block: BLOCK_IO_ERROR QMP event

This commit introduces the bdrv_mon_event() function, which
should be called by block subsystems (eg. IDE) when a I/O
error occurs, so that an QMP event is emitted.

The following information is currently provided in the event:

- device name
- operation (ie. "read" or "write")
- action taken (eg. "stop")

Event example:

{ "event": "BLOCK_IO_ERROR",
    "data": { "device": "ide0-hd1",
              "operation": "write",
              "action": "stop" },
    "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

block.c

@@ -1170,6 +1170,35 @@ int bdrv_is_allocated(BlockDriverState *bs, int64_t sector_num, int nb_sectors,
     return bs->drv->bdrv_is_allocated(bs, sector_num, nb_sectors, pnum);
 }
 
+void bdrv_mon_event(const BlockDriverState *bdrv,
+                    BlockMonEventAction action, int is_read)
+{
+    QObject *data;
+    const char *action_str;
+
+    switch (action) {
+    case BDRV_ACTION_REPORT:
+        action_str = "report";
+        break;
+    case BDRV_ACTION_IGNORE:
+        action_str = "ignore";
+        break;
+    case BDRV_ACTION_STOP:
+        action_str = "stop";
+        break;
+    default:
+        abort();
+    }
+
+    data = qobject_from_jsonf("{ 'device': %s, 'action': %s, 'operation': %s }",
+                              bdrv->device_name,
+                              action_str,
+                              is_read ? "read" : "write");
+    monitor_protocol_event(QEVENT_BLOCK_IO_ERROR, data);
+
+    qobject_decref(data);
+}
+
 static void bdrv_print_dict(QObject *obj, void *opaque)
 {
     QDict *bs_dict;

block.h

@@ -44,6 +44,12 @@ typedef struct QEMUSnapshotInfo {
 #define BDRV_SECTOR_SIZE   (1 << BDRV_SECTOR_BITS)
 #define BDRV_SECTOR_MASK   ~(BDRV_SECTOR_SIZE - 1);
 
+typedef enum {
+    BDRV_ACTION_REPORT, BDRV_ACTION_IGNORE, BDRV_ACTION_STOP
+} BlockMonEventAction;
+
+void bdrv_mon_event(const BlockDriverState *bdrv,
+                    BlockMonEventAction action, int is_read);
 void bdrv_info_print(Monitor *mon, const QObject *data);
 void bdrv_info(Monitor *mon, QObject **ret_data);
 void bdrv_stats_print(Monitor *mon, const QObject *data);