[Qemu-devel] [PATCH 5/5] qmp: add balloon-get-memory-stats & event

[Luiz Capitulino]

This commit adds a QMP API for the guest provided memory statistics
(long disabled by commit 07b0403dfc2b2ac179ae5b48105096cc2d03375a).

The approach taken by the original commit
(625a5befc2e3200b396594f002218d235e375da5) was to extend the
query-balloon command. That approach introduced a severe bug though,
because query-balloon would hang if the guest didn't respond.

The approach taken by this commit is asynchronous and thus avoids
any QMP hangs.

First, a client has to issue the balloon-get-memory-stats command.
That command gets the process started by only sending a request to
the guest. balloon-get-memory-stats doesn't block. When the memory
stats is made available by the guest, it's returned to the client
as an QMP event.

Signed-off-by: Luiz Capitulino <address@hidden>
---
 QMP/qmp-events.txt  |   28 ++++++++++++++++++++++++++++
 balloon.c           |   31 +++++++++++++++++++++++++++++--
 balloon.h           |    4 +++-
 hw/virtio-balloon.c |   39 +++++++++++++++++++++++++++------------
 monitor.c           |    3 +++
 monitor.h           |    1 +
 qapi-schema.json    |   21 +++++++++++++++++++++
 qmp-commands.hx     |    6 ++++++
 8 files changed, 118 insertions(+), 15 deletions(-)

diff --git a/QMP/qmp-events.txt b/QMP/qmp-events.txt
index af586ec..59a5334 100644
--- a/QMP/qmp-events.txt
+++ b/QMP/qmp-events.txt
@@ -1,6 +1,34 @@
                    QEMU Monitor Protocol Events
                    ============================
 
+BALLOON_MEMORY_STATS
+--------------------
+
+Emitted when memory statistics information is made available by the guest.
+
+Data:
+
+- "memory-swapped-in": number of pages swapped in within the guest (json-int)
+- "memory-swapped-out": number of pages swapped out within the guest (json-int)
+- "major-page-faults": number of major page faults within the guest (json-int)
+- "minor-page-faults": number of minor page faults within the guest (json-int)
+- "memory-free": amount of memory (in bytes) free in the guest (json-int)
+- "memory-total": amount of memory (in bytes) visible to the guest (json-int)
+
+Example:
+
+{ "event": "BALLOON_MEMORY_STATS",
+    "data": { "memory-free": 847941632,
+              "major-page-faults": 225,
+              "memory-swapped-in": 0,
+              "minor-page-faults": 222317,
+              "memory-total": 1045516288,
+              "memory-swapped-out": 0 },
+    "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
+
+Note: The balloon-get-memory-stats command must be issued to tell the guest
+      to make memory statistics available.
+
 BLOCK_IO_ERROR
 --------------
 
diff --git a/balloon.c b/balloon.c
index b32b487..0f54d0c 100644
--- a/balloon.c
+++ b/balloon.c
@@ -33,12 +33,15 @@
 
 static QEMUBalloonEvent *balloon_event_fn;
 static QEMUBalloonInfo *balloon_info_fn;
+static QEMUBalloonStats *balloon_stats_fn;
 static void *balloon_opaque;
 
 int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
-                             QEMUBalloonInfo *info_func, void *opaque)
+                             QEMUBalloonInfo *info_func,
+                             QEMUBalloonStats *stats_func, void *opaque)
 {
-    if (balloon_event_fn || balloon_info_fn || balloon_opaque) {
+    if (balloon_event_fn || balloon_info_fn || balloon_stats_fn ||
+        balloon_opaque) {
         /* We're already registered one balloon handler.  How many can
          * a guest really have?
          */
@@ -47,6 +50,7 @@ int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
     }
     balloon_event_fn = event_func;
     balloon_info_fn = info_func;
+    balloon_stats_fn = stats_func;
     balloon_opaque = opaque;
     return 0;
 }
@@ -58,6 +62,7 @@ void qemu_remove_balloon_handler(void *opaque)
     }
     balloon_event_fn = NULL;
     balloon_info_fn = NULL;
+    balloon_stats_fn = NULL;
     balloon_opaque = NULL;
 }
 
