[libvirt PATCH v2 09/10] qemu: block: add external snapshot-delete top-level algorithm

[Pavel Mores]

This uses the helpers introduced in previous three commits and assembles
the top-level snapshot deletion algorithm in their terms.

Note that the third phase - waiting for blockcommits to finish - is
conceptually optional and a flag/parameter might be exposed to the user in
the future to skip the third phase.  This would make the whole operation
asynchronous and let the user deal with concluding the blockcommits
manually, using the generic blockjob tools.

Signed-off-by: Pavel Mores <pmores at redhat.com>
---
 src/libvirt_private.syms |  1 +
 src/qemu/qemu_driver.c   | 64 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index 935ef7303b..f68eb500ec 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1049,6 +1049,7 @@ virDomainListCheckpoints;
 # conf/virdomainmomentobjlist.h
 virDomainMomentDropChildren;
 virDomainMomentDropParent;
+virDomainMomentFindLeaf;
 virDomainMomentForEachChild;
 virDomainMomentForEachDescendant;
 virDomainMomentMoveChildren;
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index a2629e9002..57e81e3720 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -17000,6 +17000,70 @@ qemuDomainSnapshotDeleteExternalWaitForJobs(virDomainObjPtr vm,
 }
 
 
+static int
+qemuDomainSnapshotDeleteExternal(virDomainObjPtr vm,
+                                 virQEMUDriverPtr driver,
+                                 virDomainMomentObjPtr snap,
+                                 unsigned int flags)
+{
+    /* TODO Apr 29, 2020: ultimately, use 'flags' to set this.  Until that
+     * is supported, just run always synchronously. */
+    bool async = false;
+    virDomainSnapshotDefPtr snapdef = virDomainSnapshotObjGetDef(snap);
+    virDomainMomentObjPtr leaf = snap->nchildren ? virDomainMomentFindLeaf(snap) : snap;
+    virDomainMomentObjPtr parent = snap->parent;
+    g_autofree virBlockCommitDesc *blockCommitDescs = NULL;
+    int numBlockCommits = snapdef->ndisks;
+
+    /* This function only works if the chain below 'snap' is linear.  If
+     * there's no unique leaf it means the chain of 'snap's children
+     * branches at some point.  Also, if there *is* a leaf but it's not
+     * the current snapshot, bail out as well. */
+    if (leaf == NULL) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("can't delete '%s', snapshot chain branches"),
+                       snapdef->parent.name);
+        return -1;
+    }
+    if (leaf != virDomainSnapshotGetCurrent(vm->snapshots)) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("can't delete '%s', leaf snapshot is not current"),
+                       snapdef->parent.name);
+        return -1;
+    }
+    if (parent->nchildren > 1) {
+        /* TODO 'snap's parent has multiple children, meaning it's a
+         * branching point in snapshot tree.  This means we can't
+         * delete 'snap' by commiting into its parent as doing so would
+         * corrupt the other branches rooted in the parent.  We might
+         * still be able to delete 'snap' though by pulling into its
+         * child/children. */
+
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
+                       _("can't delete %s, its parent has multiple children"),
+                       snapdef->parent.name);
+        return -1;
+    }
+
+    if (!virDomainObjIsActive(vm))
+        return -1;
+
+    blockCommitDescs = qemuDomainSnapshotDeleteExternalGetJobDescriptors(vm, snap, flags);
+    if (blockCommitDescs == NULL)
+        return -1;
+
+    if (qemuDomainSnapshotDeleteExternalLaunchJobs(vm, driver, blockCommitDescs, numBlockCommits) < 0)
+        return -1;
+
+    if (!async) {
+        if (qemuDomainSnapshotDeleteExternalWaitForJobs(vm, driver, blockCommitDescs, numBlockCommits) < 0)
+            return -1;
+    }
+
+    return 0;
+}
+
+
 static int
 qemuDomainSnapshotDelete(virDomainSnapshotPtr snapshot,
                          unsigned int flags)
-- 
2.24.1