[PATCH] qemu_agent: Report error class at least

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

Currently, qemu GA is not providing 'desc' field for errors like
we are used to from qemu monitor. Therefore, we fall back to this
general 'unknown error' string. However, GA is reporting 'class' which
is not perfect, but much more helpful than generic error string.
Thus we should fall back to class firstly and if even no class
is presented, then we can fall back to that generic string.

Before this patch:
virsh # dompmsuspend --target mem f16
error: Domain f16 could not be suspended
error: internal error unable to execute QEMU command
'guest-suspend-ram': unknown QEMU command error

After this patch:
virsh # dompmsuspend --target mem f16
error: Domain f16 could not be suspended
error: internal error unable to execute QEMU command
'guest-suspend-ram': CommandNotFound
---
 src/qemu/qemu_agent.c |   14 ++++++--------
 1 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/qemu/qemu_agent.c b/src/qemu/qemu_agent.c
index b759b7f..decfd0e 100644
--- a/src/qemu/qemu_agent.c
+++ b/src/qemu/qemu_agent.c
@@ -1035,19 +1035,17 @@ static const char *
 qemuAgentStringifyError(virJSONValuePtr error)
 {
     const char *klass = virJSONValueObjectGetString(error, "class");
-    const char *detail = NULL;
+    const char *detail = virJSONValueObjectGetString(error, "desc");
 
     /* The QMP 'desc' field is usually sufficient for our generic
-     * error reporting needs.
+     * error reporting needs. However, older agents did not provide
+     * any 'desc'. Reporting 'class' is not perfect but better
+     * than bare 'unknown error'.
      */
-    if (klass)
-        detail = virJSONValueObjectGetString(error, "desc");
-
-
-    if (!detail)
+    if (!detail && !klass)
         detail = "unknown QEMU command error";
 
-    return detail;
+    return detail ? detail : klass;
 }
 
 static const char *
-- 
1.7.8.5

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