From b70bc3fb7517fe18b7ef6d2c3801c3b217f977bb Mon Sep 17 00:00:00 2001
Message-Id: <b70bc3fb7517fe18b7ef6d2c3801c3b217f977bb@dist-git>
From: Jiri Denemark <jdenemar@redhat.com>
Date: Thu, 2 Jul 2015 22:32:54 +0200
Subject: [PATCH] qemu: Don't report false error from MigrateFinish

virDomainMigrateFinish* APIs were unfortunately designed to return the
pointer to the domain on destination and NULL on error. This looks OK in
normal cases but the same API is also called when we know migration
failed and thus we expect Finish to return NULL even if it actually did
all it was supposed to do without any error. The call is defined to
return nonnull domain pointer over RPC, which means returning NULL will
always result in an error being send. If this was not in fact an error,
the API itself wouldn't set anything to the thread local virError, which
makes the RPC layer come up with it's own "Library function returned
error but did not set virError" error.

This is quite confusing and also hard to detect by the caller. This
patch adds a special error code which can be used to check that Finish
successfully aborted migration.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
(cherry picked from commit 44c42b564dc61ddc8fdfc5b6ca4ca969bcffc7d8)

https://bugzilla.redhat.com/show_bug.cgi?id=1090093

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
---
 include/libvirt/virterror.h | 1 +
 src/qemu/qemu_migration.c   | 6 ++++++
 src/util/virerror.c         | 3 +++
 3 files changed, 10 insertions(+)

diff --git a/include/libvirt/virterror.h b/include/libvirt/virterror.h
index 6325030..f716cb9 100644
--- a/include/libvirt/virterror.h
+++ b/include/libvirt/virterror.h
@@ -307,6 +307,7 @@ typedef enum {
     VIR_ERR_CPU_INCOMPATIBLE = 91,      /* given CPU is incompatible with host
                                            CPU*/
     VIR_ERR_XML_INVALID_SCHEMA = 92,    /* XML document doesn't validate against schema */
+    VIR_ERR_MIGRATE_FINISH_OK = 93,     /* Finish API succeeded but it is expected to return NULL */
 } virErrorNumber;
 
 /**
diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
index 58874ee..a9cbada 100644
--- a/src/qemu/qemu_migration.c
+++ b/src/qemu/qemu_migration.c
@@ -5751,6 +5751,12 @@ qemuMigrationFinish(virQEMUDriverPtr driver,
     }
     virObjectUnref(caps);
     virObjectUnref(cfg);
+
+    /* Set a special error if Finish is expected to return NULL as a result of
+     * successful call with retcode != 0
+     */
+    if (retcode != 0 && !dom && !virGetLastError())
+        virReportError(VIR_ERR_MIGRATE_FINISH_OK, NULL);
     return dom;
 }
 
diff --git a/src/util/virerror.c b/src/util/virerror.c
index 60b2e79..6dc05f4 100644
--- a/src/util/virerror.c
+++ b/src/util/virerror.c
@@ -1369,6 +1369,9 @@ virErrorMsg(virErrorNumber error, const char *info)
             else
                 errmsg = _("XML document failed to validate against schema: %s");
             break;
+        case VIR_ERR_MIGRATE_FINISH_OK:
+            errmsg = _("migration successfully aborted");
+            break;
     }
     return errmsg;
 }
-- 
2.4.5