snapshot: new query APIs

Right now, starting from just a virDomainSnapshotPtr, and wanting to
know if it is the current snapshot for its respective domain, you have
to use virDomainSnapshotGetDomain(), then virDomainSnapshotCurrent(),
then compare the two names returned by virDomainSnapshotGetName().
It is a bit easier if we can directly query this information from the
snapshot itself.

Right now, it is possible to filter a snapshot listing based on
whether snapshots have metadata that would prevent domain deletion,
but the only way to learn if an individual snapshot has metadata is
to see if that snapshot appears in the list returned by a listing.
Additionally, I hope to expand the qemu driver in a future patch to
use qemu-img to reconstruct snapshot XML corresponding to internal
qcow2 snapshot names not otherwise tracked by libvirt (in part, so
that libvirt can guarantee that new snapshots are not created with
a name that would silently corrupt the existing portion of the qcow2
file); if I ever get that in, then it would no longer be an all-or-none
decision on whether snapshots have metadata, and becomes all the more
important to be able to directly determine that information from a
particular snapshot.

Other query functions (such as virDomainIsActive) do not have a flags
argument, but since virDomainHasCurrentSnapshot takes a flags argument,
I figured it was safer to provide a flags argument here as well.

* include/libvirt/libvirt.h.in (virDomainSnapshotIsCurrent)
(virDomainSnapshotHasMetadata): New declarations.
* src/libvirt.c (virDomainSnapshotIsCurrent)
(virDomainSnapshotHasMetadata): New functions.
* src/libvirt_public.syms (LIBVIRT_0.9.13): Export them.
* src/driver.h (virDrvDomainSnapshotIsCurrent)
(virDrvDomainSnapshotHasMetadata): New driver callbacks.

include/libvirt/libvirt.h.in

@@ -3401,6 +3401,15 @@ virDomainSnapshotPtr virDomainSnapshotCurrent(virDomainPtr domain,
 virDomainSnapshotPtr virDomainSnapshotGetParent(virDomainSnapshotPtr snapshot,
                                                 unsigned int flags);
 
+/* Determine if a snapshot is the current snapshot of its domain.  */
+int virDomainSnapshotIsCurrent(virDomainSnapshotPtr snapshot,
+                               unsigned int flags);
+
+/* Determine if a snapshot has associated libvirt metadata that would
+ * prevent the deletion of its domain.  */
+int virDomainSnapshotHasMetadata(virDomainSnapshotPtr snapshot,
+                                 unsigned int flags);
+
 typedef enum {
     VIR_DOMAIN_SNAPSHOT_REVERT_RUNNING = 1 << 0, /* Run after revert */
     VIR_DOMAIN_SNAPSHOT_REVERT_PAUSED  = 1 << 1, /* Pause after revert */

src/driver.h

@@ -649,6 +649,14 @@ typedef virDomainSnapshotPtr
     (*virDrvDomainSnapshotCurrent)(virDomainPtr domain,
                                    unsigned int flags);
 
+typedef int
+    (*virDrvDomainSnapshotIsCurrent)(virDomainSnapshotPtr snapshot,
+                                     unsigned int flags);
+
+typedef int
+    (*virDrvDomainSnapshotHasMetadata)(virDomainSnapshotPtr snapshot,
+                                       unsigned int flags);
+
 typedef int
     (*virDrvDomainRevertToSnapshot)(virDomainSnapshotPtr snapshot,
                                     unsigned int flags);
@@ -986,6 +994,8 @@ struct _virDriver {
     virDrvDomainHasCurrentSnapshot domainHasCurrentSnapshot;
     virDrvDomainSnapshotGetParent domainSnapshotGetParent;
     virDrvDomainSnapshotCurrent domainSnapshotCurrent;
+    virDrvDomainSnapshotIsCurrent domainSnapshotIsCurrent;
+    virDrvDomainSnapshotHasMetadata domainSnapshotHasMetadata;
     virDrvDomainRevertToSnapshot domainRevertToSnapshot;
     virDrvDomainSnapshotDelete domainSnapshotDelete;
     virDrvDomainQemuMonitorCommand qemuDomainMonitorCommand;

src/libvirt.c

@@ -17330,6 +17330,91 @@ error:
     return NULL;
 }
 
+/**
+ * virDomainSnapshotIsCurrent:
+ * @snapshot: a snapshot object
+ * @flags: extra flags; not used yet, so callers should always pass 0
+ *
+ * Determine if the given snapshot is the domain's current snapshot.  See
+ * also virDomainHasCurrentSnapshot().
+ *
+ * Returns 1 if current, 0 if not current, or -1 on error.
+ */
+int virDomainSnapshotIsCurrent(virDomainSnapshotPtr snapshot,
+                               unsigned int flags)
+{
+    virConnectPtr conn;
+
+    VIR_DEBUG("snapshot=%p, flags=%x", snapshot, flags);
+
+    virResetLastError();
+
+    if (!VIR_IS_DOMAIN_SNAPSHOT(snapshot)) {
+        virLibDomainSnapshotError(VIR_ERR_INVALID_DOMAIN_SNAPSHOT,
+                                  __FUNCTION__);
+        virDispatchError(NULL);
+        return -1;
+    }
+
+    conn = snapshot->domain->conn;
+
+    if (conn->driver->domainSnapshotIsCurrent) {
+        int ret;
+        ret = conn->driver->domainSnapshotIsCurrent(snapshot, flags);
+        if (ret < 0)
+            goto error;
+        return ret;
+    }
+
+    virLibConnError(VIR_ERR_NO_SUPPORT, __FUNCTION__);
+error:
+    virDispatchError(conn);
+    return -1;
+}
+
+/**
+ * virDomainSnapshotHasMetadata:
+ * @snapshot: a snapshot object
+ * @flags: extra flags; not used yet, so callers should always pass 0
+ *
+ * Determine if the given snapshot is associated with libvirt metadata
+ * that would prevent the deletion of the domain.
+ *
+ * Returns 1 if the snapshot has metadata, 0 if the snapshot exists without
+ * help from libvirt, or -1 on error.
+ */
+int virDomainSnapshotHasMetadata(virDomainSnapshotPtr snapshot,
+                                 unsigned int flags)
+{
+    virConnectPtr conn;
+
+    VIR_DEBUG("snapshot=%p, flags=%x", snapshot, flags);
+
+    virResetLastError();
+
+    if (!VIR_IS_DOMAIN_SNAPSHOT(snapshot)) {
+        virLibDomainSnapshotError(VIR_ERR_INVALID_DOMAIN_SNAPSHOT,
+                                  __FUNCTION__);
+        virDispatchError(NULL);
+        return -1;
+    }
+
+    conn = snapshot->domain->conn;
+
+    if (conn->driver->domainSnapshotHasMetadata) {
+        int ret;
+        ret = conn->driver->domainSnapshotHasMetadata(snapshot, flags);
+        if (ret < 0)
+            goto error;
+        return ret;
+    }
+
+    virLibConnError(VIR_ERR_NO_SUPPORT, __FUNCTION__);
+error:
+    virDispatchError(conn);
+    return -1;
+}
+
 /**
  * virDomainRevertToSnapshot:
  * @snapshot: a domain snapshot object

src/libvirt_public.syms

@@ -536,6 +536,8 @@ LIBVIRT_0.9.11 {
 
 LIBVIRT_0.9.13 {
     global:
+        virDomainSnapshotHasMetadata;
+        virDomainSnapshotIsCurrent;
         virDomainSnapshotRef;
 } LIBVIRT_0.9.11;