remains the same too. The revert, in
> this case, overrides both active and inactive domain with the
> <domain> entry. So, the <inactiveDomain> in the snapshot XML is
> not required to snapshot work, but it's useful to preserve the
> config XML of running guests.
> 
> Signed-off-by: Maxiwell S. Garcia <maxiwell linux ibm com>
> ---
>  src/conf/moment_conf.c   |  1 +
>  src/conf/moment_conf.h   | 11 +++++++++
>  src/conf/snapshot_conf.c | 48 +++++++++++++++++++++++++++++++++++-----
>  src/qemu/qemu_driver.c   | 27 +++++++++++++++++-----
>  src/util/virxml.c        | 45 +++++++++++++++++++++++++++++++++++++
>  src/util/virxml.h        |  8 +++++++
>  6 files changed, 130 insertions(+), 10 deletions(-)
> 
> diff --git a/src/conf/moment_conf.c b/src/conf/moment_conf.c
> index fea13f0f97..f54a44b33e 100644
> --- a/src/conf/moment_conf.c
> +++ b/src/conf/moment_conf.c
> @@ -66,6 +66,7 @@ virDomainMomentDefDispose(void *obj)
>      VIR_FREE(def->description);
>      VIR_FREE(def->parent_name);
>      virDomainDefFree(def->dom);
> +    virDomainDefFree(def->inactiveDom);
>  }
>  
>  /* Provide defaults for creation time and moment name after parsing XML */
> diff --git a/src/conf/moment_conf.h b/src/conf/moment_conf.h
> index 9fdbef2172..70cc47bd70 100644
> --- a/src/conf/moment_conf.h
> +++ b/src/conf/moment_conf.h
> @@ -36,7 +36,18 @@ struct _virDomainMomentDef {
>      char *parent_name;
>      long long creationTime; /* in seconds */
>  
> +    /*
> +     * Store the active domain definition in case of online
> +     * guest and the inactive domain definition in case of
> +     * offline guest
> +     */
>      virDomainDefPtr dom;
> +
> +    /*
> +     * Store the inactive domain definition in case of online
> +     * guest and leave NULL in case of offline guest
> +     */
> +    virDomainDefPtr inactiveDom;
>  };
>  
>  virClassPtr virClassForDomainMomentDef(void);
> diff --git a/src/conf/snapshot_conf.c b/src/conf/snapshot_conf.c
> index 324901a560..8aeac9ab20 100644
> --- a/src/conf/snapshot_conf.c
> +++ b/src/conf/snapshot_conf.c
> @@ -243,6 +243,8 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
>      char *memoryFile = NULL;
>      bool offline = !!(flags & VIR_DOMAIN_SNAPSHOT_PARSE_OFFLINE);
>      virSaveCookieCallbacksPtr saveCookie = virDomainXMLOptionGetSaveCookie(xmlopt);
> +    int domainflags = VIR_DOMAIN_DEF_PARSE_INACTIVE |
> +                      VIR_DOMAIN_DEF_PARSE_SKIP_VALIDATE;
>  
>      if (!(def = virDomainSnapshotDefNew()))
>          return NULL;
> @@ -292,8 +294,6 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
>           * clients will have to decide between best effort
>           * initialization or outright failure.  */
>          if ((tmp = virXPathString("string(./domain/@type)", ctxt))) {
> -            int domainflags = VIR_DOMAIN_DEF_PARSE_INACTIVE |
> -                              VIR_DOMAIN_DEF_PARSE_SKIP_VALIDATE;
>              xmlNodePtr domainNode = virXPathNode("./domain", ctxt);
>  
>              VIR_FREE(tmp);
> @@ -309,6 +309,20 @@ virDomainSnapshotDefParse(xmlXPathContextPtr ctxt,
>          } else {
>              VIR_WARN("parsing older snapshot that lacks domain");
>          }
> +
> +        /* /inactiveDomain entry saves the config XML present in a running
> +         * VM. In case of absent, leave parent.inactiveDom NULL and use
> +         * parent.dom for config and live XML. */
> +        if (virXPathString("string(./inactiveDomain/@type)", ctxt)) {

This would leak memory allocated by virXPathString.

> +            xmlNodePtr domainNode = virXPathNode("./inactiveDomain", ctxt);
> +
> +            if (domainNode) {

This doesn't make sense at all. How could it be NULL if you were able to
get its attribute? To solve both issues and also make the code simple,
you can just do

