qemu: Refactor parsing of block device IO tuning parameters.

This patch refactors the JSON parsing function that extracts the block
IO tuning parameters from qemu's output. The most impacting change
concerns the error message that is returned if the reply from qemu does
not contain the needed data. The data for IO parameter tuning were added
in qemu 1.1 and the previous error message was confusing.

This patch also breaks long lines and extracts a multiple time used code
pattern to a macro.

src/qemu/qemu_monitor_json.c

@@ -3648,6 +3648,16 @@ int qemuMonitorJSONOpenGraphics(qemuMonitorPtr mon,
 }
 
 
+#define GET_THROTTLE_STATS(FIELD, STORE)                                      \
+    if (virJSONValueObjectGetNumberUlong(inserted,                            \
+                                         FIELD,                               \
+                                         &reply->STORE) < 0) {                \
+        virReportError(VIR_ERR_INTERNAL_ERROR,                                \
+                       _("block_io_throttle field '%s' missing "              \
+                         "in qemu's output"),                                 \
+                       #STORE);                                               \
+            goto cleanup;                                                     \
+    }
 static int
 qemuMonitorJSONBlockIoThrottleInfo(virJSONValuePtr result,
                                    const char *device,
@@ -3656,7 +3666,7 @@ qemuMonitorJSONBlockIoThrottleInfo(virJSONValuePtr result,
     virJSONValuePtr io_throttle;
     int ret = -1;
     int i;
-    int found = 0;
+    bool found = false;
 
     io_throttle = virJSONValueObjectGet(result, "return");
 
@@ -3673,13 +3683,15 @@ qemuMonitorJSONBlockIoThrottleInfo(virJSONValuePtr result,
 
         if (!temp_dev || temp_dev->type != VIR_JSON_TYPE_OBJECT) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("block_io_throttle device entry was not in expected format"));
+                           _("block_io_throttle device entry "
+                             "was not in expected format"));
             goto cleanup;
         }
 
-        if ((current_dev = virJSONValueObjectGetString(temp_dev, "device")) == NULL) {
+        if (!(current_dev = virJSONValueObjectGetString(temp_dev, "device"))) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("block_io_throttle device entry was not in expected format"));
+                           _("block_io_throttle device entry "
+                             "was not in expected format"));
             goto cleanup;
         }
 
@@ -3689,49 +3701,22 @@ qemuMonitorJSONBlockIoThrottleInfo(virJSONValuePtr result,
         if (STREQ(current_dev, device))
             continue;
 
-        found = 1;
+        found = true;
         if ((inserted = virJSONValueObjectGet(temp_dev, "inserted")) == NULL ||
             inserted->type != VIR_JSON_TYPE_OBJECT) {
             virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("block_io_throttle inserted entry was not in expected format"));
+                           _("block_io_throttle inserted entry "
+                             "was not in expected format"));
             goto cleanup;
         }
 
-        if (virJSONValueObjectGetNumberUlong(inserted, "bps", &reply->total_bytes_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read total_bytes_sec"));
-            goto cleanup;
-        }
+        GET_THROTTLE_STATS("bps", total_bytes_sec);
+        GET_THROTTLE_STATS("bps_rd", read_bytes_sec);
+        GET_THROTTLE_STATS("bps_wr", write_bytes_sec);
+        GET_THROTTLE_STATS("iops", total_iops_sec);
+        GET_THROTTLE_STATS("iops_rd", read_iops_sec);
+        GET_THROTTLE_STATS("iops_wr", write_iops_sec);
 
-        if (virJSONValueObjectGetNumberUlong(inserted, "bps_rd", &reply->read_bytes_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read read_bytes_sec"));
-            goto cleanup;
-        }
-
-        if (virJSONValueObjectGetNumberUlong(inserted, "bps_wr", &reply->write_bytes_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read write_bytes_sec"));
-            goto cleanup;
-        }
-
-        if (virJSONValueObjectGetNumberUlong(inserted, "iops", &reply->total_iops_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read total_iops_sec"));
-            goto cleanup;
-        }
-
-        if (virJSONValueObjectGetNumberUlong(inserted, "iops_rd", &reply->read_iops_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read read_iops_sec"));
-            goto cleanup;
-        }
-
-        if (virJSONValueObjectGetNumberUlong(inserted, "iops_wr", &reply->write_iops_sec) < 0) {
-            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
-                           _("cannot read write_iops_sec"));
-            goto cleanup;
-        }
         break;
     }
 
@@ -3746,6 +3731,7 @@ qemuMonitorJSONBlockIoThrottleInfo(virJSONValuePtr result,
 cleanup:
     return ret;
 }
+#undef GET_THROTTLE_STATS
 
 int qemuMonitorJSONSetBlockIoThrottle(qemuMonitorPtr mon,
                                       const char *device,