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Re: [libvirt] [PATCH 3/4] snapshot: expose location through virsh snapshot-info



On 11/14/2012 11:43 AM, Eric Blake wrote:
>> Bleah. Raw XML parsing. Wouldn't it be easier in and cleaner convert
>> this piece code to use the XML parser and xpath?
> 
> Not the first time we've done this.  I agree that using the XML parser
> and xpath is probably nicer, but it actually takes more code than a
> simple strstr.
> 
>> The code looks OK in what it should be doing, but I don't like the raw
>> XML parse-hacking stuff. The only reason to put this in as-is would be
>> if it would be really complicated/overheading to use xpath here.
> 
> I'll post an interdiff that shows what it would take to use xpath, and
> we can decide based on how nice or ugly it looks.

Here's the diff; any decisions on whether to go with xpath?

 tools/virsh-snapshot.c | 61
+++++++++++++++++++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 21 deletions(-)

diff --git i/tools/virsh-snapshot.c w/tools/virsh-snapshot.c
index e38ce84..36f5b46 100644
--- i/tools/virsh-snapshot.c
+++ w/tools/virsh-snapshot.c
@@ -797,8 +797,10 @@ cmdSnapshotInfo(vshControl *ctl, const vshCmd *cmd)
     virDomainSnapshotPtr snapshot = NULL;
     const char *name;
     char *doc = NULL;
-    char *state;
-    bool internal;
+    xmlDocPtr xmldoc = NULL;
+    xmlXPathContextPtr ctxt = NULL;
+    char *state = NULL;
+    int external;
     char *parent = NULL;
     bool ret = false;
     int count;
@@ -840,39 +842,48 @@ cmdSnapshotInfo(vshControl *ctl, const vshCmd *cmd)
     if (!doc)
         goto cleanup;

-    state = strstr(doc, "<state>");
+    xmldoc = virXMLParseStringCtxt(doc, _("(domain_snapshot)"), &ctxt);
+    if (!xmldoc)
+        goto cleanup;
+
+    state = virXPathString("string(/domainsnapshot/state)", ctxt);
     if (!state) {
         vshError(ctl, "%s",
                  _("unexpected problem reading snapshot xml"));
         goto cleanup;
     }
-    state += strlen("<state>");
-    vshPrint(ctl, "%-15s %.*s\n", _("State:"),
-             (int) (strchr(state, '<') - state), state);
+    vshPrint(ctl, "%-15s %s\n", _("State:"), state);

     /* In addition to state, location is useful.  If the snapshot has
      * a <memory> element, then the existence of snapshot='external'
      * prior to <domain> is the deciding factor; for snapshots
      * created prior to 1.0.1, a state of disk-only is the only
      * external snapshot.  */
-    if (strstr(state, "<memory")) {
-        char *domain = strstr(state, "<domain");
+    switch (virXPathBoolean("boolean(/domainsnapshot/memory)", ctxt)) {
+    case 1:
+        external =
virXPathBoolean("boolean(/domainsnapshot/memory/@snapshot=external "
+                                   "|
/domainsnapshot/disks/disk/@snapshot=external)",
+                                   ctxt);
+        break;
+    case 0:
+        external = STREQ(state, "disk-snapshot");
+        break;
+    default:
+        external = -1;
+        break;

-        if (!domain) {
-            vshError(ctl, "%s",
-                     _("unexpected problem reading snapshot xml"));
-            goto cleanup;
-        }
-        internal = !memmem(state, domain - state, "snapshot='external'",
-                           strlen("snapshot='external'"));
-    } else {
-        internal = !STRPREFIX(state, "disk-snapshot");
+    }
+    if (external < 0) {
+        vshError(ctl, "%s",
+                 _("unexpected problem reading snapshot xml"));
+        goto cleanup;
     }
     vshPrint(ctl, "%-15s %s\n", _("Location:"),
-             internal ? _("internal") : _("external"));
+             external ? _("external") : _("internal"));

-    if (vshGetSnapshotParent(ctl, snapshot, &parent) < 0)
-        goto cleanup;
+    /* Since we already have the XML, there's no need to call
+     * virDomainSnapshotGetParent */
+    parent = virXPathString("string(/domainsnapshot/parent/name)", ctxt);
     vshPrint(ctl, "%-15s %s\n", _("Parent:"), parent ? parent : "-");

     /* Children, Descendants.  After this point, the fallback to
@@ -884,8 +895,13 @@ cmdSnapshotInfo(vshControl *ctl, const vshCmd *cmd)
     }
     flags = 0;
     count = virDomainSnapshotNumChildren(snapshot, flags);
-    if (count < 0)
+    if (count < 0) {
+        if (last_error->code == VIR_ERR_NO_SUPPORT) {
+            vshResetLibvirtError();
+            ret = true;
+        }
         goto cleanup;
+    }
     vshPrint(ctl, "%-15s %d\n", _("Children:"), count);
     flags = VIR_DOMAIN_SNAPSHOT_LIST_DESCENDANTS;
     count = virDomainSnapshotNumChildren(snapshot, flags);
@@ -908,6 +924,9 @@ cmdSnapshotInfo(vshControl *ctl, const vshCmd *cmd)
     ret = true;

 cleanup:
+    VIR_FREE(state);
+    xmlXPathFreeContext(ctxt);
+    xmlFreeDoc(xmldoc);
     VIR_FREE(doc);
     VIR_FREE(parent);
     if (snapshot)

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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