[libvirt] [PATCH 2/3] qemu: special error code in case of no job on cancel block job

[Nikolay Shirokovskiy]

Special error code helps gracefully handle race conditions on
blockjob cancelling. Consider for example pull backup. We want
to stop it and in the process we cancel blockjob for some of the
exported disks. But at the time this command reaches qemu blockjob
fail for some reason and cancel result and result of stopping
will be an error with quite unexpecte message - no such job (sort of).
Instead we can detect this race and treat as correct cancelling
and wait until fail event will arrive. Then we can report corect
error message with some details from qemu probably.

Users of domainBlockJobAbort can be affected as -2 is new possible
return code. Not sure if I should stick to the original behaviour in
this case.
---
 src/qemu/qemu_monitor.c      |  5 +++++
 src/qemu/qemu_monitor_json.c | 11 +++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_monitor.c b/src/qemu/qemu_monitor.c
index 4171914..944856d 100644
--- a/src/qemu/qemu_monitor.c
+++ b/src/qemu/qemu_monitor.c
@@ -3335,6 +3335,11 @@ qemuMonitorBlockStream(qemuMonitorPtr mon,
 }
 
 
+/* return:
+ *  0 in case of success
+ * -1 in case of general error
+ * -2 in case there is no such job
+ */
 int
 qemuMonitorBlockJobCancel(qemuMonitorPtr mon,
                           const char *device,
diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index 7903b47..42b05c4 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/src/qemu/qemu_monitor_json.c
@@ -4351,6 +4351,7 @@ qemuMonitorJSONBlockJobError(virJSONValuePtr reply,
     if (qemuMonitorJSONErrorIsClass(error, "DeviceNotActive")) {
         virReportError(VIR_ERR_OPERATION_INVALID,
                        _("No active operation on device: %s"), device);
+        return -2;
     } else if (qemuMonitorJSONErrorIsClass(error, "DeviceInUse")) {
         virReportError(VIR_ERR_OPERATION_FAILED,
                        _("Device %s in use"), device);
@@ -4408,6 +4409,11 @@ qemuMonitorJSONBlockStream(qemuMonitorPtr mon,
 }
 
 
+/* return:
+ *  0 in case of success
+ * -1 in case of general error
+ * -2 in case there is no such job
+ */
 int
 qemuMonitorJSONBlockJobCancel(qemuMonitorPtr mon,
                               const char *device,
@@ -4426,10 +4432,7 @@ qemuMonitorJSONBlockJobCancel(qemuMonitorPtr mon,
     if (qemuMonitorJSONCommand(mon, cmd, &reply) < 0)
         goto cleanup;
 
-    if (qemuMonitorJSONBlockJobError(reply, cmd_name, device) < 0)
-        goto cleanup;
-
-    ret = 0;
+    ret = qemuMonitorJSONBlockJobError(reply, cmd_name, device);
 
  cleanup:
     virJSONValueFree(cmd);
-- 
1.8.3.1