[PATCH] qemu: blockjob: Avoid spurious log errors when cancelling a shallow copy with reused images

[Peter Krempa]

In case when a user starts a block copy operation with
VIR_DOMAIN_BLOCK_COPY_SHALLOW and VIR_DOMAIN_BLOCK_COPY_REUSE_EXT and
both the reused image and the original disk have a backing image libvirt
specifically does not insert the backing image until after the job is
asked to be completed via virBlockJobAbort with
VIR_DOMAIN_BLOCK_JOB_ABORT_PIVOT.

This is so that management applications can copy the backing image on
the background.

Now when a user aborts the block job instead of cancelling it we'd
ignore the fact that we didn't insert the backing image yet and the
cancellation would result into a 'blockdev-del' of a invalid node name
and thus an 'error' severity entry in the log.

To solve this issue we use the same conditions when the backing image
addition is avoided to remove the internal state for them prior to the
call to unplug the mirror destination.

Reported-by: Kashyap Chamarthy <kchamart at redhat.com>
Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 src/qemu/qemu_blockjob.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/src/qemu/qemu_blockjob.c b/src/qemu/qemu_blockjob.c
index 726df95067..2442865b9b 100644
--- a/src/qemu/qemu_blockjob.c
+++ b/src/qemu/qemu_blockjob.c
@@ -1406,6 +1406,8 @@ qemuBlockJobProcessEventConcludedCopyAbort(virQEMUDriver *driver,
                                            qemuBlockJobData *job,
                                            qemuDomainAsyncJob asyncJob)
 {
+    qemuDomainObjPrivate *priv = vm->privateData;
+
     VIR_DEBUG("copy job '%s' on VM '%s' aborted", job->name, vm->def->name);

     /* mirror may be NULL for copy job corresponding to migration */
@@ -1413,6 +1415,21 @@ qemuBlockJobProcessEventConcludedCopyAbort(virQEMUDriver *driver,
         !job->disk->mirror)
         return;

+    if (!job->jobflagsmissing) {
+        bool shallow = job->jobflags & VIR_DOMAIN_BLOCK_COPY_SHALLOW;
+        bool reuse = job->jobflags & VIR_DOMAIN_BLOCK_COPY_REUSE_EXT;
+
+        /* In the special case of a shallow copy with reused image we don't
+         * hotplug the full chain when QEMU_CAPS_BLOCKDEV_SNAPSHOT_ALLOW_WRITE_ONLY
+         * is supported. Attempting to delete it would thus result in spurious
+         * errors as we'd attempt to blockdev-del images which were not added
+         * yet */
+        if (reuse && shallow &&
+            virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_BLOCKDEV_SNAPSHOT_ALLOW_WRITE_ONLY) &&
+            virStorageSourceHasBacking(job->disk->mirror))
+            g_clear_pointer(&job->disk->mirror->backingStore, virObjectUnref);
+    }
+
     /* activeWrite bitmap is removed automatically here */
     qemuBlockJobEventProcessConcludedRemoveChain(driver, vm, asyncJob, job->disk->mirror);
     g_clear_pointer(&job->disk->mirror, virObjectUnref);
-- 
2.35.1