@@ -80,6 +85,28 @@ static int qemu_balloon_info(BalloonInfo *info)
     return 1;
 }
 
+static int qemu_balloon_stats(void)
+{
+    if (!balloon_stats_fn) {
+        return 0;
+    }
+    balloon_stats_fn(balloon_opaque);
+    return 1;
+}
+
+void qmp_balloon_get_memory_stats(Error **errp)
+{
+    if (kvm_enabled() && !kvm_has_sync_mmu()) {
+        error_set(errp, QERR_KVM_MISSING_CAP, "synchronous MMU", "balloon");
+        return;
+    }
+
+    if (qemu_balloon_stats() == 0) {
+        error_set(errp, QERR_DEVICE_NOT_ACTIVE, "balloon");
+        return;
+    }
+}
+
 BalloonInfo *qmp_query_balloon(Error **errp)
 {
     BalloonInfo *info;
diff --git a/balloon.h b/balloon.h
index a539354..509e477 100644
--- a/balloon.h
+++ b/balloon.h
@@ -18,9 +18,11 @@
 
 typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
 typedef void (QEMUBalloonInfo)(void *opaque, BalloonInfo *info);
+typedef void (QEMUBalloonStats)(void *opaque);
 
 int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
-                            QEMUBalloonInfo *info_func, void *opaque);
+                            QEMUBalloonInfo *info_func, QEMUBalloonStats 
*stats_func,
+                 void *opaque);
 void qemu_remove_balloon_handler(void *opaque);
 
 #endif
diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index 4307f4c..883d432 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -22,6 +22,8 @@
 #include "virtio-balloon.h"
 #include "kvm.h"
 #include "exec-memory.h"
+#include "monitor.h"
+#include "qemu-objects.h"
 
 #if defined(__linux__)
 #include <sys/mman.h>
@@ -104,8 +106,10 @@ static void virtio_balloon_handle_output(VirtIODevice 
*vdev, VirtQueue *vq)
 static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
+    VirtIOBalloon *dev = s;
     VirtQueueElement *elem = &s->stats_vq_elem;
     VirtIOBalloonStat stat;
+    QObject *stats_obj;
     size_t offset = 0;
 
     if (!virtqueue_pop(vq, elem)) {
@@ -128,6 +132,22 @@ static void virtio_balloon_receive_stats(VirtIODevice 
*vdev, VirtQueue *vq)
             s->stats[tag] = val;
     }
     s->stats_vq_offset = offset;
+
+    stats_obj = qobject_from_jsonf("{ 'memory-swapped-in': %" PRId64 ", "
+                                   "'memory-swapped-out': %" PRId64 ", "
+                                   "'memory-free': %" PRId64 ", "
+                                   "'memory-total': %" PRId64 ", "
+                                   "'major-page-faults': %" PRId64 ", "
+                                   "'minor-page-faults': %" PRId64 " }",
+                                   dev->stats[VIRTIO_BALLOON_S_SWAP_IN],
+                                   dev->stats[VIRTIO_BALLOON_S_SWAP_OUT],
+                                   dev->stats[VIRTIO_BALLOON_S_MEMFREE],
+                                   dev->stats[VIRTIO_BALLOON_S_MEMTOT],
+                                   dev->stats[VIRTIO_BALLOON_S_MAJFLT],
+                                   dev->stats[VIRTIO_BALLOON_S_MINFLT]);
+
+    monitor_protocol_event(QEVENT_BALLOON_STATS, stats_obj);
+    qobject_decref(stats_obj);
 }
 
 static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
@@ -156,31 +176,25 @@ static uint32_t virtio_balloon_get_features(VirtIODevice 
*vdev, uint32_t f)
     return f;
 }
 