           if ((domainNode = virXPathNode("./inactiveDomain", ctxt))) {
> +                def->parent.inactiveDom = virDomainDefParseNode(ctxt->node->doc, domainNode,
> +                                                                caps, xmlopt, NULL, domainflags);
> +                if (!def->parent.inactiveDom)
> +                    goto cleanup;
> +            }
> +        }
>      } else if (virDomainXMLOptionRunMomentPostParse(xmlopt, &def->parent) < 0) {
>          goto cleanup;
>      }
> @@ -845,6 +859,10 @@ virDomainSnapshotDefFormatInternal(virBufferPtr buf,
>  {
>      size_t i;
>      int domainflags = VIR_DOMAIN_DEF_FORMAT_INACTIVE;
> +    virBuffer inactivedom_buf = VIR_BUFFER_INITIALIZER;
> +    xmlXPathContextPtr inactivedom_ctxt = NULL;
> +    char *inactivedom_str = NULL;
> +    int ret = -1;
>  
>      if (flags & VIR_DOMAIN_SNAPSHOT_FORMAT_SECURE)
>          domainflags |= VIR_DOMAIN_DEF_FORMAT_SECURE;
> @@ -903,6 +921,20 @@ virDomainSnapshotDefFormatInternal(virBufferPtr buf,
>          virBufferAddLit(buf, "</domain>\n");
>      }
>  
> +    if (def->parent.inactiveDom) {
> +        if (virDomainDefFormatInternal(def->parent.inactiveDom, caps,
> +                                       domainflags, &inactivedom_buf, xmlopt) < 0)
> +            goto error;
> +
> +        inactivedom_ctxt = virXPathBuildContext(&inactivedom_buf);
> +        if (!(inactivedom_str = virXPathRenameNode("/domain", "inactiveDomain",
> +                                                   inactivedom_ctxt)))
> +            goto error;

So you format the domain XML, parse it back, rename its root element,
and format it again? Please don't do this. The XML should be formatted
with the right root element right away. And any refactoring allowing you
to do this should be in a separate patch.

> +
> +        virBufferAddStr(buf, inactivedom_str);
> +        virBufferAddLit(buf, "\n");
> +    }
> +
>      if (virSaveCookieFormatBuf(buf, def->cookie,
>                                 virDomainXMLOptionGetSaveCookie(xmlopt)) < 0)
>          goto error;
> @@ -917,11 +949,17 @@ virDomainSnapshotDefFormatInternal(virBufferPtr buf,
>      if (virBufferCheckError(buf) < 0)
>          goto error;
>  
> -    return 0;
> +    ret = 0;
>  
>   error:
> -    virBufferFreeAndReset(buf);
> -    return -1;
> +    VIR_FREE(inactivedom_str);
> +    xmlXPathFreeContext(inactivedom_ctxt);
> +    virBufferFreeAndReset(&inactivedom_buf);
> +
> +    if (ret < 0)
> +        virBufferFreeAndReset(buf);
> +
> +    return ret;
>  }

This hunk should not be needed at all if you format the XML properly.

>  
>  
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 482f915b67..9b95e9b766 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -15697,6 +15697,13 @@ qemuDomainSnapshotCreateXML(virDomainPtr domain,
>                                                          VIR_DOMAIN_DEF_PARSE_SKIP_VALIDATE)))
>              goto endjob;
>  
> +        if (vm->newDef) {
> +            def->parent.inactiveDom = virDomainDefCopy(vm->newDef, caps,
> +                                                       driver->xmlopt, NULL, true);

s/NULL/priv->qemuCaps/ otherwise the event look may end up in a
deadlock.

> +            if (!def->parent.inactiveDom)
> +                goto endjob;
> +        }
> +
>          if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY) {
>              align_location = VIR_DOMAIN_SNAPSHOT_LOCATION_EXTERNAL;
>              align_match = false;
> @@ -16231,6 +16238,7 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>      qemuDomainObjPrivatePtr priv;
>      int rc;
>      virDomainDefPtr config = NULL;
> +    virDomainDefPtr inactiveConfig = NULL;
>      virQEMUDriverConfigPtr cfg = NULL;
>      virCapsPtr caps = NULL;
>      bool was_stopped = false;
> @@ -16331,17 +16339,22 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>           * in the failure cases where we know there was no change?  */
>      }
>  
> -    /* Prepare to copy the snapshot inactive xml as the config of this
> -     * domain.
> -     *
> -     * XXX Should domain snapshots track live xml rather
> -     * than inactive xml?  */
> +    /* Prepare to copy the snapshot inactive domain as the config XML
> +     * and the snapshot domain as the live XML. In case of inactive domain
> +     * NULL, both config and live XML will be copied from snapshot domain.
> +     */
>      if (snap->def->dom) {
>          config = virDomainDefCopy(snap->def->dom, caps,
>                                    driver->xmlopt, NULL, true);

You'll get a conflict here because of recent s/NULL/priv->qemuCaps/

>          if (!config)
>              goto endjob;
>      }
> +    if (snap->def->inactiveDom) {
> +        inactiveConfig = virDomainDefCopy(snap->def->inactiveDom, caps,
> +                                          driver->xmlopt, NULL, true);

s/NULL/priv->qemuCaps/ again.

> +        if (!inactiveConfig)
> +            goto endjob;
> +    }
>  
>      cookie = (qemuDomainSaveCookiePtr) snapdef->cookie;
>  
> @@ -16592,6 +16605,10 @@ qemuDomainRevertToSnapshot(virDomainSnapshotPtr snapshot,
>          goto endjob;
>      }
>  
> +    if (inactiveConfig) {
> +        virDomainDefFree(vm->newDef);
> +        VIR_STEAL_PTR(vm->newDef, inactiveConfig);
> +    }

I think you should be able to use virDomainObjAssignDef here. And even
though it will result in code duplication, I think it should be done
within individual switch branches where appropriate before we send
lifecycle events. And yes, I know qemuDomainRevertToSnapshot is one of
the worst pieces of code we have in libvirt.

>      ret = 0;
>  
>   endjob:

Please drop any changes to virxml.[ch].

Jirka


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