[libvirt] [PATCH] qemu: Refactor parsing of block device IO tuning parameters.

[Peter Krempa]

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.
---
Old error message looks like:
# virsh blkdeviotune asdf hda
error: Unable to get block I/O throttle parameters
error: internal error cannot read total_bytes_sec

and the new:
# virsh blkdeviotune asdf hda
error: Unable to get block I/O throttle parameters
error: internal error block_io_throttle field 'total_bytes_sec' missing in qemu's output

 src/qemu/qemu_monitor_json.c |   66 ++++++++++++++++-------------------------
 1 files changed, 26 insertions(+), 40 deletions(-)

diff --git a/src/qemu/qemu_monitor_json.c b/src/qemu/qemu_monitor_json.c
index dd6536f..3ede88d 100644
--- a/src/qemu/qemu_monitor_json.c
+++ b/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,
-- 
1.7.8.6