Introduce VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT

https://bugzilla.redhat.com/show_bug.cgi?id=1552092

If there's a long running job it might cause us to wait 30
seconds before we give up acquiring the job. This is problematic
to interactive applications that fetch stats repeatedly every few
seconds.

The solution is to introduce
VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT flag which tries to
acquire job but does not wait if acquiring failed.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

include/libvirt/libvirt-domain.h

@@ -2055,6 +2055,8 @@ typedef enum {
     VIR_CONNECT_GET_ALL_DOMAINS_STATS_SHUTOFF = VIR_CONNECT_LIST_DOMAINS_SHUTOFF,
     VIR_CONNECT_GET_ALL_DOMAINS_STATS_OTHER = VIR_CONNECT_LIST_DOMAINS_OTHER,
 
+    VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT = 1 << 29, /* report statistics that can be obtained
+                                                           immediately without any blocking */
     VIR_CONNECT_GET_ALL_DOMAINS_STATS_BACKING = 1 << 30, /* include backing chain for block stats */
     VIR_CONNECT_GET_ALL_DOMAINS_STATS_ENFORCE_STATS = 1U << 31, /* enforce requested stats */
 } virConnectGetAllDomainStatsFlags;

src/libvirt-domain.c

@@ -11502,6 +11502,12 @@ virConnectGetDomainCapabilities(virConnectPtr conn,
  * fields for offline domains if the statistics are meaningful only for a
  * running domain.
  *
+ * Passing VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT in
+ * @flags means when libvirt is unable to fetch stats for any of
+ * the domains (for whatever reason) only a subset of statistics
+ * is returned for the domain.  That subset being statistics that
+ * don't involve querying the underlying hypervisor.
+ *
  * Similarly to virConnectListAllDomains, @flags can contain various flags to
  * filter the list of domains to provide stats for.
  *
@@ -11586,6 +11592,12 @@ virConnectGetAllDomainStats(virConnectPtr conn,
  * fields for offline domains if the statistics are meaningful only for a
  * running domain.
  *
+ * Passing VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT in
+ * @flags means when libvirt is unable to fetch stats for any of
+ * the domains (for whatever reason) only a subset of statistics
+ * is returned for the domain.  That subset being statistics that
+ * don't involve querying the underlying hypervisor.
+ *
  * Note that any of the domain list filtering flags in @flags may be rejected
  * by this function.
  *

src/qemu/qemu_driver.c

@@ -20426,6 +20426,7 @@ qemuConnectGetAllDomainStats(virConnectPtr conn,
     virCheckFlags(VIR_CONNECT_LIST_DOMAINS_FILTERS_ACTIVE |
                   VIR_CONNECT_LIST_DOMAINS_FILTERS_PERSISTENT |
                   VIR_CONNECT_LIST_DOMAINS_FILTERS_STATE |
+                  VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT |
                   VIR_CONNECT_GET_ALL_DOMAINS_STATS_BACKING |
                   VIR_CONNECT_GET_ALL_DOMAINS_STATS_ENFORCE_STATS, -1);
 
@@ -20460,9 +20461,17 @@ qemuConnectGetAllDomainStats(virConnectPtr conn,
 
         virObjectLock(vm);
 
-        if (HAVE_JOB(privflags) &&
-            qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY) == 0)
-            domflags |= QEMU_DOMAIN_STATS_HAVE_JOB;
+        if (HAVE_JOB(privflags)) {
+            int rv;
+
+            if (flags & VIR_CONNECT_GET_ALL_DOMAINS_STATS_NOWAIT)
+                rv = qemuDomainObjBeginJobNowait(driver, vm, QEMU_JOB_QUERY);
+            else
+                rv = qemuDomainObjBeginJob(driver, vm, QEMU_JOB_QUERY);
+
+            if (rv == 0)
+                domflags |= QEMU_DOMAIN_STATS_HAVE_JOB;
+        }
         /* else: without a job it's still possible to gather some data */
 
         if (flags & VIR_CONNECT_GET_ALL_DOMAINS_STATS_BACKING)