-static void virtio_balloon_info(void *opaque, BalloonInfo *info)
+static void virtio_balloon_stats(void *opaque)
 {
     VirtIOBalloon *dev = opaque;
 
-#if 0
-    /* Disable guest-provided stats for now. For more details please check:
-     * https://bugzilla.redhat.com/show_bug.cgi?id=623903
-     *
-     * If you do enable it (which is probably not going to happen as we
-     * need a new command for it), remember that you also need to fill the
-     * appropriate members of the BalloonInfo structure so that the stats
-     * are returned to the client.
-     */
     if (dev->vdev.guest_features & (1 << VIRTIO_BALLOON_F_STATS_VQ)) {
         virtqueue_push(dev->svq, &dev->stats_vq_elem, dev->stats_vq_offset);
         virtio_notify(&dev->vdev, dev->svq);
         return;
     }
-#endif
 
     /* Stats are not supported.  Clear out any stale values that might
      * have been set by a more featureful guest kernel.
      */
     reset_stats(dev);
+}
 
+static void virtio_balloon_info(void *opaque, BalloonInfo *info)
+{
+    VirtIOBalloon *dev = opaque;
     info->actual = ram_size - ((uint64_t) dev->actual <<
                                VIRTIO_BALLOON_PFN_SHIFT);
 }
@@ -236,7 +250,8 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
     s->vdev.get_features = virtio_balloon_get_features;
 
     ret = qemu_add_balloon_handler(virtio_balloon_to_target,
-                                   virtio_balloon_info, s);
+                                   virtio_balloon_info,
+                                   virtio_balloon_stats, s);
     if (ret < 0) {
         virtio_cleanup(&s->vdev);
         return NULL;
diff --git a/monitor.c b/monitor.c
index 7334401..b3d5036 100644
--- a/monitor.c
+++ b/monitor.c
@@ -479,6 +479,9 @@ void monitor_protocol_event(MonitorEvent event, QObject 
*data)
         case QEVENT_SPICE_DISCONNECTED:
             event_name = "SPICE_DISCONNECTED";
             break;
+        case QEVENT_BALLOON_STATS:
+            event_name = "BALLOON_MEMORY_STATS";
+            break;
         default:
             abort();
             break;
diff --git a/monitor.h b/monitor.h
index cfa2f67..a9e7718 100644
--- a/monitor.h
+++ b/monitor.h
@@ -35,6 +35,7 @@ typedef enum MonitorEvent {
     QEVENT_SPICE_CONNECTED,
     QEVENT_SPICE_INITIALIZED,
     QEVENT_SPICE_DISCONNECTED,
+    QEVENT_BALLOON_STATS,
     QEVENT_MAX,
 } MonitorEvent;
 
diff --git a/qapi-schema.json b/qapi-schema.json
index d9b1965..e3b443b 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -1256,3 +1256,24 @@
 { 'command': 'qom-set',
   'data': { 'path': 'str', 'property': 'str', 'value': 'visitor' },
   'gen': 'no' }
+
+##
+# @balloon-get-memory-stats
+#
+# Ask the guest's balloon driver for guest memory statistics.
+#
+# This command will only get the process started and will return immediately.
+# The BALLOON_MEMORY_STATS event will be emitted when the statistics
+# information is returned by the guest.
+#
+# Returns: nothing on success
+#          If the balloon driver is enabled but not functional because the KVM
+#          kernel module cannot support it, KvmMissingCap
+#          If no balloon device is present, DeviceNotActive
+#
+# Notes: There's no guarantees the guest will ever respond, thus the
+#        BALLOON_MEMORY_STATS event may never be emitted.
+#
+# Since: 1.1
+##
+{ 'command': 'balloon-get-memory-stats' }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 7e3f4b9..7a80cda 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -2027,3 +2027,9 @@ EQMP
        .args_type  = "path:s,property:s",
        .mhandler.cmd_new = qmp_qom_get,
     },
+
+    {
+        .name       = "balloon-get-memory-stats",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_balloon_get_memory_stats,
+    },
-- 
1.7.9.rc0.dirty