From f78e7381ac369952197ffb23b02f56ee430214e7 Mon Sep 17 00:00:00 2001
Message-Id: <f78e7381ac369952197ffb23b02f56ee430214e7@dist-git>
From: Eric Blake <eblake@redhat.com>
Date: Thu, 21 Aug 2014 16:07:30 -0600
Subject: [PATCH] qemu: reject rather than hang on blockcommit of active layer

7.0.z: https://bugzilla.redhat.com/show_bug.cgi?id=1150379
7.1: https://bugzilla.redhat.com/show_bug.cgi?id=1062142

qemu 2.0 added the ability to commit the active layer, but slightly
differently than what libvirt had been anticipating in its
implementation of the virDomainBlockCommit call.  As a result, if
you attempt to do a 'virsh blockcommit $dom vda', qemu gets into a
state where it is waiting on libvirt to end the job, while libvirt
is waiting on qemu to end the job, and the guest is effectively
hung with regards to further commands for that block device.

I have patches coming down the pipeline that will add full support
for blockcommit of the active layer when coupled with qemu 2.0 or
later; but they depend on Peter's improvements to block job handling
and form enough of a new feature that they are not ready for
inclusion in the 1.2.5 release.  So for now, just reject the
attempt, rather than letting the user get stuck.  This is no worse
than the behavior of qemu 1.7 rejecting the job.

* src/qemu/qemu_driver.c (qemuDomainBlockCommit): Reject active
commit.

Signed-off-by: Eric Blake <eblake@redhat.com>
(cherry picked from commit e6bcbcd32c70ae394e7b6a530012fe8b07a59b5d)

Conflicts:
	src/qemu/qemu_driver.c - no refactoring of virStorageFileChainLookup
Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
---
 src/qemu/qemu_driver.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 72d03b5..1ce4c39 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -15312,6 +15312,16 @@ qemuDomainBlockCommit(virDomainPtr dom, const char *path, const char *base,
                        top, path);
         goto endjob;
     }
+
+    /* FIXME: qemu 2.0 supports active commit, but as a two-stage
+     * process; qemu 2.1 is further improving active commit. We need
+     * to start supporting it in libvirt. */
+    if (top_meta == disk->backingChain) {
+        virReportError(VIR_ERR_OPERATION_UNSUPPORTED, "%s",
+                       _("committing the active layer not supported yet"));
+        goto endjob;
+    }
+
     if (!top_meta || !top_meta->backingStore) {
         virReportError(VIR_ERR_INVALID_ARG,
                        _("top '%s' in chain for '%s' has no backing file"),
-- 
2.2.0