From f30fd1354a01c45a538541db091934d6e687ebcb Mon Sep 17 00:00:00 2001
From: NingBo <ning.bo9@zte.com.cn>
Date: Thu, 29 Nov 2018 16:20:03 +0800
Subject: [PATCH] qmp: Output error detail when execute QMP command failed

Only get 'QMP command failed' error message now when execute QMP
command by 'executeCommandWithResponse' failed. This patch will
output more error detail.

Signed-off-by: NingBo <ning.bo9@zte.com.cn>
---
 qemu/qmp.go | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/qemu/qmp.go b/qemu/qmp.go
index 43daed369..a5da684ef 100644
--- a/qemu/qmp.go
+++ b/qemu/qmp.go
@@ -313,7 +313,7 @@ func (q *QMP) finaliseCommandWithResponse(cmdEl *list.Element, cmdQueue *list.Li
 		if succeeded {
 			cmd.res <- qmpResult{response: response}
 		} else {
-			cmd.res <- qmpResult{err: fmt.Errorf("QMP command failed")}
+			cmd.res <- qmpResult{err: fmt.Errorf("QMP command failed: %v", response)}
 		}
 	}
 	if cmdQueue.Len() > 0 {
@@ -325,6 +325,23 @@ func (q *QMP) finaliseCommand(cmdEl *list.Element, cmdQueue *list.List, succeede
 	q.finaliseCommandWithResponse(cmdEl, cmdQueue, succeeded, nil)
 }
 
+func (q *QMP) errorDesc(errorData interface{}) (string, error) {
+	// convert error to json
+	data, err := json.Marshal(errorData)
+	if err != nil {
+		return "", fmt.Errorf("Unable to extract error information: %v", err)
+	}
+
+	// see: https://github.com/qemu/qemu/blob/stable-2.12/qapi/qmp-dispatch.c#L125
+	var qmpErr map[string]string
+	// convert json to qmpError
+	if err = json.Unmarshal(data, &qmpErr); err != nil {
+		return "", fmt.Errorf("Unable to convert json to qmpError: %v", err)
+	}
+
+	return qmpErr["desc"], nil
+}
+
 func (q *QMP) processQMPInput(line []byte, cmdQueue *list.List) {
 	var vmData map[string]interface{}
 	err := json.Unmarshal(line, &vmData)
@@ -339,7 +356,7 @@ func (q *QMP) processQMPInput(line []byte, cmdQueue *list.List) {
 	}
 
 	response, succeeded := vmData["return"]
-	_, failed := vmData["error"]
+	errData, failed := vmData["error"]
 
 	if !succeeded && !failed {
 		return
@@ -353,6 +370,14 @@ func (q *QMP) processQMPInput(line []byte, cmdQueue *list.List) {
 	}
 	cmd := cmdEl.Value.(*qmpCommand)
 	if failed || cmd.filter == nil {
+		if errData != nil {
+			desc, err := q.errorDesc(errData)
+			if err != nil {
+				q.cfg.Logger.Infof("Get error description failed: %v", err)
+			} else {
+				response = desc
+			}
+		}
 		q.finaliseCommandWithResponse(cmdEl, cmdQueue, succeeded, response)
 	} else {
 		cmd.resultReceived = true